Red Excimer Fluorescence from Dimeric

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C: Plasmonics; Optical, Magnetic, and Hybrid Materials

Highly-Efficient Orange-Red/Red Excimer Fluorescence from Dimeric #-# Stacking of Perylene and Its Nanoparticles Application Yue Shen, Zhe Zhang, Haichao Liu, Yan Yan, Shitong Zhang, Bing Yang, and Yuguang Ma J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.9b02447 • Publication Date (Web): 02 May 2019 Downloaded from http://pubs.acs.org on May 2, 2019

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The Journal of Physical Chemistry

Highly-Efficient Orange-red/Red Excimer Fluorescence from Dimeric π-π Stacking of Perylene and Its Nanoparticles Application Yue Shen,†,

⊥

Zhe Zhang,†,

⊥

Haichao Liu,†,

⊥

Yan Yan,‡ Shitong Zhang†, Bing Yang*, †and

Yuguang Ma§ †

State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin

University, Changchun, 130012, People’s Republic of China ‡

State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry,

Jilin University, Changchun, 130012, People’s Republic of China §

State Key Laboratory of Luminescent Materials and Devices, Institute of Polymer

Optoelectronic Materials and Devices, South China University of Technology, Guangzhou, 510640, People’s Republic of China

ABSTRACT: To achieve high-efficiency red excimer fluorescence, two novel perylene (PE) derivatives (mTPA-3PE and 2SF-3PE) are designed and synthesized with different monosubstituent triphenylamine (TPA) and spirofluorene (SF), respectively. The photophysical investigations reveal that mTPA-3PE and 2SF-3PE exhibit red/orange-red excimer fluorescence

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(637 nm and 610 nm) with long lifetimes (37.86 ns and 72.41 ns) in crystals, but significantly different photoluminescence (PL) efficiencies (24% and 77%). Both crystal structure and excited state property emphasize that the discreteness of PE dimer with π-π stacking is essentially responsible for the high-efficiency excimer emission in crystal. Using PE as π-π emissive core in this work, highly-efficient red excimer fluorescence is harvested in crystal for the first time. Moreover their nanoparticles with same excimer fluorescence exhibit the advantage of easyprocessing and the promising application in cell-imaging. Once again, our results validate the mechanism of excimer-induced enhanced emission (EIEE) by the discrete dimeric π-π stacking of PE in solid state, which opens a new way to develop high-efficiency narrow bandgap (e.g., Near-Infrared) light-emitting materials using EIEE mechanism in the future.

1. INTRODUCTION High-efficiency organic red light-emitting materials are always highly desired owing to the important applications in many fields, such as flat-panel displays, solid-state lighting, photodynamic therapy, organic solar cells and chemo-sensing, etc.1-8 Generally, the achievement of red fluorescent materials mainly depends on two approaches: covalent molecular synthesis and noncovalent intermolecular aggregation.3,

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As is known to all, the modification and

tailoring of organic structures endow the diversity of molecular designs for single-molecule red fluorescent materials, such as extending π-conjugation of aromatic systems, and selecting strong donor–acceptor (D-A) framework to decrease the emission bandgap between highest occupied molecular orbital (HOMO) of donor and lowest unoccupied molecular orbital (LUMO) of acceptor.3,9 Beyond that, the intermolecular aggregation actually induces the orbital energy level


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splitting and bandgap narrowing, and sometimes this is a more favorable way to realize red emission relative to the single molecule (which may be subject to complicated synthetic routes and rigorous reaction conditions) by the strong supramolecular interactions in solid states, such as π-π stacking, hydrogen and halogen-bonding, etc.10-13 However, one of the biggest challenges to achieve high-performance red fluorescent materials is still the sharp conflict between high efficiency and narrow bandgap according to the energy gap law.14 As a matter of fact, solid-state fluorescence of aromatic molecules is often encountered with the aggregation-caused quenching (ACQ), which can be ascribed to the formation of low-lying and non-emissive “dark” excited state species upon the aggregations through the strong π-π interactions, such as excimer.15-18 Previously, this kind of stacking form is strictly prevented by bulky-substitution and host-guest doping in many organic aromatic systems for the efficient monomer fluorescence.19-21 As we know, excimer (i.e., excited dimer) is a typical bimolecular excited species, which is the smallest and simplest model to better understand the structure-property relationship of supramolecular luminous aggregates.22-26 To be different from the previous excimer quenching fluorescence, the strong excimer emission (their PL efficiencies are around 80%) of several anthracene (AN) derivatives in solids have been reported recently, which are all featured with a discrete pairwise π-π stacking of AN units in crystals.27-31 Green excimer fluorescence was commonly obtained from AN π-π stacking, but the red excimer materials are still rare so far.32-39 For the further red-shifted excimer emission, our strategy is to enlarge the π-conjugation degree (the number of fused rings) of π-moiety monomer, aiming at decreasing the energy of excimer emissive state by two contributions: the enhanced π-π interaction between two π-moieties, as well as the stabilized monomeric locally-excited (LE) state. In the meantime, this enhanced π-π interaction will preferentially induce the molecular aggregation in a π-π stacking mode between


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two monomers, which surely facilitates the formation of dimeric π-π stacking in solid states, especially in the more practical amorphous films or nanoparticles. Perylene (PE) is an aromatic molecule with a larger π-conjugation plane than naphthalene (NA) and AN, whose derivatives have been widely applied in the biological probes and sensors due to the excellent optical and electronic properties.40-42 AN as linear molecule can not form excimer even in high-concentration solution and packs in a sort of herringbone mode in solid state, but some modifications of AN unit can achieve the formation of AN excimer.43-44 In sharp contrast, PE as planar molecule can form sandwich types dimers, which after excitation can relax to an excimer, both in both solution and solid state.45-47 The reason is that PE has the larger πconjugation and stronger π-π interaction than AN. Compared with the AN, PE shows not only the more red-shifted emissions in monomers, but also the more likely π-π stacking to form excimer in solid state. So it is the most favorable π-moiety to achieve the high-efficiency red excimer fluorescence by using the same strategy of discrete dimeric π-π stacking in solid state, as mentioned in our previous works.27-28, 48 On the one hand, the universality of this strategy will be further verified to better understand the excimer-induced enhanced emission (EIEE) mechanism according to the various excimer species with different emission colors. On the other hand, the discrete dimeric π-π stacking of PE is expected to be formed more easily in amorphous film or nanoparticle for the development of practical applications than those of AN, as a result of the greatly enhanced π-π interaction between two perylenes. Herein, we designed and synthesized two PE derivatives. Firstly, triphenylamine (TPA) was chosen to produce a new compound 3-(perylen-3-yl)-N, N-diphenylaniline (mTPA-3PE). As a result, mTPA-3PE was found to display the largely red-shifted emission (λmax = 637 nm) in crystal relative to that in its monodisperse film (λmax = 496 nm), which can be ascribed to the PE


