Supramolecular Cross-Link-Regulated Emission and Related

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Supramolecular Crosslink-Regulated Emission and Related Applications in Polymer Carbon Dots Tanglue Feng, Shoujun Zhu, Qingsen Zeng, Siyu Lu, Songyuan Tao, Junjun Liu, and Bai Yang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b14857 • Publication Date (Web): 22 Nov 2017 Downloaded from http://pubs.acs.org on November 23, 2017

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ACS Applied Materials & Interfaces

Supramolecular Crosslink-Regulated Emission and Related Applications in Polymer Carbon Dots Tanglue Feng,† Shoujun Zhu,‡ Qingsen Zeng,† Siyu Lu,§ Songyuan Tao,† Junjun ,

Liu,† and Bai Yang* † †

State Key Laboratory of Supramolecular Structure and Materials, College of

Chemistry, Jilin University, Changchun, 130012, P. R. China. ‡

Laboratory of Molecular Imaging and Nanomedicine, National Institute of

Biomedical Imaging and Bioengineering , National Institutes of Health, 35 Convent Dr, Bethesda, MD 20892 USA §

College of Chemistry and Molecular Engineering, Zhengzhou University, 100 Kexue

Road, Zhengzhou 450001 China Corresponding author: [email protected]

1

ACS Paragon Plus Environment


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ABSTRACT Involvement of clear photoluminescence (PL) mechanism in specific chemical structure is at forefront of carbon dots (CDs). Supramolecular interaction existing in plenty of materials, offers an inherent way to administrate the optical and photophysical properties, especially in terms of newly developed polymer carbon dots (PCDs). However, supramolecular interaction-derived PL regulation is always ignored in the shadow of many kinds of PL factors, and we still have a limited understanding on the distinct chemical structure and mechanism of supramolecular effect in PCDs. Herein, several distinct photoluminescent phenomena of PCDs under aqueous and solid state are reviewed in terms of supramolecular crosslinking, with highly emphasizing the importance of supramolecular crosslink-enhanced emission (SCEE) effects, and the regulated function of supramolecular interaction’s intensity and types between PCDs for special PL behaviors of PCDs. In addition, we categorize the photoluminescent phenomena in PCDs as following aspects: supramolecular crosslink-enhanced

dilute-solution-state

emission,

concentration-controlled

multi-color emission, supramolecular regulation for quenching-resistant solid-state fluorescence, as well as supramolecular crosslink-assisted room-temperaturephosphorescence (RTP) under solid states. Furthermore, the applications of PCDs in light-emitting diodes (LED), solar cells, and anti-counterfeiting and data encryption, etc., are presented, based on the distinct supramolecular crosslink-regulated photoluminescent phenomena, especially the solid-state emission. Finally, a brief outlook is given, with highlighting the currently existed problems and development direction of supramolecular crosslink-regulated emission in PCDs.

KEYWORDS: polymer carbon dots (PCDs), crosslink-enhanced emission (CEE), supramolecular interaction, Supramolecular CEE, solid-state emission, room temperature phosphorescence (RTP).

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1 INTRODUCTION As our understanding of the emerging polymer carbon dots (PCDs), one of the fluorescence carbon nanomaterials, has advanced, increasing numbers of innovative properties are being developed, including bright luminescence, high optical and chemical

stability,

good

water-solubility,

photobleaching

resistance,

good

biocompatibility and low toxicity, as well as low cost, etc.1-4 It is particularly true that these excellent properties made PCDs promising in diverse research field, for instance, chemical and biological sensing,5-8 bioimaging,3,

9-11

theranostic,12-16 light-emitting

diodes,17-20 photocatalysts21-25 and solar cells,26-27 etc. Generally, there are four types of chemical structures in PCDs, including non-conjugated chains,28-30 functional groups,31-33 conjugated ring-like structure34-37 and supramolecular interaction-derived crosslink structure36, 38-39. Therefore, researchers can regulate the photoluminescence (PL) properties of PCDs by multiple strategies, such as element doping,34,

40-41

conjugation strategy,35, 42-44 surface modification,45-46 composite engineering47-49 and supramolecular crosslink-regulated emission,39, 50-52 etc. However, as a special method of constructing aggregation state, supramolecular strategy, which has emerged in previous works but been not clearly proposed and well summarized, can offer a special way to tune the optical and photophysical properties of PCDs in terms of supramolecular interaction. In terms of crosslink, similar to restriction of intramolecular motion mechanism of aggregation induced emission (AIE) phenomenon,53-55 the supramolecular crosslinking can inhibit the non-radiation decay channel of excited state even form energy transfer, enhancing photoluminescence of PCDs, even changing PL colors. On the one hand, as our previous articles56-59, the crosslink-enhanced emission (CEE) effect was proposed and proved to elucidate the PL mechanism of PCDs. Typically, the PL properties of some PCDs were attributed to some potential chemical groups (named as sub-fluorophores), such as heteroatom-containing double bonds (C=O, C=N, N=O) and single bonds (amino-based groups, C-O). These sub-fluorophores show generally weak fluorescence while can show increased PL with suitable 3



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immobilization, such as covalent/supramolecular crosslinking or even physical aggregation.56, 59 This experimental success is also reflected in the growing number of reported cases39, 52, 60-62. That is, supramolecular crosslinking can be used to enhance the photoluminscence by inhibiting the motion of fluorescence center, and we named the supramolecular crosslink-enhanced emission effect as SCEE effect. On the other hand, the intensity and types of supramolecular crosslinking between PCDs are important, which provides us a rational design thought for regulating the PL properties of PCDs. The regulation for intensity and types of supramolecular crosslinking possible can form energy (or charge) transfer, or generate new narrow bandgap, thus enhancing the fluorescence and even changing PL colors. Given its increasing importance as the key chemical structure for modulating the PL of PCDs, we focus this review on some unique photoluminescent phenomena of PCDs in terms of supramolecular crosslinking, as well as related applications. In section 2 and 3, we elucidate distinct fluorescence properties of PCDs under dilute solution state, concentrated solution state, individual solid state and solid-state composites, respectively. We highly emphasize the importance of regulating the intensity and types of supramolecular interaction between PCDs, for example, different concentration-controlled multi-color emission, and the realization of quenching-resistant photoluminescent PCDs under solid state by weakening the π-π interaction crosslink. In section 4, distinct room temperature phosphorescence (RTP) properties of PCDs under solid state is reviewed in terms of hydrogen bond. In section 5, based on these distinct supramolecular crosslink-regulated photoluminescent phenomena, especially the solid-state emission, we review some applications of PCDs in light emitting diodes (LED), solar cells, fingerprint detection, anti-counterfeiting and data encryption, etc. Finally, a brief outlook is given, with highlighting the currently existed problem, corresponding solutions and development direction in the future. We hope that this review provides accurate definition on distinct supramolecular-regulated emission of PCDs and their applications, eventually promoting the further development of PCDs. 4


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2 Supramolecular interaction-regulated emission in solution-state PCDs The concentration of PCDs in solvent determines the interparticle distance, which influences the surface electron distribution of PCDs by supramolecular crosslinking. Thus, the supramolecular crosslinking-regulated PCDs’ emission in solution are elucidated from dilute solution and concentrated solution, respectively.

2.1 SCEE effect of PCDs in dilute solution SCEE co-existing generally in covalent bond-based PCDs system, together with covalent CEE, plays important role in the fabrication and photoluminescence of PCDs. Highly crosslinked fluorescent polymers or assembled hybrids, a type of PCDs, were reported by supramolecule crosslink-assisted synthesis at facile conditions, with the PL of PCDs enhanced. Yang’s group reported the synthesis of aliphatic biodegradable photoluminescent polymers (BPLPs) and crosslinked variants (Figure 1A) from small molecules.63 In the crosslinked variants, the supramolecular interaction (multiple hydrogen bonds) CEE together with covalent bond CEE contributed to the enhanced PL. Sun’s group reported the synthesis of photoluminescent copolymer (PEI-PLA) (Figure

1B)

for

biomedical

application

by

self-assembling

hydrophilic

polyethyleneimine PEI with hydrophobic polyactide (PLA), in which supramolecular interaction-derived compact network structure was main origin of enhanced PL due to the fixation of sub-fluorophore.64 Other types of photoluminescent PCDs, such as tri-block copolymer (PEG-PAsp(MEA)-PEI),65 biohybrid (aggregated DNA dots),66 were also synthesized through self-assembly route.

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Figure 1. Supramolecular crosslink-assisted synthesis and emission of PCDs. (A) Synthesis of BPLPs. Reproduced with permission of Proceedings of the National Academy of Science of the United States of America from Ref 63. (B) The construction of multifunctional PCDs from hydrophilic PEI and hydrophobic PLA amphiphilic copolymer. Reprinted with permission of Nature Publishing Group from Ref 64. (C) A schematic illustration of the relationship between different products in the PCDs prepared from citric acid (CA) and ethylenediamine (EDA). Reproduced with permission of Royal Society of Chemistry from Ref 72.

Furthermore, the SCEE effect also exists in partly carbonized PCDs. In general, the formation of PCDs undergo in sequence dehydration/polycondersation, assembly/crosslinking and carbonization from small molecules or polymer precursors,36, 39, 67-70 and supramolecular interaction plays a crucial role in assembly and crosslinking process. Yu’s group prepared highly blue fluorescent N,S-dopped PCDs through one-pot hydrothermal condensation from citric acid (CA) and cysteamine (Cys).36 The author found the dehydration between CA and Cys produced a molecular fluorophore with the photoluminescent quantum yield (PLQY) of 0.88. Furthermore, they proposed that the molecular fluorophore can self-assemble into amorphous PCDs core with PLQY of 0.66 through hydrophobic interaction and π−π stacking interaction. In fact, similar works67, 71-73 had been reported by our (Figure 1C) and other groups before this work though the mechanism of supramolecular interaction-induced self-assembly of molecular fluorophore into PCDs were not 6


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explicitly proposed in these literatures. Recently, Fang’s group39 investigated in detail the structure of molecular fluorophore assembly and PL mechanism of highly fluorescent citric-acid derived PCDs. The author found that molecular fluorophores (Figure 2A(b,c)), a five-membered ring fused 2-pyridone organics, were the origin of strong fluorescence, and the individual molecular units could link together through hydrogen bond, generating dimer, trimer, etc., and the presence of star-shaped polymer DETA@5CA (Figure 2A(d,e)), also proved the contribution of hydrogen bonds to the formation of PCDs assembly hybrid. Thus, the molecular fluorophores, as-fabricated dimer, trimer together with supramolecule (star-shaped polymer DETA@5CA) were considered as the main origin of bright PL and spherical morphology of the as-synthesized PCDs.

Figure 2. Supramolecular crosslink-assisted synthesis and emission of PCDs. (A) a. Chromatograms for the elution of PCDs monitored by PDA at 254 nm. High resolution mass spectra (b and d) and 1HNMR spectra (c and e) of fraction I (b and c) and fraction II (d and e). [39] - published by The Royal Society of Chemistry. (B) The formation of supra-CDs and water-induced PL enhancement behavior. Reproduced with permission of Wiley-VCH from Ref 74.

