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Aggregation-Induced Enhanced Electrochemiluminescence from Organic Nanoparticles of Donor-Acceptor Based Coumarin Derivatives Huiwen Liu, Lifen Wang, Hongfang Gao, Honglan Qi, Qiang Gao, and Chengxiao Zhang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b15434 • Publication Date (Web): 24 Nov 2017 Downloaded from http://pubs.acs.org on November 26, 2017

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ACS Applied Materials & Interfaces

Aggregation-Induced Enhanced Electrochemiluminescence from Organic Nanoparticles of Donor-Acceptor Based Coumarin Derivatives Huiwen Liu, Lifen Wang, Hongfang Gao, Honglan Qi*, Qiang Gao, Chengxiao Zhang Key Laboratory of Applied Surface and Colloid Chemistry (Ministry of Education), School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi’an, 710062, PR China

Keywords:

Electrochemiluminescence;

Coumarin

derivative;

Donor-acceptor;

Organic nanoparticles; Aggregation

*Corresponding author. Tel.: +86-29-81530726; Fax: +86-29-81530727. E-mail: [email protected]. 1

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Abstract: Organic nanoparticles (NPs) from donor-acceptor based coumarin derivatives, 6-[4-(N,N-diphenylamino)phenyl] -3-ethoxycarbonyl coumarin (DPA-CM), with an average size of 5.82 nm, were synthesized by a facile reprecipitation method using water as a poor solvent and tetrahydrofuran as a good solvent. Red-shifted absorption, blue-shifted

photoluminescence

emission

and

aggregation-induced

enhanced

electrochemiluminescence (ECL) emission were observed for the DPA-CM NPs in aqueous solution compared with the original DPA-CM in organic solution. The aggregation-induced enhanced ECL emission is ascribed to the combined effects of the small size of the DPA-CM NPs, the restricted conformational relaxation in the NPs and the good stability of the cationic radical of DPA-CM. A strong and stable ECL emission is obtained at the DPA-CM NPs modified glassy carbon electrode in the presence of tri-n-propylamine and the ECL intensity of the DPA-CM NPs modified electrode is quenched linearly in the range of 0.05 µM to 50 µM with detection limit of 0.04 µM, 0.2 µM and 0.4 µM for ascorbic acid, uric acid and dopamine, respectively. This work shows an example of donor-acceptor based organic NPs as ECL emitters and their analytical applications to monitor biomolecules.

2


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INTRODUCTION Electrochemiluminescence (ECL), the process whereby emission is generated from electrochemically generated reagents, has received ever-increasing interest due to its high sensitivity and low background in a wide range of applications.1-4 Three types of ECL luminophores, i.e., inorganic molecules (Ru(bpy)32+

5

), organic

molecules (luminol 6 ) and nanomaterials (quantum dots 7 ) have been extensively exploited. Among them, nanomaterials, especially organic nanoparticles (NPs), as a new type of ECL emitter, are attracting increasing interest due to the large number of molecular structures and the flexibility and diversity in synthetic strategies. 8 Additionally, the ECL of organic NPs provides the possibility of potential applications in bio-analysis because of the low toxicity and the good suspension of the NPs in aqueous solution. Some studies have reported the ECL of organic NPs, including organic compounds (e.g., 9,10-diphenylanthracene (DPA) nanorods and rubrene nanoparticles, 9 9-naphthylanthracene derivatives nanoparticles, 10 rubrene single nanoparticles, oligothiophene

11

9,10-bis(phenylethynyl)anthracene nanoparticles

13

),

poly(9,9-dioctylfluorene-co-benzothiadiazole,

and

(BPA)

organic

F8BT)

nanoparticles, polymers

nanoparticles,

14

12

(e.g., poly

[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] conjugated polymer dots,15 poly(9,9-dioctylfluorene) nanowires, 16 and silole-containing polymer nanodot 17 ). Although these organic nanomaterials can generate ECL signals, certain challenges, such as the large size of the nanoparticles and solid fluorescence quenching issues, limit their analytical applications. Apart from the detection of tri-n-propylamine (TPA) and creatinine using BPA nanoparticles12 and the detection of dopamine using silole-containing polymer nanodot,17 few analytical applications have been examined. Much effort has been expended to synthesize small organic nanoparticles and to 3



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improve the photoluminescence quantum yield of organic nanoparticles. Many techniques (such as reprecipitation,9-16 ultra-sonication, 18 microemulsion 19 and chemical reactions20) have been used to synthesize organic nanomaterials with various shapes and sizes. Among them, the reprecipitation method has received extra attention because of its cost-effectiveness, in which a small volume of the target in the “good” solvent was injected into a larger volume of “poor” solvent.8 A low concentration or small volume of the target in good solvent is favorable towards creating smaller nanoparticles.

