Anti-Kasha's Rule Emissive Switching Induced by Intermolecular H

Subscriber access provided by University of Sunderland

Article

Anti-Kasha's Rule Emissive Switching Induced by Intermolecular H-bonding Yunyun Zhou, Gleb Baryshnikov, Xuping Li, Mingjie Zhu, Hans Ågren, and Liangliang Zhu Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.8b03699 • Publication Date (Web): 18 Oct 2018 Downloaded from http://pubs.acs.org on October 19, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 9 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

Chemistry of Materials

Anti-Kasha's Rule Emissive Switching Induced by Intermolecular Hbonding Yunyun Zhou,† Gleb Baryshnikov,‡,§ Xuping Li,† Mingjie Zhu,† Hans Ågren,‡,‖ and Liangliang Zhu*,† †State

Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science, Fudan University, Shanghai 200433, China ‡Division of Theoretical Chemistry and Biology School of Biotechnology, KTH Royal Institute of Technology, SE-10691 Stockholm, Sweden §Department of Chemistry and Nanomaterials Science, Bogdan Khmelnitsky National University, Cherkasy, 18031, Ukraine ‖ Department

of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden

ABSTRACT: The exploration of emission pathways from high-excited states in organic luminogens has recently become prosperous owing to improved possibilities to study so-called anti-Kasha's rule emission with the potential of improving the luminescent quantum efficiency. However, emission pathway switching among different high-excited states has rarely been addressed through external control. We here present a rational design and synthesis of a novel azulene-based emitter to achieve a responsive control of its anti-Kasha's rule emissive switching. The emitter initially gives rise to an S3-to-S0 dominant emission as indicated by our experimental and theoretical studies. On this basis, it can be toggled into an S2-to-S0 dominant emission upon the H-bond formation between the triformyl groups and water molecules. Such a process, which originates from the H-bonding regulated distribution of excited-state energy, is accompanied with a remarkable fluorescent color conversion and a significant improvement of the fluorescent quantum yield in the azulene family. Moreover, a reversible emissive switching in doped films was observed to depend on a solid-state H-bond tuning process with moisture sensitivity. These results may provide new insight for building advanced chemical systems for visualized sensing with high distinguishability.

INTRODUCTION According to Kasha’s rule, organic luminogens normally emit from the lowest excited state irrespective of the excitation energy.1-6 In contrast, some cases (e. g. azulenes, thiones, pyrene) have been found that can produce anomalous emission from higher excited states due to their ultrafast radiative rate or large S2-S1 energy gap.7-9 These so-called anti-Kasha's rule emissions can ideally improve the fluorescent quantum efficiency by avoiding additional consumption from internal conversions and other forms of electronic relaxation processes, and are hence of great theoretical and experimental interest.1014 Although a number of prototypes that can exhibit antiKasha's rule emissions have been disclosed, thus far the emissive transfer among different high excited states has been poorly addressed, simply because these excited states basically bear quite small energy gaps in between. As a result, it has become urgent to develop a chemical strategy that can tune distinct emission from different high excited states especially from the perspective of building practical and distinguishable sensing materials. Herein, we hypothesize that a molecular design composed of precise non-covalent interactions on a well-defined luminophore can effectively achieve the above-mentioned goal. Azulene, a typical dipolar molecule consisting of an electron-deficient 7-membered ring and an electron-rich 5-

membered ring, is well known for its emission from S2 or higher states thus disobeying Kasha’s rule.15-20 However, such emission are out of external control for most of the azulene and its derivatives.21-23 It is here relevant to note that noncovalent interactions have generated large interest in the material science community, as they commonly can change the molecular optoelectronic properties as well as regulate the distribution of excited-state energy.24-29 Inspired by those facts, we here attempt to introduce H-bonding sites onto the azulene core to create a responsive emitter in which the π-π* and n-π* electronic transitions can be effectively regulated, leading to distinct and tunable emission from its high-excited states. We explore a strategy of employing intermolecular Hbonding to achieve a unimolecular emissive switching from high-excited states. Our strategy is to synthesize azulene-based emitters with different numbers of aldehyde groups directly linked with the core, namely, compound MA, DA and TA representing monoformyl, diformyl and triformyl groups connected with the azulene skeleton, respectively (see synthetic routes and chemical structures in Figure 1). Such a design takes advantage of the aldehyde groups that can form intermolecular H-bonds with polar molecules (e. g. water) to different degrees, and thus to change the distribution of the ππ* and n-π* electronic transitions as well as the corresponding radiative decay efficiency to fulfill emissive switching from high-excited states. By optimization and control studies, we

ACS Paragon Plus Environment

Chemistry of Materials 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

eventually find that compound TA can undergo a superior emissive switching between the S3-to-S0 pathway and that the S2-to-S0 one through H-bonding control is accompanied with a remarkable fluorescent color conversion between blue and green light. In this way, the anti-Kasha's rule emissions can be detected with an outstanding fluorescent quantum yield in the azulene family. Such a behavior can be utilized for a visualized moisture sensing process both in solution and in doped film, potentially revealing a distinguishable function in practical applications.