In the aforementioned supramolecular crosslink-based PL system, the Supramolecular CEE has a minor contribution on the PL of PCDs in contrast with covalent bond CEE. However, supramolecular interaction-based crosslinking structure could also play a major role in enhancing PL for some specific PCDs. Qu’s group 7



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prepared

water-induced

photoluminescent

supra-PCDs

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from

alkyl

chains

functionalized-PCDs by self-assembly as shown in Figure 2B.74 Typically, the alkyl chains functionalized PCDs can self-assemble into supra-PCDs aggregation state in toluene, which show weak fluorescence, and it is surprised that the supra-PCDs can show water-induced PL enhancement owing to the decomposition of supra-PCDs in water. Obviously, the supramolecular hydrophilic/hydrophobic interaction plays a crucial role in the formation of supra-PCDs and the generation of water-induced PL enhancement behaviors of supra-PCDs. Mandal’s group reported the synthesis of PCDs with orange-red emission employing sucrose as the carbon sources.52 The hydroxymethylfurfural (HMF) derivative (Figure 3A) in the PCDs was confirmed by multiple spectroscopic techniques. Considering the HMF derivative has no charge transfer donor–acceptor moiety and no extended conjugation, which can be proved by the medium polarity-independent emission maximum and single exponential PL lifetime, the author demonstrated that the HMF derivative can form crosslinked structures (Figure 3B) through non-covalent interactions such as dipole–dipole, π-π stacking and van der Waals interactions, generating red-shifted orange-red emission. What's more, supramolecular crosslink were also found between PCDs and solvents, which can also change PL properties of PCDs. Yu’s group reported efficient red-emission PCDs from p-phenylenediamine via solvothermal method, and found that as-prepared PCDs showed solvent-dependent multi-color emission from green to red, with fluorescence peak position red-shifting with the increasing of solvent polarity.75 Song’s group investigated in detail the solvent polarity-dependent photoluminescent mechanism, attributing the unique spectral shift to hydrogen bond (HB) effect as shown in Figure 3C, which was verified by fluorescence lifetime and equation simulation.51

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Figure 3. Supramolecular crosslinking structure play major role in PL of PCDs. (A) Formation mechanism of the HMF derivative in PCDs. (B) HMF derivatives’ supramolecular crosslinking structure inside PCDs. [52] - published by the PCCP Owner Societies. (C) a. Schematic illustration about the energy states and electron transition process of PCDs. b. Illustration about the hydrogen bond (HB) effect-dominated PCDs’ emission mechanism between molecule states and solvents. c. Digital photograph of different PCDs-polymer composites. Reproduced with permission of Royal Society of Chemistry from Ref 51.

2.2 Concentration-controlled emission of PCDs For PCDs, there are several strategies to regulate the PL colors, such as separation by column chromatography to extract fractions with specific emission,76-77 introduction of bigger conjugated sp2 system inside PCDs by employing aromatic-containing

precursors,18,

78-80

solvent

engineering,51,

75,

81-82

post-functionalization utilizing surface modifying agent,45-46 and exploiting efficient synthesis methods,83-84 etc. However, besides aforementioned methods, concentration control strategy provides us another facile route to regulate the emission colors of PCDs. It mainly involves the supramolecular crosslink-induced emission mechanism regarding the concentration dependent PL in PCDs. Typically, the concentration of PCDs determines the interparticle distance, and influences the surface electron distribution of PCDs by supramolecular crosslinking (a type of aggregation state), thus allowing the concentration of PCDs to tune their emission states.85 9



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Figure 4. Concentration-dependent emission in PCDs. (A) Concentration-dependent PL behaviors in PCDs. (a-0.12 mg/L, b-0.12 mg/L, c-0.12 mg/L, d-0.12 mg/L) Reproduced with permission of American Chemical Society from Ref 86. (B) Optical photographs of R-, O-, Y-, G- and B-PCDs under ambient (top) and white light irradiation (bottom). (C) TEM and HRTEM images of the Blue-PCDs (a) and Red-PCDs (c) and size histograms of the Blue-PCDs (b) and Red-PCDs (d). [87] - published by The Royal Society of Chemistry. (D) Concentration-mediated luminescence colors ranging from blue to red. Reproduced with permission of Royal Society of Chemistry from Ref 88.

Wang’s group prepared hydrophobic PCDs through hydrothermal treatment of ionic liquid of 1-ethyl-3-methylimidazolium bromide, and the as-obtained PCDs exhibited concentration-dependent PL behaviors as shown in Figure 4A, which were used for multi-color imaging in vitro and in vivo. The red-shifted fluorescence could be ascribed to the energy or charge transfer induced by supramolecular crosslinking between

fluorphores.86

Analogously,

Yu’s

group

also

reported

concentration-dependent full-color fluorescence (Figure 4B) of PCDs prepared from an N-methylpiperazine precursor in MgAPO-44 zeolite by calcination and NaOH treatment. The author claimed that such tunable PL might mainly result from the energy transfer between multiple emitters in the nanoparticles, especially in the highly concentrated PCDs.87 The energy transfer resulted from the supramolecular crosslink-derived aggregation state between adjacent nanoparticles as proved by high-resolution TEM (Figure 4C), and the crosslinking degree determined the energy 10


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transfer degree then PL color. Bai’s group also reported multi-color (blue to red) photoluminescent PCDs (Figure 4D) with stable luminescence character by changing the concentration of PCDs in toluene.88 It should be noted that for the concentration-mediated

multi-color

emission,

the

high-concentration

(i.e.

long-wavelength emission) PCDs generally show lower PLQY compared to the low-concentration (i.e. short-wavelength emission) PCDs as reported by our group

89

because most of PCDs’ PL intensity decreases with the increase of excitation wavelength, and the multi-color emission of PCDs are mainly caused by energy transfer between PCDs particles each other.

3 Supramolecular crosslink-regulated solid-state emission in PCDs Distinct from the solution-state PCDs, PCDs in solid state generally show nondispersive compact (aggregation state) structure, which easily result in luminescence self-quenching. However, the supramolecular crosslinking provide a potential way to conquer the solid-state quenching of PCDs.

3.1 Self-quenching-resistant solid-state fluorescence in PCDs Many fluorescent small molecular dyes with typical conjugated π-domains fluorophores generally suffer from fluorescence quenching under solid state owing to strong π-π interaction (energy-transfer process).90-91 Likewise, if there exist strong π-π interaction or other strong supramolecular interaction in PCDs, the solid-state PCDs generally only show weak even no fluorescence. Our group reported highly fluorescent PCDs from citric acid and ethylenediamine, with a fluorescent small molecule (IPCA)72-73 found, a conjugated ring-like molecule, which is the main origin of strong aqueous solution fluorescence. However, the as-obtained PCDs show no fluorescence under solid state, which possibly was resulted from the strong π-π interaction-caused luminescence quenching between molecule fluorophores. What’s more, most of reports about PCDs only involve aqueous solution fluorescence in general, and the solid-state fluorescence properties were rarely illuminated due to the π-π interaction-caused luminescence quenching. In fact, we claim that the solid-state 11



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luminescence can be greatly enhanced by regulating the supramolecular crosslinking of PCDs to appropriate point, especially reducing even avoiding the fabrication of strong suparmolecular interaction between fluorescence centers.

3.1.1 Supramolecular strategy for solid state emission of small molecule precursor-derived PCDs Small molecule precursor-derived PCDs generally possess high carbonization degree, which will result in the formation of π-domains even ring-like molecules connected on the PCDs' surface due to sufficient dehydration and carbonization. The formed strong π-π interaction under solid state will cause fluorescence quenching. Thus, supramolecular crosslinking regulation strategy provides us a method to enhance the solid-state emission by regulating the types and/or intensity of supramolecular interaction. Typically, inhibiting and avoiding the formation of strong supramolecular interaction in PCDs probably can conquer the fluorescence quenching by some particular strategies, such as carbonization degree control, surface charge engineering, etc. Zhang’s group reported the synthesis of yellowish-green fluorescent PCDs under solid states from calcium citrate and urea by microwave-assisted hydrothermal method as shown in Figure 5A.92 We speculate that the unique solid-state fluorescence can be attributed to the increased electrostatic repulsion between adjacent particles as a result of the presence of calcium ion on the surface of PCDs. Zhou’s group prepared solid-state fluorescent PCDs (SFPCDs) and solid-state non-fluorescent PCDs (SNPCDs) (Figure 5B (a)) from identical precursors (citric acid and urea) through precise control of the microwave reaction conditions.93 The entirely different solid-state emission properties could be attributed to different carbonization degree as shown in Figure 5B (b), which determine the amounts of chemical groups and molecule fluorophores on the surface of PCDs, reflecting the different supramolecular crosslinking degree between adjacent nanoparticles. Kim’s group synthesized boron-and-nitrogen co-dopped PCDs (BN-PCDs) from CA and EDA and boric acid via microwave-hydrothermal treatment. The as-prepared BN-PCDs exhibited exceptionally bright solid states fluorescence (Figure 5C) with 12


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the high PLQY of 67.6%, a champion solid-state PLQY value to date. The author claimed that the bright solid-state emission could be attributed to abundant graphitic structures in the core and well-distributed surface states as a result of boron-and-nitrogen co-doping as shown in Figure 5D.41 In fact, well-distributed surface states possibly play leading role in solid-state fluorescence owing to proper supramolecular crosslinking degree. More recently, our group achieved the red emission of PCDs under solid state (Figure 5E) from maleic acid and EDA via microwave-assisted method, and the aqueous-solution PCDs showed blue fluorescence, with PCDs/polymer composites showing multi-color emission when changing the concentration of PCDs in matrix as shown in Figure 5F,G.89 We think that it can be ascribed to the precise control of facile microwave conditions (form a moderate carbonization degree), which generated red-shifted solid state emission due to supramolecular crosslink-derived energy transfer, and different supramolecular crosslinking degree in polymer matrix can generate different PL color.

Figure 5. Self-quenching resistant solid-state emission of PCDs prepared from small molecules. (A) Preparation of N-doped PCDs, and photoluminescent photograph of N-doped PCDs under daylight and under a 365 nm UV beam. Reproduced with permission of Royal Society of Chemistry from Ref 92. (B) a. Photoluminescent photograph of PCDs powder under daylight and 13



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UV-lamp; b. FTIR spectra of SFPCDs (red line) and SNPCDs (green line), and High-resolution C 1s, N 1s, O 1s spectra of SFPCDs and SNPCDs. Reproduced with permission of Royal Society of Chemistry from Ref 93. (C) The optical properties contrast between nitrogen-doped PCDs and boron-and-nitrogen co-doped PCDs. (D) Schematic structures of the corresponding PCDs. Reproduced with permission of American Chemical Society from Ref 41. (E) Dilute aqueous-solution and solid-state photoluminescent photographs of PCDs under daylight (a) and UV light (b). (F) Photographs of starch (No.1) and photographs of PCDs/starch composites of b-PCDs (No.2), g-PCDs (No.3) and y-PCDs (No.4) under daylight (a) and UV light (b). (G) PCDs/PVA film with full-color emission under UV light. Reproduced with permission of Wiley-VCH from Ref 89.

Currently, advances in our knowledge of supramolecular-regulation emission of PCDs, and innovation in the synthesis of PCDs with solid-state emission are improving. Nevertheless, the most reported PCDs from small molecules show weak even no fluorescence, and challenges remain in this emerging field related to the bright emission at long wavelength. We believe that the multiple supramolecular crosslinking regulation strategies (such as hydrogen bonds, van der Waals interactions, host–guest interactions, and coordination interaction, etc.) will offer probably potential ways to render PCDs generate energy transfer, even form new narrow band-gap, then unique optical properties.