Molecules

with

aggregation-induced

emission

(AIE)

or

aggregation-induced emission enhancement (AIEE) have attracted increasing attention because of their high emission efficiencies in the aggregated states.21 Many AIE molecules (such as tetraphenylethene, hexaphenylsilole and distyreneanthracene, polyacetylenes, poly(phenyleneethylene)s and polytriazoles) have been reported and used in fluorescence sensing, bio-imaging and optical devices.22,23 For example, a fluorescent chemosensor was developed for the detection of picric acid in the aggregate and solid states by using TPE-containing polytriazole as an emitter.24 A multilayer OLED, using AIE-active silole derivatives in the light-emitting layer, shows good performance with a maximum luminance of 27070 cd m-2 and a maximum current efficiency of 10.23 cd A-1. 25 To our best knowledge, one aggregation-induced ECL from platinum (II) complex was just reported by Hogan’s group.26 However, there is no report on the AIE or AIEE of organic dyes for ECL in aqueous solution and ECL bioassays. Donor-acceptor (D-A) conjugated molecules have been recognized as promising molecules in organic light-emitting diodes, organic photovoltaic devices, 27 and fluorescence imaging.28 Few ECL studies of D-A conjugated molecule NPs (AzideBTA, 29 dithienylbenzothiadiazole-based donor-acceptor-donor red fluorophore, 30 4


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spiro-BTA31) have been reported. The research reveals that the photophysical and electrochemical

properties

(the

photoluminescence

quantum

yield,

the

electrochemical stability, and ECL efficiency) are strongly dependent on the donors and acceptors, and the nanoparticle size and shape.31,

32

Coumarin and its derivatives

are of great interest as good electron acceptors in biological and medical applications due to their good biological activity33 as well as in organic light-emitting devices because of its high photoluminescence quantum yields.34 Some ECL emitters of coumarin

derivatives

have

arylamino-substituted coumarin,

been 36

reported,

including

coumarin

30,

donor-substituted phenylethynylcoumarins,

35

37

three different coumarin derivatives, 38 Europium (III) complex with coumarin 3-carboxylic acid,39 and N-coumarin derivatives.40 Despite the remarkable properties and uses of coumarin derivatives, to the best of our knowledge, there is no report on the ECL of organic nanoparticles made from coumarin derivatives in aqueous solution. Inspired by developing highly efficient and stable ECL organic nanoparticles, particularly for the purpose as an analytical application, we report the synthesis of organic

nanoparticles

with

an

average

size

of

5.82

nm

from

6-[4-(N,N-diphenylamino)phenyl]-3-ethoxycarbonyl coumarin (DPA-CM), as a donor-acceptor

compound

with

fine

photoelectric

properties.

41

A

facile

reprecipitation method was adopted for the fabrication of DPA-CM nanoparticles (DPA-CM NPs). The synthesized DPA-CM NPs display a strong and stable anodic ECL emission using TPA as a coreactant, which is promising as an effective ECL emitter. Based on the ECL quenching of the DPA-CM NPs by ascorbic acid, uric acid or dopamine (Scheme 1), three biomolecules that exist in human blood or urine, analytical application of the DPA-CM NPs in the detection of three quencher-related 5



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molecules was illustrated with high sensitivity and a low detection limit. Preferred position for Scheme 1. EXPERIMENTAL Materials.