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excimer emission from antiparallel dimeric PE π-π stacking. Consequently, its PL efficiency is 24% due to the contact interactions between luminophors - PE dimers. To imporve PL efficiency, a larger side group spirofluorene (SF) was introduced to obtain the other compound 2-(perylen3-yl)-9,9'-spirobi[fluorene] (2SF-3PE). Not only is high-efficiency orange-red PE excimer emission (77%) observed in crystal, but also this excimer fluorescence can be harvested in nanoparticles, which further enables the cell-imaging application with the excellent dyeing effect. This work suggests that EIEE mechanism is an effective and practical way to achieve highefficiency and narrow-bangap light-emitting materials. 2. EXPERIMENTAL SECTION The details of synthesis and structure characterization can be found in the Supporting Information. All the reagents and solvents used for organic synthesis were purchased from Sigma-Aldrich and Acros companies and used without further purification. The amphiphilic functional polymer poly(styrene-co-maleic anhydride) (PSMA, cumene-terminated, average MW~1,700, styrene content = 68%) and solvent tetrahydrofuran (THF, anhydrous, 99.9%) were purchased from Sigma-Aldrich (Shanghai, China). CCDC 1893816, 1893817 contains the supplementary crystallographic data for 2SF- 3PE, mTPA-3PE. UV-vis spectra were recorded using Shimadzu UV-3100 Spectrophotometer. Steady-state fluorescence spectra and fluorescence lifetimes were carried out with FLS980 Spectrometer. Single crystal diffraction measurements were performed on a Bruker APEXII CCD system. The crystal structures were solved with direct methods and refined with a full-matrix least-squares technique using the SHELXS programs. All angles and distances in crystals were measured using Mecury 1.4.1 Software. The particle sizes of nanoparticles in bulk solution were


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characterized by dynamic light scattering (Malvern Zetasizer NanoS). TEM measurements were recorded on a JEOL JEM-2100F using ultra-thin carbon films as grids. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were used to describe the ground-state and excited-state properties. For all the calculations in single molecule, optimized ground and excited state geometries were obtained at the levels of M06-2X /6-31G (d, p). For all the dimers, optimized excited state geometries were obtained by using the M06-2X hybrid functional at 6-31G (d, p) level. The Natural transition orbitals (NTOs) were evaluated with the dominant “particle”-“hole” pair contributions and the associated transition weights. All the calculations were carried out using Gaussian-09 package on a Power Leader cluster. Furthermore, the Multiwfn software was used to calculate the wave function of electron-hole pair from the transition density matrix by TD-DFT, and was plotted in a two-dimension (2D) color-filled map for easily distinguishing the dimer ground and excited state character. 3. RESULT AND DISCUSSION 3.1. Molecular design. For high-efficiency red excimer fluorescence, two key points should be of particular concern in molecular design: red excimer emission core and its discrete dimeric π-π stacking. To construct red-shifted excimer emission core, our strategy is to gradually enlarge the π-conjugation degree of π-monomer, for the purpose of the decreased energy of excimer emissive state, as shown in Figure 1a. Larger π-conjugation plane means the narrower HOMOLUMO gap for monomer and stronger π-π interaction between two π-monomers can further induce the wider energy splitting between monomeric HOMO-HOMO and LUMO-LUMO for dimer. Consequently, with the increasing number of fused rings from NA, AN to PE, both the narrowed HOMO-LUMO gap of monomer and the broadened energy splitting of dimer jointly


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Figure 1. (a) Schematic diagram of electronic structures for red-shifted excimer emission (NA: ground-state of naphthalene; NA*: excited-state of naphthalene; (NANA)*: excimer state of naphthalene; AN: ground-state of anthracene; AN*: excited-state of anthracene; (ANAN)*: excimer state of anthracene; PE: ground-state of perylenes; PE*: excited-state of perylene; (PEPE)*: excimer state of perylene). (b) Molecule design of discrete dimeric π-π stacking. give rise to the significantly red-shifted emission of excimer according to a single one-electron excitation from HOMO to LUMO.49 From previous reports, the excimer emission of PE is right in the region of red-light, while the excimers of NA and AN show ultraviolet and green emissions, respectively.45-46, 49-52 As a result, PE dimer with cofacial π-π stacking is confidently chosen as the red excimer emission core.


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Furthermore, for the high-efficiency red fluorescence of PE excimer, the discrete dimeric π-π stacking should be arranged for PE, according to a series of highly efficient AN excimers that have been reported in our group.27-31 To realize the discrete dimeric π-π stacking of PE, the target candidate is designed into one-substituent PE, as shown in Figure 1b. That is to say, PE derivatives should consist of two moieties: a planar aromatic PE (π-moiety) and a one-sided substituent (side-moiety). First, the one-sided substitution is still favorable enough for PE πmoiety to form anti-parallel dimeric cofacial π-π stacking with appropriate steric hindrance. Next, the one-sided substituent can serve as the spacer to separate PE dimer from each other using its proper size and suitable orientation, aiming at the discrete dimeric π-π stacking of PE moiety in solid state. Notably, the size and orientation of one-side substituent play very important role in the construction of spatially-isolated dimeric π-π stacking of PE moieties for the purpose of the enhanced PE excimer emission. In this contribution, two PE derivatives (mTPA-3PE and 2SF3PE) with one-sided substituents (TPA and SF) were designed and synthesized by Suzuki coupling reaction (see Supporting Information and Scheme S1). And then, they were further investigated about the photophysical properties, together with the crystal packing structures, excited-state properties and nanoparticle application in cell-imaging. 3.2. Photophysical properties of mTPA-3PE. Firstly, both absorption and emission of mTPA-3PE were measured in different solvents, corresponding to the photophysical properties of ground state and excited state, respectively. For UV-vis absorption spectra in Figure 2a, three main absorption bands can be assigned to the characteristic absorption of TPA (300 nm) and PE (250 nm, 350-475 nm with vibrational fine structure) (Figure S1), respectively. 45 With the increasing solvent polarity, absorption spectra show the almost negligible changes. But for the PL spectra (Figure 2b), there is a new peak around 620 nm in high polar solvent such as


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Figure 2. (a) UV–vis absorption spectra of mTPA-3PE with increasing solvent polarity. (b) Fluorescence spectra of mTPA-3PE with increasing solvent polarity; inset is the chemical structure of mTPA-3PE. (c) Fluorescence spectra of mTPA-3PE in different solid states; photos of mTPA-3PE in different solid states under the illumination of a 365 nm UV lamp. (d) Transient PL decay measurements of mTPA-3PE in different solid states. acetonitrile, which is attributed to ICT state (Figure S2-S3) Besides, we observe that absorption and emission spectra exhibit good mirror symmetry, as a result of the planarity and rigidity of PE unit as an emissive core, as shown in Figure 2a and 2b. Furthermore, the photophysical properties of mTPA-3PE were carefully characterized in solid states (Figure 2c and 2d). For the