3.1.2 Polymer precursor-derived solid state emission There were several reports about polymer precursor-derived solid-state emission. We think that the using of polymer precursors can make as-synthesized PCDs self-dispersion owing to the formation of crosslinked polymer network structure in PCDs, which weaken strong supramolecular interaction between PCDs. What’s more, the using of polymer precursors can reduce the fabrication of π-domains and ring-like molecules due to the insufficient carbonization in contrast to small molecule precursors, which avoid the strong π-π interaction-caused fluorescence quenching. Chen’s

group

reported

luminescent

poly(styrene-co-glycidylmethacrylate)

PCDs

films

(PS-co-PGMA)

synthesized photonic

from

crystals.94

Subsequently, they reported another fluorescent PCDs under solid state via pyrolysis of poly(acrylic acid) (PAA) in the presence of glycerol.95 Other photoluminescent solid-state PCDs with the using of PVA precursor38, 96 were also reported. Thereinto, 14


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Liu’s group38 ascribed the red-shifted solid-state fluorescence (Figure 6A) in contrast to aqueous-state fluorescence to proper interparticle spacing control (Figure 6B). The polymer precursors-derived PCDs may offer a proper interparticle distance, which not only protect the fluorescence from quenching but also make interparticle energy transfer then red-shifted emission under solid state. What's more, the author also mentioned that overclose interparticle distance (the fabrication of excessive supramolecular crosslinking) will result in fluorescence quenching as shown in Figure 6B.

Figure 6. Quenching resistant solid-state emission of PCDs prepared from polymers (A-B) or silane coupling agent precursors (C-D). (A) Photographs of PCDs from PVA with diethylenetriamine (1), tetraethylenepentamine (2), ethylenediamine (3) or individual PVA (4) under daylight and UV lamp. (B) Schematic diagram of the relationship between fluorescence properties and interparticles spacing distance. Reproduced with permission of Wiley-VCH from Ref 38. (C) Photographs of B-, G-, and T-Si-PCDs/SiO2 nanocomposite powders under irradiation of daylight (top) and UV light (bottom). Reproduced with permission of American Chemical Society from Ref 40. (D) Schematic diagram for the preparation of photoluminescent PCDs and the fabrication of dual-fluorescence PCDs/starch composites. Reproduced with permission of Wiley-VCH from Ref 102.

3.1.3

Silane coupling agent precursor-derived solid-state

emission The using of silane coupling agent precursor is another strategy to conquer the 15



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self-quenching of solid-state PCDs. We take (3-aminopropyl)-trimethoxysilane (APTMS) for example. The reactive amino group can react with other organic acids, participating in the nucleation and growth of PCDs by continuous dehydration, polymerization, carbonization. The long-chain structures contribute to the formation of highly crosslinked polymer network structure in PCDs, and the alkoxy can hydrolyze or alcoholysis with alcoholic hydroxyl group, forming silica network structure on the surface of PCDs. The highly crosslinked polymer and silica net-structure could weaken and reduce strong supramolecular interaction between PCDs under solid state, avoiding the strong π-π interaction-caused fluorescence quenching. Zhang’s group reported the highly luminescent PCDs under solid state firstly by using CA as carbon source, ethanediamine-containing organosilane (AEAPMS) as a coordinating solvent.97 The fluorescent PCDs films or monoliths on the selected substrate or vessel can be obtained via simply heating at low temperature. What’s more, the as-prepared Si-PCDs were also functionalized with other silane coupling agents to fabricate luminescent gel glasses.98 However, the as-synthesized Si-PCDs was water-insoluble. Chang’s group reported the preparation of strongly fluorescent Si-PCDs under solid state from APTMS via one-pot hydrothermal method. The as-prepared Si-PCDs exhibited excellent photostability and high water-solubility.99 Similar works100-101 with more detailed optical properties characterization, were also reported

by

Liu’s

group

from

CA

and

N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEATEMS or KH-792). The PCDs with long-wavelength fluorescence under solid state have been the subject interests for researchers, contributing to bioimaging and multi-color light-based applications. Chang’s group prepared multi-color luminescent solid-state Si-doped PCDs (Figure 6C) via hydrothermal method followed by calcination of powder or film. They attributed the heat-induced PL red-shifting to the combination of several factors, including the formation of SiO2 in PCDs owing to the hydrolysis of the excess APTMS, change in sizes and composition of Si-PCDs during heating.40 These heat-induced-structure changes could make supramolecular crosslinking 16


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changed, influencing the energy transfer and PL colors. However, it should be noted that the PLQY of the as-prepared blue-, green- and tan-emitting Si-PCDs powders were only 6.7, 0.6, and 0.1%, respectively. Recently, Lei’s group reported solid-state red-fluorescent Si-PCDs with upper PLQY of 9.60% and great water-solubility from CA and 3-(2-Aminoethylamino) propyl-dimethoxymethylsilane (AEAPMS or KH-602), with acetone acting as solvent as shown in Figure 6D.102 It should be noted that the as-prepared PCDs exhibited blue fluorescence under aqueous solution with PLQY of 50.7%, namely showing dual-fluorescence morphologies emission between solid state and liquid state. The large red-shift of PL wavelength was ascribed to the supramolecular crosslink-induced Förster resonance energy transfer (FRET) as proved by solvent-dependent PL in aqueous solution, humidity and concentration-determined PL colors for solid PCDs/starch nanocomposites. What’s more, introducing silane coupling agents into the aqueous-solution red fluorescent PCDs system, can also generate red fluorescent PCDs under solid state. For example, Xie’s group synthesized

red

fluorescent

PCDs

under

solid

state

from

3-isocyanatopropyltriethoxysilane (IPTS) and p-phenylenediamine via solvothermal method.103

17



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Figure 7. PCDs-based composites with quenching resistant solid-state emission. (A) Schematic illustration of the formation mechanism of starch/PCDs phosphors. (B) a. Optical photographs of starch/green-PCDs (left) and starch/blue-PCDs (right) phosphors under room light (top) and UV lamp (down). b. Luminescent blocks fabricated from starch/blue-PCD (left) and starch/green-PCD (right) phosphors in epoxy silicone resin under room light (above) and UV lamp (below). Reproduced with permission of Royal Society of Chemistry from Ref 20. (C) Multi-color composites films based on PCDs with polymers (160 and 240 represent the prapration temprature. Reproduced with permission of Nature from Ref 114. (D) The preparation of luminescent PCDs/PDMS films by one-pot thermal treatment route. Distinct multi-color PCDs were prepared by using different precursors. [115] - published by The Royal Society of Chemistry. (E) Chemical structure of TMA-POSS (a), photoluminescent photographs (b) and TEM images (c) of PCD@TMA-POSS powders under daylight (top) and UV light (bottom). Reproduced with permission of Royal Society of Chemistry from Ref 116. (F) The fabrication mechanism of PCDs@BaSO4 hybrid phosphors. Reproduced with permission of Wiley-VCH from Ref 120.

3.2 PCDs-based solid-state fluorescent composites The supramolecular crosslinking of PCDs under solid state is generally excessive owing to the presence of some strong supramolecular interaction (such as π-π interaction), and effective methods to conquer excessive supramolecular crosslinking for bright solid-state emission are required. In addition to the above-mentioned 18


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self-quenching-resistant strategies, compositing PCDs with polymer or inorganic matrix is another efficient strategy to conquer the excessive supramolecular crosslink-caused luminescence quenching.

3.2.1 Polymer matrix Polymer has been considered to be good anti-aggregation agent for many luminescent

materials,

such

as

nanocrystals,104

nanoclusters,105

etc.

For

PCDs/polymer composites, the polymers can disperse the crosslinked PCDs under solid state, and their functional groups can form hydrogen bond with PCDs’ surface groups. Shen and co-workers developed strong luminescent PCDs/starch composites (Figure 7A,B) with high PLQY of about 50%.20 The author thought that the formative hydrogen bonds between hydroxyl groups of starch particles and carboxyl and amide groups of PCDs surface, suppressed the non-radiative decay processes, thus generating quenching-resistant emission. Analogous luminescent PCDs/polymer composites were also reported by employing other polymers. These polymers include poly

vinyl

alcohol

(PMMA),110-112

(PVA),106-108

epoxy

resin,109

poly(N,N'-dimethylacrylamide)

polymethyl

(PDMAA),68

methacrylate

Silicone,113

etc.

Interestingly, Zeng’s group found that the PCDs dispersed in different polymer matrixes can presented different PL colors as shown in Figure 7C, even when the same PCDs were used.114 What’s more, Raz Jelinek’s group reported the in-situ synthesis of color-tunable (green, yellow and orange) and strongly luminescent PCDs/PDMS composites (Figure 7D) by employing different PCDs precursors through a simple one-pot thermal treatment,115 which provided a new strategy for constructing highly color-tunable fluorescent light emitters.

3.2.2 Inorganic matrix Inorganic matrix can also be used to weaken the excessive supramolecular crosslinking (π-π interaction) of PCDs under solid state. Rogach’s group reported the fabrication of highly luminescent solid-state luminophores with strong deep blue emission and a record high PLQY of 60% by integrating water-soluble PCDs with an octa(tetramethylammonium)-functionalized polyhedral oligomeric silsesquioxane 19



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(TMA-POSS) as shown in Figure 7E.116 Other inorganic matrixes, such as SiO2,117 NaCl118-119

were also employed to form solid-state luminescent composites.

Moreover, supramolecular assembly strategy was also used to fabricate solid-state luminescent hybrids. Qu’s group fabricated PCDs/BaSO4 hybrid (Figure 7F) in an easy and low-cost process by sequentially assembling Ba2+ and SO42− ions onto the surface of PCDs.120 The as-fabricated PCDs/BaSO4 hybrid exhibited excellent photothermal stability with PLQYs of 27%, as well as remarkable resistance to strong acid/alkali and common organic solvents.