6-[4-(N,N-diphenylamino)phenyl]-3-ethoxycarbonyl

coumarin

(DPA-CM) (C30H23NO4, Exact Mass: 461.18, DPA-CM, chemical structure is shown in Scheme 1) was obtained from Tokyo Chemical Industry Co., Ltd. (China). Tri-n-propylamine (TPA) was obtained from Sinopharm Chemical Reagent Co., Ltd. (China). Ascorbic acid (AA) was obtained from Aladdin biochemical technology Co., Ltd (China). Uric acid (UA) was purchased from Tianda scavenging material fine chemical plant (Tianjin, China). Dopamine hydrochloride (DA), tris(2,2′-bipyridine) dichlororuthenium(II)

hexahydrate,

tetrabutylammonium

hexafluorophosphate

(TBAPF6), acetonitrile (MeCN) and tetrahydrofuran (THF) were purchased from Sigma-Aldrich (USA). Analytical grade reagents and ultrapure water (18.2 MΩ.cm) were used. Apparatus. A MPI-E ECL detector (Xi'an Remax Electronics, China) and CHI 660D electrochemical workstation (Chenhua Instruments, China) were used for the ECL and electrochemical measurements. The ultraviolet-visible (UV-Vis) absorption and fluorescence spectra were recorded on an UV-2450 spectrophotometer (Shimadzu Corporation, Japan) and Cary Eclipse fluorescence spectrophotometer (USA), respectively. The fluorescence life time was measured on a Fluorolog-3 fluorescence spectrophotometer (Horiba JY, USA). The morphology of the nanoparticles was obtained from a Field Transmittance Electron Microscopy (TEM, Tecnai G2 F20, FEI, USA). Preparation of the DPA-CM NPs. As shown in Fig. 1A, the DPA-CM NPs were prepared by a reprecipitation method.17, 31 In brief, 1 mL of 10 µg/mL degassed 6


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DPA-CM in THF was quickly added to 3 mL water under sonication. The THF solvent was removed by rotary evaporation and aged in ice bath. Then the resulting NPs solution was filtered through a syringe filter (0.22 µm). ECL Measurements. 10 µL of 5 µg/mL DPA-CM NPs was dropped onto a glassy carbon electrode surface (GCE, 2 mm in diameter) and dried to obtain a DPA-CM NPs modified GCE (DPA-CM NPs/GCE). A conventional three-electrode system including a DPA-CM NPs modified working electrode, a platinum auxiliary electrode and an Ag/AgCl (saturated KCl) reference electrode was used. RESULTS AND DISCUSSION Characterization of the DPA-CM NPs. The DPA-CM NPs were prepared by a simple reprecipitation method using water as a poor solvent and THF as a good solvent. The resulting DPA-CM NPs were characterized by TEM, dynamic light scattering (DLS), UV-Vis and photoluminescence (PL) spectrum. Fig. 1B shows that the DPA-CM NPs have a spherical morphology and are mono-dispersed in a range of 3-8 nm with an average diameter of 5.82 nm. For the DLS measurement, the mean hydrodynamic radius is approximately 8.67 nm and the relative standard deviation in the particle size was 0.69 (for n = 5) for the DPA-CM NPs (Supporting Information Fig. S1). The slightly larger size in the DLS is ascribed to the solvent effect in the hydrated state and the light scattering.42 Preferred position for Figure 1. The resulting DPA-CM NPs in water were colorless and transparent (Fig. S2). The solution was stable for one month without obvious aggregation. The excellent stability is ascribed to the negative surface charge (the zeta potential of the DPA-CM NPs was measured to be -23.2 mV with a Malvern Nano-ZS90), in which the electrostatic

repulsion

in

the

nanoparticles

presumably

7


prevented

the


flocculation/coalescence of nanoparticles. Fig. 2A shows the UV-Vis spectra of the DPA-CM NPs and DPA-CM. Three absorption peaks at 243 nm, 300 nm and 335 nm were observed for the DPA-CM solution due to the π-π* transition. The UV-Vis absorption spectrum of the DPA-CM NPs in water shows an inconspicuous absorption peak at 275 nm (Fig. 2A, a). A red-shift (from 243 nm to 275 nm) was observed in the UV-vis spectrum of the DPA-CM NPs. The photoluminescence (PL) spectra of the DPA-CM NPs and DPA-CM did not mirror the absorption spectra. A broadened fluorescence emission with a maximum wavelength at 372 and 412 nm was observed for the DPA-CM NPs in water and DPA-CM in THF, respectively. An obvious blue-shift of 40 nm was observed for the DPA-CM NPs in water compared with DPA-CM in THF. The relative PL efficiency of DPA-CM in THF (λem,max = 412 nm when excited at 366 nm) was calculated to be 0.008 when the DPA was used as a standard in the same test condition (ΦPL = 0.95 in C2H5OH43). Surprisingly, the relative PL efficiency of the DPA-CM NPs (λem,max = 365 nm when excited at 310 nm) was increased to 0.06 in water. The low PL efficiency of DPA-CM may be ascribed to the intramolecular photoinduced electron transfer from the DPA moiety to the CM moiety 44 and the structural flexibility of DPA-CM.21 The lifetime was measured using a time-correlated single photon counting (TCSPC) technique,45,