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1 wt% doped film in polymethyl methacrylate (PMMA), mTPA-3PE exhibits the very bright bluish-green emission with main peak at 496 nm. Although the obvious structured PL spectra remain, the 0-1 vibration dominates PL intensity in film while 0-0 vibration dominates PL intensity in solutions, probably arising from the formation of weakly coupled aggregate in film rather than in solutions.53 The transient PL spectra reveal the averaged lifetime is 12 ns in monodisperse film.54 In the meantime, the crystal of mTPA-3PE was grown through a slow solvent evaporation and diffusion process in tetrahydrofuran (THF). Interestingly, the crystal exhibits the significantly distinct photophysical properties relative to those of doped film and solution. Not only is the largely red-shifted emission (637 nm) observed together with disappeared vibrational fine structure and obviously broadened full width at half maximum (FWHM = 135 nm), but also mTPA-3PE crystal shows a mono-exponential decay of transient PL spectrum with a single lifetime as long as 37.86 ns, which is much longer than those in doped film and solution. Compared with the single molecule, the emission behaviors (large red shift, broadening and long lifetime) of crystal are in very good agreement with the spectral characteristics of PE excimer.45,47,55 Subsequently, PL efficiency of mTPA-3PE was evaluated by integrating-sphere experiment to be 97% and 24% for doped film and crystal, respectively. From monomer to dimer, the PL efficiency of mTPA-3PE shows obvious ACQ, which appears to conform the conventional view that excimer is usually low-efficiency. Though the PL efficiency of mTPA-3PE crystal is not as high as those of AN excimer we have reported previously, it is much better than some classic red dyes, such as 4-(dicyanomethylene)-2-methyl-6-(4dimethylaminostyryl)-4H-pyran (DCM), rubrene and Nile red, etc.32 Besides, for the future practical application, the neat thin film of mTPA-3PE was also prepared by vacuum evaporation, and its emission is peaked at about 600 nm (Figure S4a). Although the emission of neat film is


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some blue-shifted relative to that of crystal, the transient PL spectrum confirms that there is long lifetime component (Figure S4b), indicating the formation of PE excimer to a certain degree. If the operating conditions were further optimized during vacuum evaporation process, the fluorescence properties of neat film could be expected to be completely consistent with crystal, which makes the excimer film possible to be applicable to organic light-emitting diodes and organic field-effect light-emitting transistors in the near future. 3.3. Photophysical properties of 2SF-3PE. To promote PL efficiency of PE excimer, mTPA substituent is replaced with SF unit, and then we designed and synthesized the other PE derivative (2SF-3PE). Like those in mTPA-3PE, the photophysical properties of 2SF-3PE were carefully characterized in solution, film and crystal (it was prepared by sublimation), respectively. In different solvents (Figure S5 and S6), 2SF-3PE shows very similar absorption spectra compared to those of mTPA-3PE, except for the structured absorption band at 300 nm from SF moiety. As for the PL spectra, no ICT characteristic can be observed even in high polar solvent. For 1wt% doped film in PMMA (Figure 3a and 3b), 2SF-3PE demonstrates a slightly red-shifted maximum emission wavelength at 509 nm relative to 496 nm of mTPA-3PE, which is ascribed to the smaller twisting angle between PE and its substituent group in the excited state (Figure S12 and S17). The lifetimes at different emission wavelength (476 nm and 509 nm) were measured, and the average lifetimes were estimated to be 8.24 ns and 11.00 ns, respectively. More interestingly, the crystal of 2SF-3PE exhibits a very intense orange-red fluorescence with an emission maximum wavelength at 610 nm (Figure 3c), which is somewhat blue-shifted in contrast to 637 nm of mTPA-3PE crystal, but red-shifted in contrast to 578 nm of α-phase PE dimer crystal.45, 47 It is noteworthy that the PL efficiency of 2SF-3PE crystal was measured to be 77% as we expected in molecular design, which is much higher than that of mTPA-3PE (ηPL =


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Figure 3. (a) Fluorescence spectrum of 2SF-3PE of 1 wt% film in PMMA. (b) Transient PL decay measurement of 2SF-3PE of 1 wt% film in PMMA. (c) Fluorescence spectrum of 2SF3PE crystal. (d) Transient PL decay measurement of 2SF-3PE crystal; inset is the chemical structure of 2SF-3PE. 24%) and α-phase PE dimer (ηPL = 36%) crystals. Furthermore, the transient PL spectrum (Figure 3d) revealed a mono-exponential decay with a lifetime as long as 72.41 ns. In addition, the other 2SF-3PE crystal was obtained through a slow evaporation and diffusion of solvent THF, which is named as crystal-G because of the green fluorescence emission (λmax = 528, 557 nm) under UV irradiation (Figure S8). The average lifetime was calculated to be 3.90 ns at λmax = 528 nm by transient PL spectrum. According to both fluorescence emission and lifetime, it can


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be speculated that the crystal-G showed the monomer-like fluorescence properties, which are also similar to those of single molecule in all solutions. However, compared with the redemitting crystal, the PL efficiency of crystal-G is obviously decreased to be only 14% probably due to fluorescence quenching from the intermolecular interaction between PE units. Therefore, 2SF-3PE crystal not only successfully achieved the high-efficiency red PE excimer fluorescence for the first time, but also confirmed the EIEE mechanism once again. 3.4. Nondiscrete and discrete dimeric stacking. In order to better understand the difference in photophysical properties of these two compounds, especially for the distinct PL efficiency in two crystals, the crystal structures of mTPA-3PE and 2SF-3PE were determined by single-crystal X-ray diffraction experiment, respectively. Their crystal structures are shown in Figure 4 for the purpose of comparison, and the detailed crystal data are listed in supporting information (Table S1-S2). Similarly, both mTPA-3PE and 2SF-3PE crystals belong to monoclinic crystal system and centrosymmetric space groups of P2 1 /c. As expected by molecular design, both crystal structures show the anti-parallel dimeric π-π stacking of PE moieties with the nearly same overlap ratio of 60% between two PE planes (top view). And also, the dimeric π-π stacking is all formed through two different kinds of conformations of single molecule, which are exactly in Ci symmetry for this dimer. To be different, for the single molecule, the twisting angle of mTPA3PE between PE and its substituent group is 54.20°, which is smaller than 69.31° of 2SF-3PE. For the dimeric π-π stacking of PE, the interplanar distance between two PE moieties is about 3.601 Å in 2SF-3PE crystal (side view), which is obviously larger than 3.456 Å of mTPA-3PE crystal within a typical π-π interaction distance. For the reason, it can be mainly ascribed to the fact that there is a larger twisting angle between the PE unit and substituent in 2SF-3PE crystal, and the nearly vertical benzene ring structure prevent the PE unit close to each other. Most


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Figure 4. Single-crystal structures of (a) mTPA-3PE and (b) 2SF-3PE. importantly, the PE dimer stacking is totally different in mTPA-3PE and 2SF-3PE crystals. Specifically, the PE dimer in 2SF-3PE crystal is well isolated by peripheral four SF moieties through multiple C-H•••π interaction between PE moieties and fluorene moieties (Figure S10b), i.e., discrete PE dimer stacking. Whereas in mTPA-3PE crystal, the PE dimer is surrounded by the other four PE dimers through multiple C-H•••π interaction between PE and PE moieties (Figure S10a), i.e., nondiscrete PE dimer stacking. Obviously, the structure-property relationship can be better understood for the distinct dimer emission in two crystals of mTPA-3PE and 2SF-