4 SCEE effect-assisted room temperature phosphorescence of PCDs The concepts of PCDs, derived from the research field of CDs, are just put forward recently, and there are still many novel properties waiting to be exploited. The room-temperature phosphorescent (RTP) property of PCDs is one of the interesting properties, which was achieved by integrating as-prepared PCDs in matrix materials, such as polymer, inorganic crystalline materials. We emphasize that the supramolecular interaction between PCDs and matrix materials plays an important role in the generation of RTP phenomenon. For polymer matrix, there exists many oxygen/nitrogen containing functional groups (such as C=O, -NH2, -OH, etc.), which can form large amounts of hydrogen bonds with the potential triplet state groups (such as C=N, C=O) of PCDs under solid state. The as-fabricated supramolecular crosslinking could effectively lock the emissive species, and inhibit their intramolecular motions and the nonradiative relaxation channel, generating RTP emission. In 2013, Zhao’s group reported the first example of PCDs-based RTP (Figure 8A) by embedding PCDs into poly(vinyl alcohol) (PVA) matrix, and its phosphorescent lifetime was up to the subsecond (380 ms) as shown in Figure 8B. The generation of phosphorescence was attributed to the triplet state of C=O bonds, but it can’t produce RTP phenomenon when PCDs were dispersed in water, cellulose paper or PEG 20000, etc.121 That is, the PVA matrix plays a crucial role in the generation of RTP. The author thought that large amounts of 20


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hydrogen bonds could be formed between the C=O of PCDs and the hydroxyl group of PVA as shown in Figure 8C. The hydrogen bond-induced crosslinking fixation effects effectively inhibit the nonradiative relaxation channel then promote the generation of RTP. Subsequently, similar phenomena were also reported by many groups by dispersing as-prepared PCDs into poly(vinyl alcohol) (PVA),49,

122

polyurethane (PU)123. Furthermore, there was a report about the self-confined RTP phenomenon (Figure 8D) of PCDs prepared from PVA and ethylenediamine, with no matrix used.124 We think that the using of polymer precursors can make as-synthesized PCDs partly maintain polymeric structure. Thus, crosslinked polymer network structure could be formed by covalent-bond crosslinking by dehydration condersation and supramolecular interaction crosslinking by H-bond between interchains, which can effectively lock the emissive species. Inorganic crystalline structure is an alternative to fabricate PCDs-based RTP hybrids. Most reported works illuminated that the confine effects of inorganic crystalline structure were the main origins of PCDs’ RTP properties by rigidifying triplet excitons (potential phosphorescence center) then suppressing non-radiative relaxation. These inorganic crystalline structures contain layered double hydroxides (LDHs),125 KAl(SO4)2▪xH2O126. However, Zhou’s group reported the supramolecular interaction-assisted RTP emission by one-pot heating treatment for the mixture of urea and as-prepared PCDs. They elucidated that the C=N bond on the surface of PCDs was potential phosphorescence center, and the RTP emission was ascribed to the fabrication of composite matrices (the melting recrystallization urea and biuret fabricated from the heating urea), which played a dual role to suppress the vibrational dissipation of long-lived triplets by combining the rigidity of the melting recrystallization urea and hydrogen bond-induced crosslinking effects between biuret and PCDs as shown in Figure 8E.50

21



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Figure 8. Room temperature phosphorescence (RTP) properties of PCDs. (A) The photoluminescent spectra of PCDs and PCDs/PVA composites: dispersed in water (blue line) and PVA matrix under UV light (cyan line), and after UV light has been turned off (olive line). (B) Time-resolved phosphorescence spectrum. (C) Proposed phosphorescence mechanism of PCDs dispersed in the PVA matrix. Reproduced with permission of Royal Society of Chemistry from Ref 121. (D) Schematic diagram of supramolecular crosslinking model of RTP emission. Reproduced with permission of Royal Society of Chemistry from Ref 124. (E) Photoluminescent photograph of PCDs embedded into melting recrystallization urea and biuret matrices under UV light and after UV light has been turned off, and schematic illustration of possible energy structures of C=N bonds and phosphorescent emission processes. Reproduced with permission of American Chemical Society from Ref 50.

Currently, the investigation of PCDs’ RTP phenomenon is still in preliminary stage, more efforts need to be done to solve some crucial science issues, including origin of PCDs’ RTP phenomenon, and the relationship between the fluorescence and phosphorescence in PCDs. Moreover, it is highly desired to find new strategies to improve RTP performances (color, PLQY, etc.), achieve more self-confinement PCDs RTP systems without matrices, even delay fluorescence by confining PCDs in other rigidity matrixes containing porous or cage-like structure. The construction and regulation of efficient supramolecular crosslinking network based on multiple types of supramolecular interaction, will provides us powerful routes to improve RTP performances.

22


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5 Related applications In the aforementioned sections, we mainly focus on the supramolecular crosslink-regulated photoluminescence properties of PCDs, emphasizing highly the solid-state emissions of PCDs. Thus, this section mainly introduce some solid-state emission-derived

applications,

including

phosphor

light

emitting

diodes,

down-conversion solar cells, RTP-derived anti-counterfeiting and data encryption applications, with few supramolecular-regulated aqueous-state applications involved. We hope this section could encourage researchers to expand the applications of these novel materials. Of course, some biological applications, such as bioimaging, drug delivery and therapy, also belong to the applications ranges of PCDs mentioned in this review, but the biologically related applications will not be elucidated in this review considering there have been number of reviews for the biological applications of PCDs.

5.1 Phosphor Light Emitting Diodes PCDs present considerable potential in light emitting diodes (LEDs) owing to excellent PL properties, especially as phosphor conversion layer. The PCDs-based phosphors LEDs possess definite superiority in contrast to the rare earth iron and quantum dots-based phosphors, including great optical stability, cheap raw materials and low toxicity. Generally, the most of as-prepared PCDs can be dispersed directly in various polymer matrices to form PCDs/polymer composites (section 3.2.1) phosphors, which were coated on ultraviolet or blue emissive GaN chips for LEDs applications as shown in Figure 9 68. In addition, the distinct self-quenching-resistant fluorescent PCDs under solid state (section 3.1.2 and 3.1.3) were also reported to construct phosphors by mixing with polymer, with elevated performances presented. Inorganic matrix-dispersed PCDs (section 3.2.2) were also reported to fabricate PCDs-based composite phosphors by combining with polymer. Moreover, liquid-phase-based LEDs without matrix were also achieved. Bai’s group reported liquid-state PCDs-based multi-color (blue to red) LEDs with stable luminescence characters by changing the concentration of PCDs in toluene as shown in Figure 10A. 23



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The PCDs were stored in a glass box and packaged with a UV-LED chip.88 Furthermore, PCDs can also be combined with other luminescent materials to fabricate composites phosphor for white LEDs, such as quantum dots,88,

116

conjugated polymer dots,127 rare earth,128 etc. For example, Liu’s group constructed dual-emitting core-shell PCDs/silica phosphor (PCDSP) from PCDs, tetraethoxysilane (TEOS) and Sr2Si5N8:Eu2+ via one-pot sol–gel method as shown in Figure 10B, achieving white light emission. Then, PCDSP were mixed with epoxy resin to fabricate white LEDs with a high color rendering index (CRI) of 94.128

Figure 9. (A) Photograph of poly(N,N'-dimethylacrylamide) (PDMAA)/PCDs phosphor white LEDs. (B) Emission spectra of white LEDs. (C) Color coordinate (0.29, 0.31) of LEDs. The bulk polymer/PCDs composites phosphor’s photograph under daylight (D) and under UV lamp at different temperature (E-G). Reproduced with permission of American Chemical Society from Ref 68.

However, the above-mentioned reports are almost white color phosphor LEDs for daily illumination, only few other colors LEDs with inferior color purity were obtained owing to broad spectral widths. To achieve the monochrome phosphor LEDs devices based on PCDs for multi-color displays, Rogach’s group reported a series of monochromatic phosphor LEDs based on monodisperse PCDs prepared from CA and N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane (AEAPMS) via pyrolysis method, in which the colors were determined by the thickness of the down-conversion layers or the concentration of PCDs in the polymer matrix as shown in Figure 10C.19 Rhee’s group chemically modified the surface of PCDs using a series of 24


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para-substituted anilines

to control their PL properties,

endowing

PCDs

long-wavelength photoluminescence (up to 650 nm) and narrow spectral widths. Then, the monochrome LEDs devices (Figure 10D) were achieved by using the functional PCDs/PMMA composite as phosphor.46 What’s more, the single solid-state fluorescent PCDs prepared from small molecules was also used to fabricate full-color and white color LEDs by our group as shown in Figure 10E,89 which was a new strategy of constructing full-color and white color LEDs using only a kind of solid-state fluorescent PCDs. It should be noted that the PCDs possessed short-wavelength aqueous-solution emission (blue) and long-wavelength solid-state emission (red) as shown in Figure 6A.

Figure 10. LEDs applications of PCDs. (A) PCDs LEDs’ PL spectra (a), CIE color coordinates (b) and LEDs’ photographs (c) of blue, green, yellow and red luminescence of UV-LED under 3 V. Reproduced with permission of Royal Society of Chemistry from Ref 88. (B) The formation process of PCDSP through one-pot sol–gel method, the left inset is the photographs of PCDSP under daylight (left) and UV light of 365 nm (right), the right inset is photograph of a PCDSP-based white LEDs. Reproduced with permission of Royal Society of Chemistry from Ref 128. (C) a. Schematic diagram of the monochromatic PCDs-LEDs with PCDs embedded in a 25



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PMMA matrix with a variable layer thickness on top of a UV-LED chip. (b, c). The thickness of the PCDs active layer-dependent PL colors of PCDs-LEDs. Reproduced with permission of Royal Society of Chemistry from Ref 19. (D) Emission spectra of multi-color LEDs. The intensity is normalized for easy comparison, the inset is the photoluminescent photographs of LEDs during operation. Reproduced with permission of Nature from Ref 46. (E) Photograph (I), emission spectra (II) and CIE color coordinate (III) of the LEDs by mixing PCDs/starch composites or PCDs powder with curable resin, with blue (a), green (b), yellow (c), red (d) and white (e) light showed, respectively. Reproduced with permission of Wiley-VCH from Ref 89.

PCDs is increasingly used to fabricate color-conversion layer of LEDs, but it is far from satisfactory in aspects of luminance, color purity, etc. Thus, there is a long way to go to achieve high-performance PCDs phosphor LEDs. Firstly, some extra strategies need to be employed to conquer preferably the fluorescence quenching of PCDs under solid state, such as searching excellent matrixes beneficial to the solubility and dispersity of PCDs. What’ more, it is highly desired to design and prepare the brightly multi-color luminescent PCDs under solid-state for achieving bright multi-color LEDs. Finally, the fabrication procedure of devices need to be optimized, especially the thickness control of phosphor coated on the GaN LED chips, which plays a crucial role in the luminance and color purity of phosphor-based LEDs.

5.2 Down-conversion solar cells Zhang’s group applied the solid-state luminescent PCDs prepared from ascorbic acid and N-(2-aminoethyl)-3-aminopropyltriethoxysilane (KH791) as light down-conversion layers of inverted polymer-fullerene-based bulk heterojunction (BHJ) solar cells (Figure 11A), improving the power conversion efficiency (PCE) by about 12% (Figure 11B).129 They found that the PCDs can boost certainly the light-harvesting of solar cells in near ultraviolet and blue-violet portions of sunlight on the basis of the luminescent down-shifting behavior of PCDs as shown in Figure 11C. In the future, the solid-state luminescent PCDs will possibly achieve more breakthroughs in other types of solar cells. In terms of high-efficiency Si solar cells, although the down-conversion of graphene quantum dots (GQDs) with no solid-state fluorescence has been achieved,130 there’s still some room for improvement when employing the solid-state luminescent PCDs. 26


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Figure 11. The applications of quenching-resistant PCDs under solid state in solar cells, anti-counterfeiting and color-encoding. (A) Schematic architecture of the BHJ solar cells with luminescent down-shifting (LDS) layer. (B) J–V curves of the P3HT:PCBM-based BHJ solar cell with and without the LDS layer. (C) Wavelength dependences of EQE of the P3HT:PCBM-based solar cell with and without the LDS layer. Reproduced with permission of Elsevier from Ref 129. (D) Letters ‘‘ciomp’’ written on a common printing paper are invisible under daylight and even UV light, but appear when the UV light has just been turned off in a darkroom. Reproduced with permission of Royal Society of Chemistry from Ref 121. (E) Anti-counterfeiting applications of PCDs/PVA composites ink’s RTP in paper money. Reproduced with permission of Wiley-VCH from Ref 49. (F) Security protection applications of RTP property of PCDs. Reproduced with permission of American Chemical Society from Ref 50.