46

and the PL dynamics of DPA-CM and the

DPA-CM NPs (using THF as a good solvent) were investigated at excited wavelength at 335 nm and at emission wavelengths of 412 nm and 372 nm, respectively. A bi-exponential decay function was used to fit the lifetime dynamics of DPA-CM while a mono-exponential decay function was used to fit the lifetime dynamics of the DPA-CM NPs (Supporting Information Fig. S3). The biexponential decay components (τ1 = 2.42 ns, amplitude = 72 %, τ2 = 9.27 ns, amplitude = 28 %) for 8


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DPA-CM in THF at 412 nm were associated with the monomer and excimer states of DPA-CM. The monoexponential decay (τ = 12.03 ns) was observed for the DPA-CM NPs at 372 nm in water (Table 1). Similar red-shifted absorption, blue-shifted emission and aggregation-induced enhanced PL emission characteristics were also observed for Spiro-BTA NPs,31 1-cyano-trans-1,2-bis-(4’-methylbiphenyl)-ethylene nanoparticles,

47

poly(p-phenyleneethynylene) film,

poly(p-phenyleneethynylene),

49

which

was

48

and cyclophane-decorated

attributed

to

the

restricted

conformational relaxation in NPs21 and J-aggregates formation.8 Preferred position for Figure 2. We also examine different good solvents, including THF and MeCN, on the photophysical behavior of DPA-CM NPs. It was found that the absorption and emission spectra of the DPA-CM NPs produced by their dispersion in THF was similar with that of DPA-CM NPs using MeCN as a good solvent, except that a 48 nm red-shift in the PL emission wavelength was observed at an excitation wavelength of 320 nm (Fig. S4). Additionally, excitation-dependent PL behavior was observed for the DPA-CM NPs in water using water as a poor solvent and THF or MeCN as good solvents (Fig. S5). The excitation-dependent PL behavior may result from the different sizes of the DPA-CM NPs in addition to the complexity of the excited states of the DPA-CM NPs.50 Electrochemiluminescence properties. The ECL properties of the DPA-CM NPs in aqueous solution along with DPA-CM in organic solution were investigated, respectively. Although no obvious oxidation wave was observed for DPA-CM NPs or DPA-CM NPs/GCE in 0.1 M phosphate buffer saline (PBS, 0.1 M Na2HPO4, 0.1 M NaH2PO4 and 0.1 M KCl, pH 7.40), a broad shoulder at ~ +1.3 V vs Ag/AgCl is observed (Fig. S6), which is different with the electrochemical behavior of DPA-CM 9



in the MeCN solvent (Fig. S7). Similar behaviors were found for semiconductor NPs.7, 51