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3PE. Namely, the discrete dimeric π-π stacking of PE is mainly responsible for high-efficiency excimer fluorescence in 2SF-3PE, while the nondiscrete dimeric stacking results in a relatively low efficiency of excimer emission in mTPA-3PE crystal, which is essentially related to the intensified nonradiations triggered by the exciton delocalization and diffusion due to the interactions between PE dimers (Table S3). At this point, α-phase crystal of PE further confirms that the nondiscrete dimeric π-π stacking causes low PL efficiency (ηPL = 36%) of excimer fluorescence, which has almost the same crystal packing of PE dimer as that in mTPA-3PE crystal (Figure S11). Thus, the discrete dimeric π-π stacking is substantially verified to be important for high-efficiency excimer fluorescence, as a result of the enhanced localization of emissive exciton. 3.5. Excimer excited state properties. Moreover, the excited-state properties were evaluated to gain a deep insight into the intrinsic photophysics of these π-π dimeric structures in crystal. Firstly, the lowest excited states (S1) geometries were obtained by geometry optimization at the level of time-dependent density functional theory (TDDFT, M06-2X/6-31G) using monomer and dimer in mTPA-3PE and 2SF-3PE crystals as initial geometry, respectively.30 For the monomers at excited state, both mTPA-3PE and 2SF-3PE show the more planar PE moiety and the reduced twist angle between PE and TPA/SF relative to the ground state in vacuum conditions/crystals, indicating the enhanced π-conjugation along the molecular backbone (Figure S12 and S17). For the dimers at excited state, the π-π interplanar distances between two PE moieties are obviously shortened by 0.155 Å and 0.331 Å relative to those in initial crystals of mTPA-3PE and 2SF-3PE respectively, together with the enlarged overlap ratio between two PE moieties from 60% to 88%/84% (Figure S16 and S21). Compared with the dimer structures in both crystals, the optimized geometries of excited state tend to be an almost fully cofacial π-π stacking with a


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Figure 5. (a) NTOs from S1 to S0 of mTPA-3PE (left) dimer and 2SF-3PE (right) dimer from respective optimized geometries. (b) Transition density matrix (TDM) color-filled maps of the S1 state of mTPA-3PE (left) dimer and 2SF-3PE (right) dimer. “compressed” π-π interplanar distance, revealing a great enhancement in the rigidity of excimer geometry. By the way, the emission energies were estimated based on the optimized geometry of excited state, which is in very good agreement with experimental results (Figure 5). Secondly, both natural transition orbital (NTO) and electron-hole pair wavefunction were used to describe the excited state character and transition composition. For the monomers of mTPA-3PE and 2SF3PE, both “hole” and “eletron” are mainly localized on PE moiety for S1 →S0 transition


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(Figure S12 and S17), which is very well consistent with the LE state emission of PE in solution and doped film. For their dimers, the emission NTOs (S1 → S0) obviously show the stronger interaction between two monomers of PE than those of absorption (S0→S1) (Figure S13 and S18), as a result of the almost completely overlapping and “compressed” π-π distance between two PE planes. At the dimer excited state, “hole” is obtained from negative linear combination between two HOMO orbitals of monomers, while “eletron” is corresponded to the positive linear combination of two LUMO orbitals of monomers. Only based on the NTOs, the excited state character and quantitative transition composition cannot be further analyzed due to a completely symmetrical distribution of wavefunctions. Finally, the wavefunction of electron-hole pair was plotted into a two-dimensional color-filled map to disclose the nature of excited state according to transition density matrix using Multiwfn software.56-57 For the 2D color-filled map, both the horizontal axis xi and the vertical axis yi run over all the non-hydrogen atoms of dimer, as labeled in Figure S14 and S19. The brightness of each coordinate point (xi, yi) is directly proportional to the probability of |c(xi, yi)|2 of finding both electron and hole. At the dimer geometry of ground state from crystal, the brightest zone is localized primarily along the diagonal of 2D color-filled map (Figure S15 and 20), which indicates that both electron and hole are localized on a single PE unit, and thus the electronic transition has a dominant LE character. In a different way, the brightest zone are distributed along both diagonal and off-diagonal as shown in Figure 5, corresponding to two kinds of electronic transitions with LE character and intermolecular charge-transfer (CT) character, respectively. Both LE and CT transition characters coexist in one excited state, which can also be regarded as a hybridized local and charge-transfer (HLCT) excited state.4,58-67 As a comparison, both mTPA-3PE and 2SF-3PE have very similar HLCT character and composition of excited state, so the excited state property is


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impossible to be key factor responsible for the significant difference of excimer fluorescence between mTPA-3PE and 2SF-3PE. Therefore, the high-efficient excimer fluorescence of 2SF3PE crystal can be attributed to two main reasons: HLCT-featured state induces “compressed” excimer geometry for the effective suppression of nonradiative vibrational quenching, as well as the discrete dimeric π-π stacking guarantees the purity and singleness of excimer state as a result of excition localizatio, preventing the occurrence of “dark” state from nonradiative energy transfer. In a word, the discreteness of π-π stacking PE dimer is of great importance to achieve high-efficiency excimer fluorescence in solid state. 3.6. Nanoparticle cell-imaging application. To develop the practical applications of excimer materials, the primary requirement is that the discrete dimeric π-π stacking of PE should be easily formed in non-crystalline (amorphous) solids, such as film and nanoparticle, etc. At least, the dimeric π-π stacking should be formed with a sufficient proportion to satisfy the complete energy transfer from monomer to excimer. As mentioned above, the excimer emissions have been clearly observed in the vacuum-evaporated film for both mTPA-3PE and 2SF-3PE, but the film-forming conditions need to be further carefully optimized. Here, mTPA-3PE was attempted to make into nanoparticles to investigate its properties. The nanoparticles were prepared by the reprecipitation method, in which the emitter molecule was encapsulated by poly (styrene maleic anhydride) (PSMA), because of hydrophilic and hydrophobic interactions resulting in stable aqueous solutions. With the increase of doping concentration (mTPA-3PE:PSMA), absorption bands around 390 nm gradually appear and increase in contrast with those in dilute solutions (Figure S22), which is assigned to H-aggregation of PE unit. For the PL spectra, when the doping concentration is lower than 10%, only monomeric fluorescence can be observed. The excimer fluorescence gradually arises, as the doping concentration is more than 20%. Once the