5.3 Other applications In addition to the photoelectric applications, the solid-state luminescent PCDs could be applied in other fields. Zhang’s group employed the as-synthesized PCDs as fingerprint detection tool based on solid-state fluorescent properties.92 In terms of the RTP properties of PCDs, it can be used as anti-counterfeiting ink and data-encryption applications, such as color-encoding and time-resolved identification. In 2013, Zhao’s group observed the RTP phenomenon of PCDs and applied it in anti-counterfeiting (Figure 11D).121 Similar modes (Figure 11E, F) were also reported by other groups.49-50 Qu’s group utilized water-induced photoluminescence behaviors of supra-PCDs for water-jet fluorescence printing and sweat pore imaging by water or sweat-induced PL of supra-PCDs/paper composites, which provided us a new 27



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application thoughts of PCDs in information storage, information security and protection and medical diagnose.74

6 CONCLUSIONS AND OUTLOOKS In summary, PCDs possess outstanding physicochemical properties, especially bright PL properties. In contrast with other light-emitting materials, PCDs exhibit some exact advantages including low toxicity, abundant raw material, simple preparation and post-treatment procedure, etc. Based on both experimental and theoretical results, the supramolecular crosslinking and SCEE are crucial in PCDs, with highly emphasizing great function in assisting efficient synthesis, mediating the PL behaviors and exploiting novel applications. However, we suppose that the supramolecular crosslinking-regulated emission in PCDs is still in its infant stage, and there are several crucial science problems to be solved, such as controllability of supramolecular crosslinking degree for further improving the optical properties, solid state

applications

exploitation

and

carrier

conductivity

improvement

for

optoelectronic applications. Currently, the supramolecualr crosslinking degree (intensity and types) is generally uncontrollable due to the hard characterization for supramolecular interaction. Thus, researchers couldn’t purposely obtain PCDs with certain optical and electrical properties by regulating the crosslinking degree (such as the size and orientation of supramolecular interaction, existed spatial position, etc.). Thus, the controllability of supramolecualr crosslinking degree may be a significant research direction in order to purposely gain the distinct PCDs with certain structures and properties. Especially, abundant supramolecular interaction types (such as hydrogen bonds, van der Waals interactions, host–guest interactions, and coordination interaction, etc.) could be employed for designing unique supramolecular crosslinking structure, which present an opportunity for the further development of PCDs. Taking the investigation of PCDs’ RTP for example, if the controllability of supramolecualr crosslinking degree is achieved, the RTP performances can be promoted and 28


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aqueous-state RTP can be obtained. The unique solid state emission renders PCDs potential in light-emitting applications. Currently, the investigation for PCDs’ solid-state emission is still preliminary stage. Increasing efforts are required to improve luminescent performances for high-performance applications, such as the study of related mechanisms, PL color regulation, the achievement of high PLQY, etc. More importantly, it is highly desired to broaden the application ranges based on unique solid state emission of PCDs in addition to the mentioned applications in this review. Finally, solid-state luminescent PCDs can probably make a breakthrough in electroluminescent light-emitting diodes fields as a result of more easy recombination between electron and hole, especially narrow-bandgap emission. However, the low carrier conductivity of PCDs may become a great obstacle, especially for long-chain alkyl containing PCDs and PCDs-based composites, which are detrimental to the transportation

of

carrier.

Thus,

in

order

to

achieve

high-performance

electroluminescent LEDs applications based on solid-state luminescent PCDs, it is highly urgent to develop strongly luminescent and self-quenching-resistant PCDs by rational synthesis design, with no long-chain alkyl-containing precursors or matrix employed to synthesize PCDs or combined with PCDs.

AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected] Notes The authors declare no competing financial interest

ACKNOWLEDGEMENT This work was financially supported by the National key research and development program of china (2016YFB0401701), the National Science Foundation of china (NSFC)

under

grant

Nos.

51433003,

51373065,

29


21504029

and


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JLU Science and Technology Innovative Research Team 2017TD-06.

REFERENCES (1) Qu, S.; Zhou, D.; Li, D.; Ji, W.; Jing, P.; Han, D.; Liu, L.; Zeng, H.; Shen, D. Toward Efficient Orange Emissive Carbon Nanodots through Conjugated sp2-Domain Controlling and Surface Charges Engineering. Adv. Mater. 2016, 28, 3516-3521. (2) Baker, S. N.; Baker, G. A. Luminescent Carbon Nanodots: Emergent Nanolights. Angew. Chem. Int. Ed. 2010, 49, 6726-6744. (3) Lim, S. Y.; Shen, W.; Gao, Z. Carbon Quantum Dots and Their Applications. Chem. Soc. Rev. 2015, 44, 362-381. (4) Yuan, F.; Li, S.; Fan, Z.; Meng, X.; Fan, L.; Yang, S. Shining Carbon Dots: Synthesis and Biomedical and Optoelectronic Applications. Nano Today 2016, 11, 565-586. (5) Song, Y.; Zhu, C.; Song, J.; Li, H.; Du, D.; Lin, Y. Drug-Derived Bright and Color-Tunable N-Doped Carbon Dots for Cell Imaging and Sensitive Detection of Fe3+ in Living Cells. ACS Appl. Mater. Interfaces 2017, 9, 7399-7405. (6) Zhu, A.; Qu, Q.; Shao, X.; Kong, B.; Tian, Y. Carbon-Dot-Based Dual-Emission Nanohybrid Produces a Ratiometric Fluorescent Sensor for in Vivo Imaging of Cellular Copper Ions. Angew. Chem. Int. Ed. 2012, 51, 7185-7189. (7) Song, Y.; Zhu, S.; Xiang, S.; Zhao, X.; Zhang, J.; Zhang, H.; Fu, Y.; Yang, B. Investigation into the Fluorescence Quenching Behaviors and Applications of Carbon Dots. Nanoscale 2014, 6, 4676-4682. (8) Ding, C.; Zhu, A.; Tian, Y. Functional Surface Engineering of C-Dots for Fluorescent Biosensing and in Vivo Bioimaging. Acc. Chem. Res. 2014, 47, 20-30. (9) Pan, L.; Sun, S.; Zhang, A.; Jiang, K.; Zhang, L.; Dong, C.; Huang, Q.; Wu, A.; Lin, H. Truly Fluorescent Excitation-Dependent Carbon Dots and Their Applications in Multicolor Cellular Imaging and Multidimensional Sensing. Adv. Mater. 2015, 27, 30


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7782-7787. (10) Qu, D.; Sun, Z.; Zheng, M.; Li, J.; Zhang, Y.; Zhang, G.; Zhao, H.; Liu, X.; Xie, Z. Three Colors Emission from S,N Co-Doped Graphene Quantum Dots for Visible Light H2 Production and Bioimaging. Adv. Optical Mater. 2015, 3, 360-367. 11. Liu, J.; Lu, S.; Tang, Q.; Zhang, K.; Yu, W.; Sun, H.; Yang, B. One-Step Hydrothermal Synthesis of Photoluminescent Carbon Nanodots with Selective Antibacterial Activity against Porphyromonas Gingivalis. Nanoscale 2017, 9, 7135-7142. (12) Zheng, M.; Ruan, S.; Liu, S.; Sun, T.; Qu, D.; Zhao, H.; Xie, Z.; Gao, H.; Jing, X.; Sun, Z. Self-Targeting Fluorescent Carbon Dots for Diagnosis of Brain Cancer Cells. ACS Nano 2015, 9, 11455-11461. (13) Feng, T.; Ai, X.; An, G.; Yang, P.; Zhao, Y. Charge-Convertible Carbon Dots for Imaging-Guided Drug Delivery with Enhanced in Vivo Cancer Therapeutic Efficiency. ACS Nano 2016, 10, 4410-4420. (14) Jian, H. J.; Wu, R. S.; Lin, T. Y.; Li, Y. J.; Lin, H. J.; Harroun, S. G.; Lai, J. Y.; Huang, C. C. Super-Cationic Carbon Quantum Dots Synthesized from Spermidine as an Eye Drop Formulation for Topical Treatment of Bacterial Keratitis. ACS Nano 2017, 11, 6703-6716. (15) Zheng, M.; Liu, S.; Li, J.; Qu, D.; Zhao, H.; Guan, X.; Hu, X.; Xie, Z.; Jing, X.; Sun, Z. Integrating Oxaliplatin With Highly Luminescent Carbon Dots: an Unprecedented Theranostic Agent for Personalized Medicine. Adv. Mater. 2014, 26, 3554-3560. (16) Wang, W.; Cheng, L.; Liu, W. Biological Applications of Carbon Dots. Science China Chemistry 2014, 57, 522-539. (17) Zhang, X.; Zhang, Y.; Wang, Y.; Kalytchuk, S.; Kershaw, S. V.; Wang, Y.; Wang, P.; Zhang, T.; Zhao, Y.; Zhang, H.; Cui, T.; Wang, Y.; Zhao, J.; Yu, W. W.; Rogach, A. L. Color-Switchable Electroluminescence of Carbon Dot Light-emitting Diodes. ACS 31



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nano 2013, 7, 11234-11241. (18) Yuan, F.; Wang, Z.; Li, X.; Li, Y.; Tan, Z.; Fan, L.; Yang, S. Bright Multicolor Bandgap Fluorescent Carbon Quantum Dots for Electroluminescent Light-Emitting Diodes. Adv. Mater. 2017, 29, 1604436. (19) Sun, C.; Zhang, Y.; Kalytchuk, S.; Wang, Y.; Zhang, X.; Gao, W.; Zhao, J.; Cepe, K.; Zboril, R.; Yu, W. W.; Rogach, A. L. Down-Conversion Monochromatic Light-Emitting Diodes with the Color Determined by the Active Layer Thickness and Concentration of Carbon Dots. J. Mater. Chem. C 2015, 3, 6613-6615. (20) Sun, M.; Qu, S.; Hao, Z.; Ji, W.; Jing, P.; Zhang, H.; Zhang, L.; Zhao, J.; Shen, D. Towards Efficient Solid-State Photoluminescence Based on Carbon-Nanodots and Starch Composites. Nanoscale 2014, 6, 13076-13081. (21) Liu, J.; Liu, Y.; Liu, N.; Han, Y.; Zhang, X.; Huang, H.; Lifshitz, Y.; Lee, S. T.; Zhong, J.; Kang, Z., Metal-Free Efficient Photocatalyst for Stable Visible Water Splitting via a Two-Electron Pathway. Science 2015, 347, 970-974. (22) Yu, H.; Shi, R.; Zhao, Y.; Waterhouse, G. I.; Wu, L. Z.; Tung, C. H.; Zhang, T. Smart Utilization of Carbon Dots in Semiconductor Photocatalysis. Adv. Mater. 2016, 28, 9454-9477. (23) Ye, K. H.; Wang, Z.; Gu, J.; Xiao, S.; Yuan, Y.; Zhu, Y.; Zhang, Y.; Mai, W.; Yang, S. Carbon Quantum Dots as a Visible Light Sensitizer to Significantly Increase the Solar Water Splitting Performance of Bismuth Vanadate Photoanodes. Energy Environ. Sci. 2017, 10, 772-779. (24) Fernando, K. A.; Sahu, S.; Liu, Y.; Lewis, W. K.; Guliants, E. A.; Jafariyan, A.; Wang, P.; Bunker, C. E.; Sun, Y. P. Carbon Quantum Dots and Applications in Photocatalytic Energy Conversion. ACS Appl. Mater. Interfaces 2015, 7, 8363-8376. (25) Qu, D.; Zheng, M.; Du, P.; Zhou, Y.; Zhang, L.; Li, D.; Tan, H.; Zhao, Z.; Xie, Z.; Sun, Z. Highly Luminescent S, N Co-Doped Graphene Quantum Dots with Broad Visible Absorption Bands for Visible Light Photocatalysts. Nanoscale 2013, 5, 32