Because of the limited potential window at more positive and more negative

potentials in aqueous solution, we tried to study the ECL using a coreactant process. Fig. 3A and 3B show cyclic voltammograms (CVs) and ECL intensity-potential profiles of the DPA-CM NPs modified GCE in the presence of TPA and S2O82-, respectively. One broad irreversible oxidation at +0.9 V vs Ag/AgCl on bare GCE is observed for the oxidation of TPA, which is similar with references.5,31 A catalytic current was observed on the DPA-CM NPs/GCE in 0.1 M PBS (pH 7.40) containing 50 mM TPA (Fig. 3A). One strong ECL emission at approximately +1.4 V was observed for the DPA-CM NPs/GCE in the presence of TPA (Fig. 3B, 9554 a.u.). The ECL emission came from DPA-CM NPs*, which generated from the reaction between radical TPA．(oxidation product of TPA) and DPA-CM NPs+ (oxidation product of DPA-CM NPs), following classic oxidative-reduction coreactant mechanism.5, 52 When using K2S2O8 as coreactant, one broad irreversible reduction at -1.2 V on GCE was observed for the reduction of K2S2O8 and a catalytic current was observed on the DPA-CM NPs/GCE (Fig. 3C).53 A small ECL emission (234 a.u.) was observed upon the reduction of DPA-CM NPs in the presence of K2S2O8, and it was ascribed to the reduction of both the S2O82- and the DPA-CM NPs. The ECL intensity of the DPA-CM NPs-K2S2O8 system (Fig. 3D) is smaller than that of TPA (Fig. 3B). The difference of the ECL intensities in the presence of TPA or K2S2O8 was also observed for 5 µg/mL DPA-CM NPs in the presence of 50 mM TPA or 50 mM K2S2O8 (Fig. S8). The difference of the ECL intensities in the presence of different coreactant was subsequently examined. CV of DPA-CM shows one reversible oxidation with E1/2 = +1.28 V and one irreversible reduction with Epc = -0.96 V, indicating good stability of the cationic radical. The oxidation of DPA-CM occurs on the DPA group, and the 10


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reduction occurs at the CM.44 For the ECL ion annihilation of DPA-CM in MeCN containing 0.1 M TBAPF6, a weak ECL signal (I = 112) in the positive potential scanning can be seen, and no obvious ECL signal in the negative potential scanning is present (Fig. S9 A, B). The coreactant ECL reaction of DPA-CM in the presence of TPA and BPO were also studied. A high relative ECL intensity (I = 1,286) was obtained for the oxidation of DPA-CM -TPA while no obvious ECL signal was observed for the reduction of DPA-CM-BPO (Fig. S9 C, D). Therefore, the different ECL intensities in the presence of different coreactant are ascribed to the different stabilities of the radical ion species. Preferred position for Figure 3. The DPA-CM NPs modified electrode exhibits outstanding reproducibility with a relative standard derivation (RSD) of 2.5 % (Fig. 4A). ECL spectrum of the DPA-CM NPs was obtained examined by using optical filters (300, 340, 360, 400 and 450 nm). Different wavelength filters (300, 340, 360, 400 and 450 nm) were placed in front of the transparent window of PMT and the corresponding ECL signals were recorded. The ECL spectrum was obtained by drawing a plot of wavelength vs ECL intensity. An ECL peak at approximately 365 nm was observed (Fig. 4B), which was close to the PL spectrum of the DPA-CM NPs (Fig. S10), indicating the ECL emission was generated from the excited DPA-CM NPs (Fig. 4C).54 Compared with the ECL intensity of DPA-CM, an aggregation-induced enhanced ECL emission was obtained for the DPA-CM NPs, and was attributed to the combined effects of the small size of DPA-CM NPs, the aggregation-induced enhanced PL emission and the good stability of the cationic radical of DPA-CM.8 Additionally, we found that DPA-CM NPs prepared using MeCN as a good solvent produced a much smaller ECL signal (i.e., injecting 1 mL of 10 µg/mL DPA-CM in MeCN into 3 mL water) (Fig. 11



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S11). This might be attributed to the lower solubility of DPA-CM in MeCN vs THF and the different miscibility of MeCN and THF with water.8,