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Figure 6. Characterizations of 2SF-3PE nanoparticles and specific cell labelings. (a) Hydrodynamic diameter of the nanoparticles. The inset shows a representative TEM image. The scale bar represents 50 nm; (b) Spectral character of the nanoparticles at the ratio at 80%; (c) and (d) are confocal images of Hela cell after incubation them with nanoparticles. doping proportion reaches 60%, the excimer fluorescence peaked at 632 nm dominates the whole PL spectra, together with the entirely disappeared monomer emission, indicating the pure excimer emission from π-π stacking PE dimer. For the transient fluorescence decay spectra, the lifetimes are very short (< 10 ns) when the doping concentrations are less than 30%. Once the doping concentration reaches 40%, the lifetimes are significantly increased to be tens of nanoseconds. With the further increase of doping concentration (80%), the lifetime is extended


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longer with the mono-exponential decay character, which is well consistent with that of mTPA3PE crystal (Figure S23 and Table S4). However, the PL efficiency of nanoparticles is still low, for example, it is less than 1% when doping concentration is 80%, probably due to the weakened rigidity of surrounding in nanoparticles. Subsequently, we successfully fabricated the 2SF-3PE nanoparticles, with the doping concentration of 80%, which exhibit spherical morphology with an average diameter at about 30 nm as characterized by dynamic light scattering (DLS), and transmission electron microscopy (TEM), as is shown in Figure 6a. The absorption spectrum (Figure 6b) is similar to that in solution, but the peak intensity at 400 nm is obviously higher than 460 nm, which is also attributed to H-aggregation of PE section.68 For the PL spectra, it shows the same peak position and spectral profile compared with its crystal. Notably, the PL efficiency is about 9%, higher than mTPA-3PE nanoparticles and other imaging materials.69-70 Next, these nanoparticles were explored for application in the bio-imaging of Hela cells. After Hela cells were incubated followed by incubation with these nanoparticles, the fluorescence signal can be clearly observed in Hela cell from the imaging as shown in Figure 6c and 6d, indicating an excellent dyeing effect. From further detailed observation, a large amount of fluorescence signals appear in cytoplasm, but are very weak in cell nucleus. This phenomenon confirms that the nanoparticle can successfully enter into cell without external force, exhibiting good cell permeability. After dyeing, cell did not change structure from morphological feature, implying cell still survive healthily. Taken together, the above results make the material a promising probe for cell fluorescence imaging. 4. CONCLUSION


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In summary, we designed and synthesized two novel PE derivatives (mTPA-3PE and 2SF3PE) with one-sided substituents of TPA and SF, respectively. Compared with the single molecule emission in dilute solution, the fluorescence of two crystals exhibits a large red-shift (637 nm of mTPA-3PE and 610 nm of 2SF-3PE), a long lifetime (37.86 ns of mTPA-3PE and 72.41 ns of 2SF-3PE) and a high efficiency (24% of mTPA-3PE and 77% of 2SF-3PE). Single crystal X-ray diffraction experiments reveal that discrete anti-parallel dimeric π-π stacking of PE moieties in 2SF-3PE crystal induces a higher efficiency than that of nondiscrete PE dimers in mTPA-3PE crystal. Once again, these results validate the mechanism of EIEE in the PE dimer system using the strategy of discrete dimeric π-π stacking in solid state, which is essentially ascribed to the increased rigidity of excited-state geometry due to HLCT characteristic of excimer excited state and the effective suppression of nonradiative energy transfer into “dark” state owing to the enhanced localization of emissive exciton. Using PE as π-moiety of monomer, not only was the highly-efficient orange-red/red excimer fluorescence achieved in crystal for the first time, but also the highly-efficient excimer fluorescence can be realized in nanoparticle with simple processing. As a practical application, the nanoparticle was applied to Hela cell-imaging, which shows the very promising probe in biological assays. In a word, this work provides us a new avenue to develop high-efficiency narrow bandgap light-emitting materials using the mechanism of EIEE.

ASSOCIATED CONTENT Supporting Information The following files are available free of charge on the ACS Publications website.


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General information on characterization and measurements, synthesis routes, photophysical properties, crystal structures and theoretical calculation details: S-I, Characterization and Measurements; S-II, Synthesis and Preparation; S-III, Figures and Tables; S-IV, References (PDF) 2SF-3PE crystal file (cif) 2SF-3PE crystal ckeckcif file (PDF) mTPA-3PE crystal file (cif) mTPA-3PE crystal crystal ckeckcif file (PDF) AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] Author Contributions Y. Shen., Z. Zhang. and H. Liu. contributed equally to this work.

⊥

Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by the National Basic Research Program of China (2015CB655003, 2016YFB0401001), the National Natural Science Foundation of China (51673083, 51873077 and 51473063), the Postdoctoral Innovation Talent Support Project (BX201700097 and BX20180121), the China Postdoctoral Science Foundation (2017M620108 and 2018M641767)


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and the Open Project Foundation of the State Key Laboratory of Luminescence and Applications (Changchun Institute of Optics, Fine Mechanics and Physics of the Chinese Academy of Science, SKLA-2016-04). ABBREVIATIONS Perylene, PE; triphenylamine, TPA; spirofluorene, SF; photoluminescence, PL; excimer-induced enhanced emission, EIEE; donor–acceptor, D-A; highest occupied molecular orbital, HOMO; lowest unoccupied molecular orbital, LUMO; aggregation-caused quenching, ACQ; anthracene, AN; locally-excited, LE; naphthalene, NA; 3-(perylen-3-yl)-N, N-diphenylaniline, mTPA-3PE; 2-(perylen-3-yl)-9,9'-spirobi[fluorene], 2SF-3PE; intramolecular charge-transfer, ICT; polymethyl methacrylate, PMMA; tetrahydrofuran, THF; full width at half maximum, FWHM; 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran, DCM; time-dependent density functional theory, TDDFT; natural transition orbital, NTO; charge-transfer, CT; hybridized local and charge-transfer, HLCT; poly (styrene maleic anhydride), PSMA; dynamic light scattering, DLS;, and transmission electron microscopy, TEM REFERENCES (1)

Qin, W.; Ding, D.; Liu, J.; Yuan, W. Z.; Hu, Y.; Liu, B.; Tang, B. Z. Biocompatible

Nanoparticles with Aggregation-Induced Emission Characteristics as Far-Red/Near-Infrared Fluorescent Bioprobes for In Vitro and In Vivo Imaging Applications. Adv. Funct. Mater. 2012, 22, 771-779. (2)

Huang, J.; Liu, Q.; Zou, J. H.; Zhu, X. H.; Li, A. Y.; Li, J. W.; Wu, S.; Peng, J.; Cao, Y.;

Xia, R., et al. Electroluminescence and Laser Emission of Soluble Pure Red Fluorescent Molecular Glasses Based on Dithienylbenzothiadiazole. Adv. Funct. Mater. 2009, 19, 29782986.


23


(3)

Page 24 of 34

Liu, T.; Zhu, L.; Zhong, C.; Xie, G.; Gong, S.; Fang, J.; Ma, D.; Yang, C.