Page 32 of 46

Page 33 of 46

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


12272-12277. (26) Briscoe, J.; Marinovic, A.; Sevilla, M.; Dunn, S.; Titirici, M. Biomass-Derived Carbon Quantum Dot Sensitizers for Solid-State Nanostructured Solar Cells. Angew. Chem. Int. Ed. 2015, 54, 4463-4468. (27) Lin, X.; Yang, Y.; Nian, L.; Su, H.; Ou, J.; Yuan, Z.; Xie, F.; Hong, W.; Yu, D.; Zhang, M.; Ma, Y.; Chen, X. Interfacial Modification Layers Based on Carbon Dots for Efficient Inverted Polymer Solar Cells Exceeding 10% Power Conversion Efficiency. Nano Energy 2016, 26, 216-223. (28) Liu, H.; He, Z.; Jiang, L. P.; Zhu, J. J. Microwave-Assisted Synthesis of Wavelength-Tunable Photoluminescent Carbon Nanodots and Their Potential Applications. ACS Appl. Mater. Interfaces 2015, 7, 4913-4920. (29) Liu, S. G.; Luo, D.; Li, N.; Zhang, W.; Lei, J. L.; Li, N. B.; Luo, H. Q. Water-Soluble Nonconjugated Polymer Nanoparticles with Strong Fluorescence Emission for Selective and Sensitive Detection of Nitro-Explosive Picric Acid in Aqueous Medium. ACS Appl. Mater. Interfaces 2016, 8, 21700-21709. (30) Lai, T.; Zheng, E.; Chen, L.; Wang, X.; Kong, L.; You, C.; Ruan, Y.; Weng, X. Hybrid Carbon Source for Producing Nitrogen-Doped Polymer Nanodots: One-Pot Hydrothermal Synthesis, Fluorescence Enhancement and Highly Selective Detection of Fe(III). Nanoscale 2013, 5, 8015-8021. (31) Miao, X.; Yan, X.; Qu, D.; Li, D.; Tao, F. F.; Sun, Z. Red Emissive Sulfur, Nitrogen Codoped Carbon Dots and Their Application in Ion Detection and Theraonostics. ACS Appl. Mater. Interfaces 2017, 9, 18549-18556. (32) Xu, X.; Zhang, K.; Zhao, L.; Li, C.; Bu, W.; Shen, Y.; Gu, Z.; Chang, B.; Zheng, C.; Lin, C.; Sun, H.; Yang, B. Aspirin-Based Carbon Dots, a Good Biocompatibility of Material Applied for Bioimaging and Anti-Inflammation. ACS Appl. Mater. Interfaces 2016, 8, 32706-32716. (33) Yuan, Y. H.; Liu, Z. X.; Li, R. S.; Zou, H. Y.; Lin, M.; Liu, H.; Huang, C. Z. 33



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 46

Synthesis of Nitrogen-Doping Carbon Dots with Different Photoluminescence Properties by Controlling the Surface States. Nanoscale 2016, 8, 6770-6776. (34) Liu, Y.; Duan, W.; Song, W.; Liu, J.; Ren, C.; Wu, J.; Liu, D.; Chen, H. Red Emission B, N, S-Co-Doped Carbon Dots for Colorimetric and Fluorescent Dual Mode Detection of Fe3+ Ions in Complex Biological Fluids and Living Cells. ACS Appl. Mater. Interfaces 2017, 9, 12663-12672. (35) Ge, J.; Jia, Q.; Liu, W.; Guo, L.; Liu, Q.; Lan, M.; Zhang, H.; Meng, X.; Wang, P. Red-Emissive Carbon Dots for Fluorescent, Photoacoustic, and Thermal Theranostics in Living Mice. Adv. Mater. 2015, 27, 4169-4177. (36) Zhang, J.; Yang, L.; Yuan, Y.; Jiang, J.; Yu, S. H. One-Pot Gram-Scale Synthesis of Nitrogen and Sulfur Embedded Organic Dots with Distinctive Fluorescence Behaviors in Free and Aggregated States. Chem. Mater. 2016, 28, 4367-4374. (37) Shi, L.; Yang, J. H.; Zeng, H. B.; Chen, Y. M.; Yang, S. C.; Wu, C.; Zeng, H.; Yoshihito, O.; Zhang, Q. Carbon Dots with High Fluorescence Quantum Yield: the Fluorescence

Originates

from

Organic

Fluorophores.

Nanoscale

2016,

8,

14374-14378. (38) Chen, Y.; Zheng, M.; Xiao, Y.; Dong, H.; Zhang, H.; Zhuang, J.; Hu, H.; Lei, B.; Liu, Y. A Self-Quenching-Resistant Carbon-Dot Powder with Tunable Solid-State Fluorescence and Construction of Dual-Fluorescence Morphologies for White Light-Emission. Adv. Mater. 2016, 28, 312-318. (39) Zhang, W.; Shi, L.; Liu, Y.; Meng, X.; Xu, H.; Xu, Y.; Liu, B.; Fang, X.; Li, H.-B.; Ding, T. Supramolecular Interactions via Hydrogen Bonding Contributing to Citric-Acid Derived Carbon Dots with High Quantum Yield and Sensitive Photoluminescence. RSC Adv. 2017, 7, 20345-20353. (40) Shih, C. C.; Chen, P. C.; Lin, G. L.; Wang, C. W.; Chang, H. T. Optical and Electrochemical

Applications

of

Silicon-Carbon

Nanocomposites. ACS Nano 2015, 9, 312-319. 34


Dots/Silicon

Dioxide

Page 35 of 46

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(41) Choi, Y.; Kang, B.; Lee, J.; Kim, S.; Kim, G. T.; Kang, H.; Lee, B. R.; Kim, H.; Shim, S. H.; Lee, G.; Kwon, O. H.; Kim, B. S. Integrative Approach toward Uncovering the Origin of Photoluminescence in Dual Heteroatom-Doped Carbon Nanodots. Chem. Mater. 2016, 28, 6840-6847. (42) Zhu, J.; Tang, Y.; Wang, G.; Mao, J.; Liu, Z.; Sun, T.; Wang, M.; Chen, D.; Yang, Y.; Li, J.; Deng, Y.; Yang, S. Green, Rapid, and Universal Preparation Approach of Graphene Quantum Dots under Ultraviolet Irradiation. ACS Appl. Mater. Interfaces 2017, 9, 14470-14477. (43) Guo, L.; Ge, J.; Liu, W.; Niu, G.; Jia, Q.; Wang, H.; Wang, P. Tunable Multicolor Carbon Dots Prepared from Well-Defined Polythiophene Derivatives and Their Emission Mechanism. Nanoscale 2016, 8, 729-734. (44) Wu, M.; Zhan, J.; Geng, B.; He, P.; Wu, K.; Wang, L.; Xu, G.; Li, Z.; Yin, L.; Pan, D. Scalable Synthesis of Organic-Soluble Carbon Quantum Dots: Superior Optical Properties in Solvents, Solids, and LEDs. Nanoscale 2017, 9, 13195-13202. (45) Zhang, Z.; Pan, Y.; Fang, Y.; Zhang, L.; Chen, J.; Yi, C. Tuning Photoluminescence and Surface Properties of Carbon Nanodots for Chemical Sensing. Nanoscale 2016, 8, 500-507. (46) Kwon, W.; Do, S.; Kim, J. H.; Seok Jeong, M.; Rhee, S. W. Control of Photoluminescence of Carbon Nanodots via Surface Functionalization using Para-Substituted Anilines. Sci. Rep. 2015, 5, 12604. (47) Liu, J.; Ning Wang.; Yu, Y.; Yan, Y.; Zhang, H.; Li, J.; Yu, J. Carbon Dots in Zeolites: A New Class of Thermally Activated Delayed Fluorescence Materials with Ultralong Lifetimes. Sci. Adv. 2017, 3, 1603171. (48) Chen, H.; Wang, G. D.; Sun, X.; Todd, T.; Zhang, F.; Xie, J.; Shen, B. Mesoporous Silica as Nanoreactors to Prepare Gd-Encapsulated Carbon Dots of Controllable Sizes and Magnetic Properties. Adv. Funct. Mater. 2016, 26, 3973-3982. (49) Jiang, K.; Zhang, L.; Lu, J.; Xu, C.; Cai, C.; Lin, H. Triple-mode Emission of 35



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Carbon Dots: Applications for Advanced Anti-Counterfeiting. Angew. Chem. Int. Ed. 2016, 55, 7231-7235. (50) Li, Q.; Zhou, M.; Yang, Q.; Wu, Q.; Shi, J.; Gong, A.; Yang, M. Efficient Room-Temperature Phosphorescence from Nitrogen-Doped Carbon Dots in Composite Matrices. Chem. Mater. 2016, 28, 8221-8227. (51) Zhang, T.; Zhu, J.; Zhai, Y.; Wang, H.; Bai, X.; Dong, B.; Wang, H.; Song, H. A Novel Mechanism for Red Emission Carbon Dots: Hydrogen Bond Dominated Molecular States Emission. Nanoscale 2017, 9, 13042-13051. (52) Gude, V.; Das, A.; Chatterjee, T.; Mandal, P. K. Molecular Origin of Photoluminescence of Carbon Dots: Aggregation-Induced Orange-Red Emission. Phys. Chem. Chem. Phys. 2016, 18, 28274-28280. (53) Hong, Y.; Lam, J. W. Y.; Tang, B. Z. Aggregation-Induced Emission. Chem. Soc. Rev. 2011, 40, 5361-5388. (54) Hong, Y.; Lam, J. W.; Tang, B. Z. Aggregation-Induced Emission: Phenomenon, Mechanism and Applications. Chem. Commun. 2009, 45, 4332-4353. (55) Mei, J.; Leung, N. L.; Kwok, R. T.; Lam, J. W.; Tang, B. Z. Aggregation-Induced Emission: Together We Shine, United We Soar! Chem. Rev. 2015, 115, 11718-11940. (56) Zhu, S.; Song, Y.; Shao, J.; Zhao, X.; Yang, B. Non-Conjugated Polymer Dots with Crosslink-Enhanced Emission in the Absence of Fluorophore Units. Angew. Chem. Int. Ed. 2015, 54, 14626-14637. (57) Zhu, S.; Wang, L.; Zhou, N.; Zhao, X.; Song, Y.; Maharjan, S.; Zhang, J.; Lu, L.; Wang, H.; Yang, B. The Crosslink Enhanced Emission (CEE) in Non-Conjugated Polymer Dots: from the Photoluminescence Mechanism to the Cellular Uptake Mechanism and Internalization. Chem. Commun. 2014, 50, 13845-13848. (58) Tao, S.; Zhu, S.; Feng, T.; Xia, C.; Song, Y.; Yang, B. The Polymeric Characteristics and Photoluminescence Mechanism in Polymer Carbon Dots: A Review. Materials Today Chemistry 2017, 6, 13-25. 36