55

The good stability

and relatively high ECL emission of the DPA-CM NPs/TPA system is promising in analytical applications. Preferred position for Figure 4. Analytical application for the detection of biomolecules. Considering the good ECL behavior of the DPA-CM NPs modified electrode, the ECL analytical application of the DPA-CM NPs modified electrode was illustrated for the detection of biomolecules. The detection of AA, UA and DA is very important in pharmaceutical analysis, the food industry and diagnostic applications.56 Therefore, ascorbic acid, uric acid and dopamine were used as model compounds to test the analytical application. It was found that the ECL emission of the DPA-CM NPs modified electrode was quenched by ascorbic acid, uric acid and dopamine. Therefore, the DPA-CM NPs modified electrode was employed for the determination of ascorbic acid, uric acid and dopamine in aqueous solution by the quenching phenomenon, providing a promising pathway in designing new methodologies for the detection of quencher and quencher-related analytes. It was found that the ECL intensity of the DPA-CM NPs/GCE in the presence of TPA decreased with the increases in concentration of ascorbic acid, uric acid and dopamine (Fig. 5). The ratio of the peak ECL intensity (I0/I) was used to quantify small molecules, where I0 is the ECL intensity of the DPA-CM NPs/GCE and I is that of the DPA-CM NPs/GCE in the presence of targets. The I0/I was directly proportional to the concentration of AA, UA and DA over the range from 0.05 µM to 50 µM. The linear regression equation was I0/I = 264870 C + 2.41 (the unit of C is M, r = 0.9924) for AA, I0/I = 48420 C + 1.60 (the unit of C is M, r = 0.9918) for UA and I0/I = 29820 C + 1.42 (the unit of C is M, r 12


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= 0.9828) for DA, respectively. The detection limit was 0.04 µM, 0.2 µM and 0.4 µM for AA, UA and DA (S/N = 3), respectively. RSD is 1.3 %, 1.0 % and 1.7 % for 5 µM AA, 5 µM UA and 5 µM DA with five repeat measurements (n = 5), respectively. The analytical performances for ascorbic acid, uric acid and dopamine are listed in Table S1, S2 and S3, indicating a reasonable sensitivity of the prepared DPA-CM NPs/GCE for the detection of AA, UA and DA. Although the electrodes cannot simultaneously detect AA, UA and DA, their selectivity can be improved in complex biological samples by using specific recognition materials (such as molecularly imprinted polymer57 or enzyme58) or through separation techniques.59 Additionally, the ECL intensity decreased nonlinearly with an increase in the target concentration while I0/I linearly increased with increase of target concentration. Therefore, a quenching constant can be calculated according to the Stern-Volmer equation (I0/I) - 1 = kCQ, in which CQ is the concentration of a quencher and k is the quenching constant.60 k, calculated by the linear regression of the plots, was 2.6×106, 4.8×105 and 2.9×105 M-1 for AA, UA and DA, respectively. The large value of k suggests a high sensitivity of the ECL method towards the detection of ascorbic acid, providing a promising way to detect ascorbic acid in complex samples. Preferred position for Figure 5. CONCLUSION Small organic nanoparticles of DPA-CM NPs with an average size of 5.82 nm were prepared using a reprecipitation method. Red-shifted absorption, blue-shifted PL emission and aggregation-induced enhanced ECL emission were observed for the DPA-CM NPs in aqueous solution compared with the original DPA-CM in organic solution, which may be attributed to the combined effects of the small DPA-CM NPs size, the restricted conformational relaxation in the NPs and the good stability of the 13



cationic radical of DPA-CM. The DPA-CM NPs in the presence of TPA exhibited strong and stable ECL emissions at a relatively high efficiency in aqueous solution. The ECL spectrum of the NPs generated with a coreactant in aqueous medium was similar with PL spectrum. Based on the ECL quenching, ascorbic acid, uric acid and dopamine were quantitatively determined in the range of 0.05 µM to 50 µM with high sensitivity. This is the first aggregation-induced enhanced ECL obtained from DPA-CM NPs and the first analytical application of DPA-CM NPs to monitor biomolecules. The donor-acceptor based organic NPs with aggregation-induced enhanced ECL emission and without a toxic heavy metal element as ECL emitter illustrates a method to generate functional nanomaterial and opens a novel analytical application to monitor biomolecules.

SUPPORTING INFORMATION The Supporting Information is available free of charge on the ACS Publications website The size distribution of the DPA-CM NPs, a picture of the DPA-CM NPs solution, the fluorescence lifetime, UV-Vis absorption and fluorescence spectra of the DPA-CM NPs prepared with MeCN as good solvent, Cyclic voltammogram, ECL intensity-potential profile, and analytical results for the detection of ascorbic acid, uric acid and dopamine. ACKNOWLEDGMENTS We thank the National Science Foundation of China (Nos. 21522504, 21375084 and 21475082), the 111 project (No. B14041) and the Fundamental Research Funds for the Central Universities (Nos. GK201603041 and 2016CBY001). REFERENCES 14


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and

Electrogenerated

Chemiluminescence

of

a

Spirobifluorene-Based Donor (triphenylamine)- Acceptor (2, 1, 3-benzothiadiazole) Molecule and Its Organic Nanoparticles. J. Am. Chem. Soc. 2011, 133, 5492-5499. (32) Zhao, Y.; Zhang, Q.; Chen, K.; Gao, H.; Qi, H.; Shi, X.; Han, Y.; Wei, J.; Zhang, C.