Naphthothiadiazole-Based Near-Infrared Emitter with a Photoluminescence Quantum Yield of 60% in Neat Film and External Quantum Efficiencies of up to 3.9% in Nondoped OLEDs. Adv. Funct. Mater. 2017, 27, 1606384-1606390. (4)

Yao, L.; Zhang, S.; Wang, R.; Li, W.; Shen, F.; Yang, B.; Ma, Y. Highly Efficient Near-

Infrared Organic Light-Emitting Diode Based on a Butterfly-Shaped Donor-Acceptor Chromophore with Strong Solid-State Fluorescence and a Large Proportion of Radiative Excitons. Angew. Chem. Int. Edit. 2014, 53, 2119-2123. (5)

Ge, J.; Lan, M.; Zhou, B.; Liu, W.; Guo, L.; Wang, H.; Jia, Q.; Niu, G.; Huang, X.; Zhou,

H., et al. A Graphene Quantum Dot Photodynamic Therapy Agent with High Singlet Oxygen Generation. Nat. Commun. 2014, 5. (6)

Mathew, S.; Yella, A.; Gao, P.; Humphry-Baker, R.; Curchod, B. F. E.; Ashari-Astani,

N.; Tavernelli, I.; Rothlisberger, U.; Nazeeruddin, M. K.; Graetzel, M. Dye-Sensitized Solar Cells with 13% Efficiency Achieved through the Molecular Engineering of Porphyrin Sensitizers. Nat. Chem. 2014, 6, 242-247. (7)

Wu, C.; Chiu, D. T. Highly Fluorescent Semiconducting Polymer Dots for Biology and

Medicine. Angew. Chem. Int. Edit. 2013, 52, 3086-109. (8)

Niu, Y. H.; Tung, Y. L.; Chi, Y.; Shu, C. F.; Kim, J. H.; Chen, B. Q.; Luo, J. D.; Carty,

A. J.; Jen, A. K. Y. Highly Efficient Electrophosphorescent Devices with Saturated Red Emission from a Neutral Osmium Complex. Chem. Mater. 2005, 17, 3532-3536.


24

Page 25 of 34 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


(9)

Lu, H.; Zheng, Y.; Zhao, X.; Wang, L.; Ma, S.; Han, X.; Xu, B.; Tian, W.; Gao, H.

Highly Efficient Far Red/Near-Infrared Solid Fluorophores: Aggregation-Induced Emission, Intramolecular

Charge

Transfer,

Twisted

Molecular

Conformation,

and

Bioimaging

Applications. Angew. Chem. Int. Edit. 2016, 55, 155-159. (10) Han, G.; Kim, D.; Park, Y.; Bouffard, J.; Kim, Y. Excimers beyond Pyrene: a Far-Red Optical Proximity Reporter and its Application to the Label-Free Detection of DNA. Angew. Chem. Int. Edit. 2015, 54, 3912-6. (11) Wang, Y.; Liu, T.; Bu, L.; Li, J.; Yang, C.; Li, X.; Tao, Y.; Yang, W. Aqueous Nanoaggregation-Enhanced One- and Two-Photon Fluorescence, Crystalline J-AggregationInduced

Red

Shift,

and

Amplified

Spontaneous

Emission

of

9,10-Bis(p-

dimethylaminostyryl)anthracene. J. Phys. Chem. C 2012, 116, 15576-15583. (12) Kaiser, T. E.; Wang, H.; Stepanenko, V.; Wuerthner, F. Supramolecular Construction of Fluorescent J-aggregates Based on Hydrogen-Bonded Perylene Dyes. Angew. Chem. Int. Edit. 2007, 46, 5541-5544. (13) Tuong Ly, K.; Chen-Cheng, R. W.; Lin, H. W.; Shiau, Y.-J.; Liu, S.-H.; Chou, P. T.; Tsao, C.-S.; Huang, Y.-C.; Chi, Y. Near-Infrared Organic Light-Emitting Diodes with very High External Quantum Efficiency and Radiance. Nature Photonics 2016, 11, 63-68. (14) Cummings, S. D.; Eisenberg, R. Tuning the Excited-State Properties of Platinum(II) Diimine Dithiolate Complexes. J. Am. Chem. Soc. 1960 118, 1949-1960. (15) Hong, Y.; Lam, J. W. Y.; Tang, B. Z. Aggregation-Induced Emission. Chem. Soc. Rev. 2011, 40, 5361-5388.


25


Page 26 of 34

(16) Mei, J.; Leung, N. L. C.; Kwok, R. T. K.; Lam, J. W. Y.; Tang, B. Z. AggregationInduced Emission: Together We Shine, United We Soar! Chem. Rev. 2015, 115, 11718-11940. (17) Beddard, G. S.; Porter, G. Concentration Quenching in Chlorophyll. Nature 1976, 260, 366-367. (18) Birks, J. B.; Christophorou, L. G. Excimer Formation in Polycyclic Hydrocarbons and their Derivatives. Nature 1963, 197, 1064. (19) Lin, M.-J.; Jimenez, A. J.; Burschka, C.; Wuerthner, F. Bay-Substituted Perylene Bisimide Dye with an Undistorted Planar Scaffold and Outstanding Solid State Fluorescence Properties. Chem. Commun. 2012, 48, 12050-12052. (20) Chiang, C. L.; Wu, M. T.; 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. (21) Li, J.; Li, Q.; Liu, D. Novel Thieno- 3,4-b -Pyrazines Cored Dendrimers with Carbazole Dendrons: Design, Synthesis, and Application in Solution-Processed Red Organic LightEmitting Diodes. ACS Appl. Mater. Interfaces 2011, 3, 2099-2107. (22) Lehrer, S. S.; Fasman, G. D. Excimer Fluorescence in Liquid Phenol, p-Ethylphenol, and Anisole. J. Am. Chem. Soc. 1965, 87, 4687-91. (23) Winnik, F. M. Photophysics of Preassociated Pyrenes in Aqueous Polymer Solutions and in Other Organized Media. Chem. Rev. 1993, 93, 587-614. (24) Forster, T. Excimers. Angew. Chem. Int. Edit. 1969, 8, 333-343.