Page 36 of 46

Page 37 of 46

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(59) Tao, S.; Song, Y.; Zhu, S.; Shao, J.; Yang, B. A New Type of Polymer Carbon Dots with High Quantum Yield: From Synthesis to Investigation on Fluorescence Mechanism. Polymer 2017, 116, 472-478. (60) Tong, D.; Li, W.; Zhao, Y.; Zhang, L.; Zheng, J.; Cai, T.; Liu, S. Non-Conjugated Polyurethane Polymer Dots Based on Crosslink Enhanced Emission (CEE) and Application in Fe3+ Sensing. RSC Adv. 2016, 6, 97137-97141. (61) Liu, S. G.; Liu, T.; Li, N.; Geng, S.; Lei, J. L.; Li, N. B.; Luo, H. Q. Polyethylenimine-Derived Fluorescent Nonconjugated Polymer Dots with Reversible Dual-Signal pH Response and Logic Gate Operation. J. Phys. Chem. C 2017, 121, 6874-6883. (62) Bhattacharya, A.; Das, S.; Mukherjee, T. K. Insights into the Thermodynamics of Polymer Nanodot-Human Serum Albumin Association: A Spectroscopic and Calorimetric Approach. Langmuir 2016, 32, 12067-12077. (63) Yang, J.; Zhang, Y.; Gautam, S.; Liu, L.; Dey, J.; Chen, W.; Mason, R. P.; Serrano, C. A.; Schug, K. A.; Tang, L. Development of Aliphatic Biodegradable Photoluminescent Polymers. Proc. Natl. Acad. Sci. 2009, 106, 10086-10091. (64) Sun, Y.; Cao, W.; Li, S.; Jin, S.; Hu, K.; Hu, L.; Huang, Y.; Gao, X.; Wu, Y.; Liang,

X.

J.

Ultrabright

and Multicolorful Fluorescence

of

Amphiphilic

Polyethyleneimine Polymer Dots for Efficiently Combined Imaging and Therapy. Sci. Rep. 2013, 3, 3036. (65) Li, J.; Yu, X.; Wang, Y.; Yuan, Y.; Xiao, H.; Cheng, D.; Shuai, X. A Reduction and pH Dual-Sensitive Polymeric Vector for Long-Circulating and Tumor-Targeted siRNA Delivery. Adv. Mater. 2014, 26, 8217-8224. (66) Guo, C. X.; Xie, J.; Wang, B.; Zheng, X.; Yang, H. B.; Li, C. M. A new Class of Fluorescent-Dots: Long Luminescent Lifetime Bio-Dots Self-Assembled from DNA at Low Temperatures. Sci. Rep. 2013, 3, 2957. (67) Zhu, S.; Meng, Q.; Wang, L.; Zhang, J.; Song, Y.; Jin, H.; Zhang, K.; Sun, H.; 37



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Wang, H.; Yang, B. Highly Photoluminescent Carbon Dots for Multicolor Patterning, Sensors, and Bioimaging. Angew. Chem. Int. Ed.2013, 52, 3953-3957. (68) Lu, S.; Cong, R.; Zhu, S.; Zhao, X.; Liu, J.; Tse, J. S.; Meng, S.; Yang, B. pH-Dependent Synthesis of Novel Structure-Controllable Polymer-Carbon NanoDots with High Acidophilic Luminescence and Super Carbon Dots Assembly for White Light-Emitting Diodes. ACS Appl. Mater. Interfaces 2016, 8, 4062–4068. (69) Lu, S.; Zhao, X.; Zhu, S.; Song, Y.; Yang, B. Novel Cookie-with-Chocolate Carbon Dots Displaying Extremely Acidophilic High Luminescence. Nanoscale 2014, 6, 13939-13944. (70) Vedamalai, M.; Periasamy, A. P.; Wang, C. W.; Tseng, Y. T.; Ho, L. C.; Shih, C. C.; Chang, H. T. Carbon Nanodots Prepared from O-Phenylenediamine for Sensing of Cu2+ Ions in Cells. Nanoscale 2014, 6, 13119-13125. (71) Krysmann, M. J.; Kelarakis, A.; Dallas, P.; Giannelis, E. P. Formation Mechanism of Carbogenic Nanoparticles with Dual Photoluminescence Emission. J. Am. Chem. Soc. 2012, 134, 747-750. (72) Song, Y.; Zhu, S.; Zhang, S.; Fu, Y.; Wang, L.; Zhao, X.; Yang, B. Investigation from Chemical Structure to Photoluminescent Mechanism: a Type of Carbon Dots from the Pyrolysis of Citric Acid and an Amine. J. Mater. Chem. C 2015, 3, 5976-5984. (73) Zhu, S.; Zhao, X.; Song, Y.; Lu, S.; Yang, B. Beyond Bottom-up Carbon Nanodots: Citric-Acid Derived Organic Molecules. Nano Today 2016, 11, 128-132. (74) Lou, Q.; Qu, S.; Jing, P.; Ji, W.; Li, D.; Cao, J.; Zhang, H.; Liu, L.; Zhao, J.; Shen, D. Water-Triggered Luminescent "Nano-Bombs" Based on Supra-(Carbon Nanodots). Adv. Mater. 2015, 27, 1389-1394. (75) Wang, H.; Sun, C.; Chen, X.; Zhang, Y.; Colvin, V. L.; Rice, Q.; Seo, J.; Feng, S.; Wang, S.; Yu, W. W. Excitation Wavelength Independent Visible Color Emission of Carbon Dots. Nanoscale 2017, 9, 1909-1915. 38


Page 38 of 46

Page 39 of 46

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(76) Ding, H.; Yu, S. B.; Wei, J. S.; Xiong, H. M. Full-Color Light-Emitting Carbon Dots with a Surface-State-Controlled Luminescence Mechanism. ACS Nano 2016, 10, 484-491. (77) Chen, X.; Jin, Q.; Wu, L.; Tung, C.; Tang, X. Synthesis and Unique Photoluminescence Properties of Nitrogen-Rich

Quantum Dots and

Their

Applications. Angew. Chem. Int. Ed. 2014, 53, 12542-12547. (78) Wang, Z.; Yuan, F.; Li, X.; Li, Y.; Zhong, H.; Fan, L.; Yang, S. 53% Efficient Red Emissive Carbon Quantum Dots for High Color Rendering and Stable Warm White-Light-Emitting Diodes. Adv Mater 2017, 29, 1702910. (79) Jiang, K.; Sun, S.; Zhang, L.; Lu, Y.; Wu, A.; Cai, C.; Lin, H. Red, Green, and Blue Luminescence by Carbon Dots: Full-Color Emission Tuning and Multicolor Cellular Imaging. Angew. Chem. Int. Ed. 2015, 54, 5360-5363. (80) Lu, S. Y.; Yang, B. One Step Synthesis of Efficient Orange-Red Emissive Polymer Carbon Nanodots Displaying Unexpect Two Photon Fluorescence. Acta Polymerica Sinica 2017, 7, 1200-1206. (81) Qu, D.; Zheng, M.; Li, J.; Xie, Z.; Sun, Z., Tailoring Color Emissions from N-Doped Graphene Quantum Dots for Bioimaging Applications. Light: Science & Applications 2015, 4, e364. (82) Zhang, Y.; Yuan, R.; He, M.; Hu, G.; Jiang, J.; Xu, T.; Zhou, L.; Chen, W.; Xiang, W.; Liang, X. Multicolour Nitrogen-Doped Carbon: Tuneable Photoluminescence and Sandwich Fluorescent Glass-Based Light-Emitting Diodes. Nanoscale 2017, 10.1039/C7NR05363K. (83) Tian, Z.; Zhang, X.; Li, D.; Zhou, D.; Jing, P.; Shen, D.; Qu, S.; Zboril, R.; Rogach, A. L. Full-Color Inorganic Carbon Dot Phosphors for White-Light-Emitting Diodes. Adv. Optical Mater. 2017, 5, 1700416. (84) Hu, S.; Trinchi, A.; Atkin, P.; Cole, I. Tunable Photoluminescence Across the Entire Visible Spectrum from Carbon Dots Excited by White Light. Angew. Chem. Int. 39



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 40 of 46

Ed. 2015, 54, 2970-2974. (85) Meng, X.; Chang, Q.; Xue, C.; Yang, J.; Hu, S. Full-colour Carbon Dots: from Energy-Efficient

Synthesis

to

Concentration-Dependent

Photoluminescence

Properties. Chem. Commun. 2017, 53, 3074-3077. (86) Mao, Q. X.; E, S.; Xia, J. M.; Song, R. S.; Shu, Y.; Chen, X. W.; Wang, J. H. Hydrophobic Carbon Nanodots with Rapid Cell Penetrability and Tunable Photoluminescence Behavior for in Vitro and in Vivo Imaging. Langmuir 2016, 32, 12221-12229. (87) Mu, Y.; Wang, N.; Sun, Z.; Wang, J.; Li, J.; Yu, J. Carbogenic Nanodots Derived from Organo-Templated Zeolites with Modulated Full-Color Luminescence. Chem. Sci. 2016, 7, 3564-3568. (88) Chen, X.; Bai, X.; Sun, C.; Su, L.; Wang, Y.; Zhang, Y.; Yu, W. W. High Efficient Light-Emitting Diodes Based on Liquid-Type Carbon Dots. RSC Adv. 2016, 6, 96798-96802. (89) Shao, J.; Zhu, S.; Liu, H.; Song, Y.; Tao, S.; Yang, B. Full-Color Emission Polymer Carbon Dots with Quench-Resistant Solid-State Fluorescence. Adv. Sci. 2017, 1700395. (90) Chiang, C. L.; Wu, M. F.; Dai, D. C.; Wen, Y. S.; Wang, J. K.; Chen, C. T. Red-Emitting Fluorenes as Efficient Emitting Hosts for Non-Doped, Organic Red-Light-Emitting Diodes. Adv. Funct. Mater. 2005, 15, 231-238. (91) Ooyama, Y.; Yoshikawa, S.; Watanabe, S.; Yoshida, K. Molecular Design of Novel Non-Planar Heteropolycyclic

Fluorophores

with Bulky Substituents:

Convenient Synthesis and Solid-State Fluorescence Characterization. Org. Biomol. Chem. 2006, 4, 3406-3409. (92) Xu, M.; He, G.; Li, Z.; He, F.; Gao, F.; Su, Y.; Zhang, L.; Yang, Z.; Zhang, Y. A Green

Heterogeneous

Synthesis

of

N-Doped

Carbon

Dots

and

Their

Photoluminescence Applications in Solid and Aqueous States. Nanoscale 2014, 6, 40