Triphenothiazinyl

Triazacoronenes:

Donor-Acceptor

17


Molecular

Graphene


Exhibiting

Multiple

Fluorescence

and

Electrogenerated

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(60) Stern, O.; Volmer, M. The Extinction Period of Fluorescence. Phys. Z. 1919, 20, 183-188. Figures, Table and Legends

Scheme 1. Molecular structure of DPA-CM (A), ascorbic acid (B), uric acid (C) and dopamine (D).

Figure 1. (A) Schematic diagram of the preparation of the DPA-CM NPs, (B) Typical TEM of the DPA-CM NPs, and (C) Size distribution of the DPA-CM NPs from TEM 21



image.

Figure 2. (A) UV−Vis absorption (a, b) and PL spectra (c, d) of the DPA-CM NPs in water (a, c) and DPA-CM in THF (b, d); PL spectra taken with excitation at 320 nm for DPA-CM NPs or 335 nm DPA-CM. (B) PL emission spectra of the DPA-CM NPs in water with progressively excitation wavelengths in the range of 320 nm to 440 nm with 20 nm increment.

Figure 3. CVs (A, C) and ECL intensity-potential profiles (B, D) at different

22


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electrodes in 0.1 M PBS (pH 7.40) containing 50 mM TPA (A, B) or 0.1 M PBS (pH 7.40) containing 50 mM K2S2O8 (C, D). Scan rate: 0.1 V/s. a, bare GCE, b, DPA-CM NPs modified GCE.

Figure 4. (A) ECL intensity-time curves of the DPA-CM NPs modified electrode. (B) ECL spectrum of the DPA-CM NPs modified electrode. Experimental conditions, 0.1 M PBS (pH 7.40) containing 50 mM TPA by pulsing the potential from 0 to 1.4 V vs Ag/AgCl. Pulse width is 0.3 s. (C) The ECL mechanism of the DPA-CM NPs.

23



Figure 5. (A) ECL intensity-potential profiles of the DPA-CM NPs modified GCE in 0.1 M PBS (pH 7.40) containing 50 mM TPA and different concentration of ascorbic acid. 0, 0.05, 0.1, 0.5, 1.0, 5.0, 10, 25, 50 µM (top to bottom). (B) ECL intensity-potential profiles of the DPA-CM NPs modified GCE in 0.1 M PBS (pH 7.40) containing 50 mM TPA and different concentration of uric acid. 0, 0.1, 0.5, 5.0, 25, 50 µM (top to bottom). (C) ECL intensity-potential profiles of the DPA-CM NPs modified GCE in 0.1 M PBS (pH 7.40) containing 50 mM TPA and different concentration of dopamine. 0, 0.1, 0.5, 5.0, 25, 50 µM (top to bottom). Scan rate, 0.1 V/s. (D) Relationship between I0/I and concentration.

24


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Table 1 Photophysical data for DPA-CM in organic solvent and DPA-CM NPs in water λem λabs (nm)

c

ε

ΦPL

τ (ns)

412

0.008

2.42, 72%; 9.27, 28%

(nm) a

b

243, 300,

3.8×104, 4.6 ×104, 5.1

335

×104 (M−1 cm−1)

275

2.09 ×104 (mL g−1cm−1)

372

0.06

12.03

275

8.2 ×103 (mL g−1cm−1)

420

0.01

9.39

DPA-CM

DPA-CM NPs (using

THF as good solvent) b

DPA-CM NPs (using MeCN as good solvent)

a

Measured in THF at a concentration of 1×10-5 M,

b

Measured in water at a

concentration of 5 µg/mL, c DPA as the standard (ΦPL = 0.95 in C2H5OH).

25



For TOC only

26


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Aggregation-Induced Enhanced Electrochemiluminescence from

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