26

Page 27 of 34 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


(25) Jagtap, S. P.; Mukhopadhyay, S.; Coropceanu, V.; Brizius, G. L.; Bredas, J.-L.; Collard, D. M. Closely Stacked Oligo(phenylene ethynylene)s: Effect of π-Stacking on the Electronic Properties of Conjugated Chromophores. J. Am. Chem. Soc. 2012, 134, 7176-7185. (26) Kim, D.; Bredas, J. L. Triplet Excimer Formation in Platinum-Based Phosphors: A Theoretical Study of the Roles of Pt-Pt Bimetallic Interactions and Interligand π-π Interactions. J. Am. Chem. Soc. 2009, 131, 11371-11380. (27) Liu, H.; Yao, L.; Li, B.; Chen, X.; Gao, Y.; Zhang, S.; Li, W.; Lu, P.; Yang, B.; Ma, Y. Excimer-Induced High-Efficiency Fluorescence due to Pairwise Anthracene Stacking in a Crystal with Long Lifetime. Chem. Commun. 2016, 52, 7356-9. (28) Shen, Y.; Liu, H.; Zhang, S.; Gao, Y.; Li, B.; Yan, Y.; Hu, Y.; Zhao, L.; Yang, B. Discrete Face-to-Face Stacking of Anthracene Inducing High-Efficiency Excimer Fluorescence in Solids via a Thermally Activated Phase Transition. J. Mater. Chem. C 2017, 5, 10061-10067. (29) Liu, H.; Dai, Y.; Gao, Y.; Gao, H.; Yao, L.; Zhang, S.; Xie, Z.; Wang, K.; Zou, B.; Yang, B., et al. Monodisperse π-π Stacking Anthracene Dimer under Pressure: Unique Fluorescence Behaviors and Experimental Determination of Interplanar Distance at Excimer Equilibrium Geometry. Adv. Opt. Mater. 2018, 6, 1800085-180090. (30) Gao, Y.; Liu, H.; Zhang, S.; Gu, Q.; Shen, Y.; Ge, Y.; Yang, B. Excimer Formation and Evolution of Excited State Properties in Discrete Dimeric Stacking of an Anthracene Derivative: a Computational Investigation. Phys. Chem. Chem. Phys. 2018, 20, 12129-12137. (31) Liu, H.; Gao, Y.; Yang, B. High-Efficiency Dimer Fluorescence System Based on π-π Interaction between Anthracenes: Recognition of Excimer. Chin. Sci. Bull. 2017, 62, 4099-4112.


27


Page 28 of 34

(32) Sekiguchi, S.; Kondo, K.; Sei, Y.; Akita, M.; Yoshizawa, M. Engineering Stacks of VShaped Polyaromatic Compounds with Alkyl Chains for Enhanced Emission in the Solid State. Angew. Chem. Int. Edit. 2016, 55, 6906-10. (33) Hisamatsu, S.; Masu, H.; Takahashi, M.; Kishikawa, K.; Kohmoto, S. Pairwise Packing of Anthracene Fluorophore: Hydrogen-Bonding-Assisted Dimer Emission in Solid State. Cryst. Growth Des. 2015, 15, 2291-2302. (34) Safont-Sempere, M. M.; Osswald, P.; Radacki, K.; Wuerthner, F. Chiral Self-Recognition and Self-Discrimination of Strapped Perylene Bisimides by π-Stacking Dimerization. Chem. Eur. J. 2010, 16, 7380-7384. (35) Safont-Sempere, M. M.; Osswald, P.; Stolte, M.; Gruene, M.; Renz, M.; Kaupp, M.; Radacki, K.; Braunschweig, H.; Wuerthner, F. Impact of Molecular Flexibility on Binding Strength and Self-Sorting of Chiral pi-Surfaces. J. Am. Chem. Soc. 2011, 133, 9580-9591. (36) Jimenez, A. J.; Lin, M.-J.; Burschka, C.; Becker, J.; Settels, V.; Engels, B.; Wuerthner, F. Structure-Property Relationships for 1,7-Diphenoxy-Perylene Bisimides in Solution and in the Solid State. Chem. Sci. 2014, 5, 608-619. (37) Nalluri, S. K. M.; Zhou, J.; Cheng, T.; Liu, Z.; Nguyen, M. T.; Chen, T.; Patel, H. A.; Krzyaniak, M. D.; Goddard, W. A.; Wasielewski, M. R., et al. Discrete Dimers of Redox-Active and Fluorescent Perylene Diimide-Based Rigid Isosceles Triangles in the Solid State. J. Am. Chem. Soc. 2018, 141, 1290-1303.


28

Page 29 of 34 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


(38) Situ, B.; Gao, M.; He, X.; Li, S.; He, B.; Guo, F.; Kang, C.; Liu, S.; Yang, L.; Jiang, M., et al. A Two-Photon AIEgen for Simultaneous Dual-Color Imaging of Atherosclerotic Plaques. Mater. Horiz. 2019, 6, 546-553. (39) Yuan, M. S.; Wang, D. E.; Xue, P.; Wang, W.; Wang, J. C.; Tu, Q.; Liu, Z.; Liu, Y.; Zhang, Y.; Wang, J. Fluorenone Organic Crystals: Two-Color Luminescence Switching and Reversible Phase Transformations between π–π Stacking-Directed Packing and Hydrogen BondDirected Packing. Chem. Mater. 2014, 26, 2467-2477. (40) Malenfant, P. R. L.; Dimitrakopoulos, C. D.; Gelorme, J. D.; Kosbar, L. L.; Graham, T. O.; Curioni, A.; Andreoni, W. N-type Organic Thin-Film Transistor with High Field-Effect Mobility Based on a N,N-'-Dialkyl-3,4,9,10-Perylene Tetracarboxylic Diimide Derivative. Appl. Phys. Lett. 2002, 80, 2517-2519. (41) Goerl, D.; Zhang, X.; Wuerthner, F. Molecular Assemblies of Perylene Bisimide Dyes in Water. Angew. Chem. Int. Edit. 2012, 51, 6328-6348. (42) Zhang, S.; Wang, X.; Huang, Y.; Zhai, H.; Liu, Z. Ammonia Sensing Properties of Perylene Diimides: Effects of Core-Substituted Chiral Groups. Sens. Actuators B 2018, 254, 805810. (43) Barnes, R. L.; Birks, J. B., 'Excimer' Fluorescence-X. Spectral Studies of 9-Methyl and 9, 10-Dimethyl Anthracene. Proc. R. Soc. A 1966, 291, 570-582. (44) Rettig, W.; Paeplow, B.; Herbst, H.; Mullen, K.; Desvergne, J. P.; Bouas-Laurent, H. Intramolecular

Excimer

Formation

in

Short-

and

Long-Chainlength

Di(9-anthryl)


29


Page 30 of 34

Bichromophoric Compounds and Relation to Ground State Properties. New J. Chem. 1999, 23, 453-460. (45) Tanaka, J. The Electronic Spectra of Aromatic Molecular Crystals. II. The Crystal Structure and Spectra of Perylene. Bull. Chem. Soc. Jpn. 1963, 36, 1237-1249. (46) Camerman, A.; Trotter, J. The Crystal and Molecular Structure of Perylene. Proc. R. Soc. A 1964, 279, 129-146. (47) Ferguson, J. Absorption and Emission Spectra of the Perylene Dimer. J. Chem. Phys. 1966, 44, 2677-2683. (48) Liu, H.; Cong, D.; Li, B.; Ye, L.; Ge, Y.; Tang, X.; Shen, Y.; Wen, Y.; Wang, J.; Zhou, C., et al. Discrete Dimeric Anthracene Stackings in Solids with Enhanced Excimer Fluorescence. Cryst. Growth Des. 2017, 17, 2945-2949. (49) Azumi, T.; McGlynn, S. P. Energy of Excimer Luminescence. I. A Reconsideration of Excimer Processes. J. Chem. Phys. 1964, 41, 3131-3138. (50) East, A. L. L.; Lim, E. C. Naphthalene Dimer: Electronic states, Excimers, and Triplet Decay. J. Chem. Phys. 2000, 113, 8981-8994. (51) Velardez, G. F. N.; Lemke, H. T.; Breiby, D. W.; Nielsen, M. M.; Møller, K. B.; Henriksen, N. E. Theoretical Investigation of Perylene Dimers and Excimers and Their Signatures in X-Ray Diffraction. J. Phys. Chem. A 2008, 112, 8179-8187. (52) Yana, D.; Shimizu, T.; Hamasaki, K.; Mihara, H.; Ueno, A. Double Naphthalene-Tagged Cyclodextrin-Peptide Capable of Exhibiting Guest-Induced Naphthalene Excimer Fluorescence. Macromol. Rapid Commun. 2002, 23, 11-15.