Page 41 of 46

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


10307-10315. (93) Zhang, Y.; Li, C.; Fan, Y.; Wang, C.; Yang, R.; Liu, X.; Zhou, L. A Self-Quenching-Resistant Carbon Nanodot Powder with Multicolored Solid-State Fluorescence for Ultra-Fast Staining of Various Representative Bacterial Species within one Minute. Nanoscale 2016, 8, 19744-19753. (94) Guo, X.; Wang, C. F.; Yu, Z. Y.; Chen, L.; Chen, S. Facile Access to Versatile Fluorescent Carbon Dots toward Light-Emitting Diodes. Chem. Commun. 2012, 48, 2692-2694. (95) Mao, L. H.; Tang, W. Q.; Deng, Z.-Y.; Liu, S. S.; Wang, C.-F.; Chen, S. Facile Access to White Fluorescent Carbon Dots toward Light-Emitting Devices. Industrial & Engineering Chemistry Research 2014, 53, 6417-6425. (96) Li, X.; Liu, Y.; Song, X.; Wang, H.; Gu, H.; Zeng, H. Intercrossed Carbon Nanorings with Pure Surface States as Low-Cost and Environment-Friendly Phosphors for White-Light-Emitting Diodes. Angew. Chem. Int. Ed. 2015, 54, 1759-1764. (97) Wang, F.; Xie, Z.; Zhang, H.; Liu, C. Y.; Zhang, Y. G. Highly Luminescent Organosilane-Functionalized Carbon Dots. Adv. Funct. Mater. 2011, 21, 1027-1031. (98) Xie, Z.; Wang, F.; Liu, C. Y. Organic-Inorganic Hybrid Functional Carbon Dot Gel Glasses. Adv. Mater. 2012, 24, 1716-1721. (99) Chen, P. C.; Chen, Y. N.; Hsu, P. C.; Shih, C. C.; Chang, H. T. Photoluminescent Organosilane-Functionalized Carbon Dots as Temperature Probes. Chem. Commun. 2013, 49, 1639-1641. (100) Zhang, F.; Feng, X.; Zhang, Y.; Yan, L.; Yang, Y.; Liu, X. Photoluminescent Carbon Quantum Dots as a Directly Film-Forming Phosphor towards White LEDs. Nanoscale 2016, 8, 8618-8632. (101) Zheng, J.; Wang, Y.; Zhang, F.; Yang, Y.; Liu, X.; Guo, K.; Wang, H.; Xu, B. Microwave-Assisted Hydrothermal Synthesis of Solid-State Carbon Dots with 41



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Intensive Emission for White Light-Emitting Devices. J. Mater. Chem. C 2017, 5, 8105-8111. (102) He, J.; He, Y.; Chen, Y.; Lei, B.; Zhuang, J.; Xiao, Y.; Liang, Y.; Zheng, M.; Zhang, H.; Liu, Y. Solid-State Carbon Dots with Red Fluorescence and Efficient Construction of Dual-Fluorescence Morphologies. Small 2017, 13, 1700075. (103) Wang, Y.; Wang, K.; Han, Z.; Yin, Z.; Zhou, C.; Du, F.; Zhou, S.; Chen, P.; Xie, Z. High Color Rendering Index Trichromatic White and Red LEDs Prepared from Silane-Functionalized Carbon Dots. J. Mater. Chem. C 2017, 5, 9629-9637. (104) Zhang, H.; Liu, Y.; Yao, D.; Yang, B. Hybridization of Inorganic Nanoparticles and Polymers to Create Regular and Reversible Self-Assembly Architectures. Chem. Soc. Rev. 2012, 41, 6066-6088. (105) Wang, Z.; Susha, A. S.; Chen, B.; Reckmeier, C.; Tomanec, O.; Zboril, R.; Zhong, H.; Rogach, A. L. Poly(vinylpyrrolidone) Supported Copper Nanoclusters: Glutathione Enhanced Blue Photoluminescence for Application in Phosphor Converted Light Emitting Devices. Nanoscale 2016, 8, 7197-7202. (106) Zheng, X. G.; Wang, H. L.; Ding, G. Q.; Cui, G. L.; Chen, L.; Zhang, P. H.; Gong, Q.; Wang, S. M. Facile Synthesis of Highly Graphitized Nitrogen-Doped Carbon Dots and Carbon Sheets with Solid-State White-Light Emission. Materials Letters 2017, 195, 58-61. (107) Wang, Y.; Zhao, Y.; Zhang, F.; Chen, L.; Yang, Y.; Liu, X. Fluorescent Polyvinyl Alcohol Films Based on Nitrogen and Sulfur Co-Doped Carbon Dots towards White Light-Emitting Devices. New J. Chem. 2016, 40, 8710-8716. (108) Zhu, S.; Zhang, J.; Song, Y.; Zhang, G.; Zhang, H.; Yang, B. Fluorescent Nanocomposite Based on PVA Polymer Dots. Acta Chimica Sinica 2012, 70, 2311-2315. (109) Chen, Q. L.; Wang, C. F.; Chen, S. One-Step Synthesis of Yellow-Emitting Carbogenic Dots toward White Light-Emitting Diodes. J. Mater. Sci. 2013, 48, 42


Page 42 of 46

Page 43 of 46

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2352-2357. (110) Kwon, W.; Do, S.; Lee, J.; Hwang, S.; Kim, J. K.; Rhee, S. W. Freestanding Luminescent Films of Nitrogen-Rich Carbon Nanodots toward Large-Scale Phosphor-Based White-Light-Emitting Devices. Chem. Mater. 2013, 25, 1893-1899. (111) Do, S.; Kwon, W.; Rhee, S. W. Soft-Template Synthesis of Nitrogen-Doped carbon Nanodots: Tunable Visible-Light Photoluminescence and Phosphor-Based Light-Emitting Diodes. J. Mater. Chem. C 2014, 2, 4221-4226. (112) Kwon, W.; Lee, G.; Do, S.; Joo, T.; Rhee, S. W. Size-Controlled Soft-Template Synthesis of Carbon Nanodots toward Versatile Photoactive Materials. Small 2014, 10, 506-513. (113) Zhang, W.; Yu, S. F.; Fei, L.; Jin, L.; Pan, S.; Lin, P. Large-Area Color Controllable Remote Carbon White-Light Light-Emitting Diodes. Carbon 2015, 85, 344-350. (114) Li, X.; Zhang, S.; Kulinich, S. A.; Liu, Y.; Zeng, H. Engineering Surface States of Carbon Dots to Achieve Controllable Luminescence for Solid-Luminescent Composites and Sensitive Be2+ Detection. Sci. Rep. 2014, 4, 4978. (115) Bhunia, S. K.; Nandi, S.; Shikler, R.; Jelinek, R. Tuneable Light-Emitting Carbon-Dot/Polymer Flexible Films Prepared through One-Pot Synthesis. Nanoscale 2016, 8, 3400-3406. (116) Wang, Y.; Kalytchuk, S.; Wang, L.; Zhovtiuk, O.; Cepe, K.; Zboril, R.; Rogach, A.

L.

Carbon

Dot

Hybrids

with

Oligomeric

Silsesquioxane:

Solid-State

Luminophores with High Photoluminescence Quantum Yield and Applicability in White Light Emitting Devices. Chem. Commun. 2015, 51, 2950-2953. (117) Zhou, D.; Li, D.; Jing, P.; Zhai, Y.; Shen, D.; Qu, S.; Rogach, A. L. Conquering Aggregation-Induced Solid-State Luminescence Quenching of Carbon Dots through a Carbon Dots-Triggered Silica Gelation Process. Chem. Mater. 2017, 29, 1779-1787. (118) Zhai, Y.; Zhou, D.; Jing, P.; Li, D.; Zeng, H.; Qu, S. Preparation and Application 43



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 44 of 46

of Carbon-Nanodot@NaCl Composite Phosphors with Strong Green Emission. J. Colloid Interface Sci. 2017, 497, 165-171. (119) Kim, T. H.; Wang, F.; McCormick, P.; Wang, L.; Brown, C.; Li, Q. Salt-Embedded Carbon Nanodots as a UV and Thermal Stable Fluorophore for Light-Emitting Diodes. Journal of Luminescence 2014, 154, 1-7. (120) Zhou, D.; Zhai, Y.; Qu, S.; Li, D.; Jing, P.; Ji, W.; Shen, D.; Rogach, A. L. Electrostatic

Assembly

Guided

Synthesis

of

Highly

Luminescent

Carbon-Nanodots@BaSO4 Hybrid Phosphors with Improved Stability. Small 2017, 13, 1602055. (121) Deng, Y.; Zhao, D.; Chen, X.; Wang, F.; Song, H.; Shen, D. Long Lifetime Pure Organic Phosphorescence Based on Water Soluble Carbon Dots. Chem. Commun. 2013, 49, 5751-5753. (122) Tan, J.; Zhang, J.; Li, W.; Zhang, L.; Yue, D. Synthesis of Amphiphilic Carbon Quantum Dots with Phosphorescence Properties and Their Multifunctional Applications. J. Mater. Chem. C 2016, 4, 10146-10153. (123) Tan, J.; Zou, R.; Zhang, J.; Li, W.; Zhang, L.; Yue, D. Large-Scale Synthesis of N-Doped Carbon Quantum Dots and Their Phosphorescence Properties in a Polyurethane Matrix. Nanoscale 2016, 8, 4742-4747. (124) Chen, Y.; He, J.; Hu, C.; Zhang, H.; Lei, B.; Liu, Y. Room Temperature Phosphorescence

from

Moisture-Resistant

and

Oxygen-Barred

Carbon

Dot

Aggregates. J. Mater. Chem. C 2017, 5, 6243-6250. (125) Bai, L. Q.; Xue, N.; Wang, X. R.; Shi, W. Y.; Lu, C. Activating Efficient Room Temperature Phosphorescence of Carbon Dots by Synergism of Orderly Non-Noble Metals and Dual Structural Confinements. Nanoscale 2017, 9, 6658-6664. (126) Dong, X.; Wei, L.; Su, Y.; Li, Z.; Geng, H.; Yang, C.; Zhang, Y. Efficient Long Lifetime Room Temperature Phosphorescence of Carbon Dots in a Potash Alum Matrix. J. Mater. Chem. C 2015, 3, 2798-2801. 44


Page 45 of 46

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(127) Sun, C.; Zhang, Y.; Sun, K.; Reckmeier, C.; Zhang, T.; Zhang, X.; Zhao, J.; Wu, C.; Yu, W. W.; Rogach, A. L. Combination of Carbon Dot and Polymer Dot Phosphors for White Light-Emitting Diodes. Nanoscale 2015, 7, 12045-12050. (128) Chen, Y.; Lei, B.; Zheng, M.; Zhang, H.; Zhuang, J.; Liu, Y. A Dual-Emitting Core-Shell Carbon Dot-Silica-Phosphor Composite for White Light Emission. Nanoscale 2015, 7 , 20142-20148. (129) Huang, J. J.; Zhong, Z. F.; Rong, M. Z.; Zhou, X.; Chen, X. D.; Zhang, M. Q. An Easy Approach of Preparing Strongly Luminescent Carbon Dots and Their Polymer Based Composites for Enhancing Solar Cell Efficiency. Carbon 2014, 70, 190-198. (130) Tsai, M. L.; Tu, W. C.; Tang, L.; Wei, T. C.; Wei, W. R.; Lau, S. P.; Chen, L. J.; He, J. H. Efficiency Enhancement of Silicon Heterojunction Solar Cells via Photon Management Using Graphene Quantum Dot as Downconverters. Nano Lett. 2016, 16, 309-313.

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TOC Figure

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Supramolecular Cross-Link-Regulated Emission and Related

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