30

Page 31 of 34 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


(53) Spano, F. C.; Silva, C. H-and J-aggregate Behavior in Polymeric Semiconductors. Annu. Rev. Phys. Chem. 2014, 65, 477-500. (54) Hofer, L. J. E.; Grabenstetter, R. J.; Wiig, E. O. The Fluorescence of Cyanine and Related Dyes in the Monomeric State. J. Am. Chem. Soc. 1950, 72, 203-209. (55) Auweter, H.; Ramer, D.; Kunze, B.; Wolf, H. C. The Dtnamics of Excimer Formation in Perylene Crystal. Chem. Phys. Lett. 1982, 85, 325-329. (56) Lu, T.; Chen, F. Multiwfn: A Multifunctional Wavefunction Analyzer. J. Comput. Chem. 2012, 33, 580-592. (57) Cornil, J.; Beljonne, D.; Calbert, J. P.; Bredas, J. L. Interchain Interactions in Organic πConjugated Materials: Impact on Electronic Structure, Optical Response, and Charge Transport. Adv. Mater. 2001, 13, 1053-1067. (58) Li, W.; Liu, D.; Shen, F.; Ma, D.; Wang, Z.; Feng, T.; Xu, Y.; Yang, B.; Ma, Y. A Twisting Donor-Acceptor Molecule with an Intercrossed Excited State for Highly Efficient, Deep-Blue Electroluminescence. Adv. Funct. Mater. 2012, 22, 2797-2803. (59) Li, W.; Pan, Y.; Yao, L.; Liu, H.; Zhang, S.; Wang, C.; Shen, F.; Lu, P.; Yang, B.; Ma, Y. A Hybridized Local and Charge-Transfer Excited State for Highly Efficient Fluorescent OLEDs: Molecular Design, Spectral Character, and Full Exciton Utilization. Adv. Opt. Mater. 2014, 2, 892-901. (60) Li, W.; Pan, Y.; Xiao, R.; Peng, Q.; Zhang, S.; Ma, D.; Li, F.; Shen, F.; Wang, Y.; Yang, B., et al. Employing similar to 100% Excitons in OLEDs by Utilizing a Fluorescent Molecule


31


Page 32 of 34

with Hybridized Local and ChargeTransfer Excited State. Adv. Funct. Mater. 2014, 24, 16091614. (61) Zhang, S.; Yao, L.; Peng, Q.; Li, W.; Pan, Y.; Xiao, R.; Gao, Y.; Gu, C.; Wang, Z.; Lu, P., et al. Achieving a Significantly Increased Efficiency in Nondoped Pure Blue Fluorescent OLED: A Quasi-Equivalent Hybridized Excited State. Adv. Funct. Mater. 2015, 25, 1755-1762. (62) Zhang, S.; Li, W.; Yao, L.; Pan, Y.; Shen, F.; Xiao, R.; Yang, B.; Ma, Y. Enhanced Proportion of Radiative Excitons in Non-Doped Electro-Fluorescence Generated from an Imidazole Derivative with an Orthogonal Donor-Acceptor Structure. Chem. Commun. 2013, 49, 11302-11304. (63) Zhang, S.; Dai, Y.; Luo, S.; Gao, Y.; Gao, N.; Wang, K.; Zou, B.; Yang, B.; Ma, Y. Rehybridization of Nitrogen Atom Induced Photoluminescence Enhancement under Pressure Stimulation. Adv. Funct. Mater. 2017, 27, 1602276-1102284. (64) Pan, Y.; Li, W.; Zhang, S.; Yao, L.; Gu, C.; Xu, H.; Yang, B.; Ma, Y. High Yields of Singlet Excitons in Organic Electroluminescence through Two Paths of Cold and Hot Excitons. Adv. Opt. Mater. 2014, 2, 510-515. (65) Liu, H.; Bai, Q.; Yao, L.; Zhang, H.; Xu, H.; Zhang, S.; Li, W.; Gao, Y.; Li, J.; Lu, P., et al. Highly Efficient Near Ultraviolet Organic Light-Emitting Diode Based on a Meta-Linked Donor-Acceptor Molecule. Chem. Sci. 2015, 6, 3797-3804. (66) Gao, Y.; Zhang, S.; Pan, Y.; Yao, L.; Liu, H.; Guo, Y.; Gu, Q.; Yang, B.; Ma, Y. Hybridization and De-Hybridization between the Locally-Excited (LE) State and the Charge-


32

Page 33 of 34 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


Transfer (CT) State: a Combined Experimental and Theoretical Study. Phys. Chem. Chem. Phys. 2016, 18, 24176-84. (67) Zhou, C.; Cong, D.; Gao, Y.; Liu, H.; Li, J.; Zhang, S.; Su, Q.; Wu, Q.; Yang, B. Enhancing the Electroluminescent Efficiency of Acridine-Based Donor–Acceptor Materials: Quasi-Equivalent Hybridized Local and Charge-Transfer State. J. Phys. Chem. C 2018, 122, 18376-18382. (68) Van Der Weegen, R.; Korevaar, P. A.; Voudouris, P.; Voets, I. K.; de Greef, T. F. A.; Vekemans, J. A. J. M.; Meijer, E. W. Small Sized Perylene-Bisimide Assemblies Controlled by both Cooperative and Anti-Cooperative Assembly Processes. Chem. Commun. 2013, 49, 55325534. (69) Xia, J.; Chen, S.; Zou, G. Y.; Yu, Y. L.; Wang, J. H. Synthesis of Highly Stable RedEmissive Carbon Polymer Dots by Modulated Polymerization: from the Mechanism to Application in Intracellular pH Imaging. Nanoscale 2018, 10, 22484-22492. (70) Liu, J. J.; Yang, J.; Wang, J. L.; Chang, Z. F.; Li, B.; Song, W. T.; Zhao, Z.; Lou, X.; Dai, J.; Xia, F. Tetrathienylethene Based Red Aggregation-Enhanced Emission Probes: Super RedShifted Mechanochromic Behavior and Highly Photostable Cell Membrane Imaging. Mater. Chem. Front. 2018, 2, 1126-1136.

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Red Excimer Fluorescence from Dimeric

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