Figure 1. Molecular design and chemical strategy outline: (a) Synthetic route for the preparation of compound MA, DA and TA. (b) A proposed process for the formation of intermolecular H-bonding of compound TA upon addition of a small amount of H2O, accompanied with an anti-Kasha's rule luminescent conversion.

RESULTS AND DISCUSSION Photophysical properties upon addition of water. TA exhibits a strong emission signal as compared with MA and DA (Figure 2a), with a quantum yield (QY) up to 10 % in DMF under neutral condition. This is mainly attributed to the symmetrical structural design with triformyl groups functionalized and the relative disposition of its energy levels, despite that the molar extinction coefficient of TA is not outstanding among these compounds (Figure S10). TA initially shows a blue emission with a maximum at 416 nm together with a modest band around 465 nm. Correspondingly, the concentration related optical studies always exhibited two distinct absorption bands (Figure S11), clearly featuring this peculiar photophysical phenomenon with two independent electronic transitions at the single-molecular level. As seen from Figure 2b, interestingly, the emission bands were significantly red-shifted to give rise to a strong green emission band (~495 nm) upon addition of a small fraction of water. Such an emission wavelength shift is remarkable, resulting in an obvious luminescent color conversion along blue, cyan and green on this emitter, credited by the visualized color tuning range (see the track with red dots in the CIE diagram, Figure 2d). However, the absorption band of TA underwent a negligible change along with the alteration of the water fraction (Figure 2c). Thus, as conventional principles, like H-

or J-aggregation as well as excimer and exciplex formation, 3033 can be ruled out here, we assume that a specific emissive regulation mechanism works as we now turn to explore the structural alteration of TA.

Figure 2. Photophysical changes along with the addition of water in solution: (a) A comparison of emission spectra (λex = 365 nm) of MA, DA and TA in DMF (5×10-5 mol/L); (b) Emission spectra (λex = 365 nm) of TA in DMF (5×10-5 mol/L) with added different H2O fractions (fw); (c) UV-Vis spectra of TA (5×10-5 mol/L) in DMF/H2O mixtures with different H2O fractions; (d) CIE 1931 chromaticity diagram. The red dots signify the luminescent color coordinates for the corresponding states 1 (0.15, 0.12), 2 (0.16, 0.18), 3 (0.17, 0.29), and 4 (0.18, 0.35), insert: fluorescence photographs of TA (5×10-5 mol/L in DMF/H2O mixtures with different H2O fractions) taken under irradiation of 365 nm UV lamp.

Characterization for the intermolecular H-bonding. Upon addition of D2O into a DMSO-d6 solution of TA, the formation of H-bonding34-40 between water and TA brought in an integral shielding effect, which made an upfield shift (~ 0.05 ppm, Figure 3a) of the aromatic protons on the TA. Meanwhile, the proton resonances of TA turned broad along with the formation of the H-bonding, suggesting that an aggregation effect may also be present. Compared with TA, the proton resonances of the aldehyde groups of DA showed a faint shift (< 0.02 ppm) and all the signal peaks were still sharp upon the addition of D2O (Figure S12), indicating a very weak interaction between DA and water. In addition, FT-IR spectra showed that when the TA was transferred from 11% to 84% relative humidity (RH, Figure S13) the vibration bands of the carbanyl group and hydrogen bonded –OH functional group moved to lower wavenumbers and the absorption signal intensity decreased. These observations further indicate the formation of hydrogen bonds between the TA and H2O molecules. To study the morphological information of TA at the nanoscale, dynamic light scattering (DLS) and transmission electron microscopy (TEM) were employed to investigate a possible self-assembly. One finds that TA generally retains in the monomeric state in DMF as no effective DLS signal can be detected. After addition of a small amount of water, cluster-shaped nanoaggregates with an average diameter of 20 nm can be observed, in accordance with the peak signal (~ 24 nm) in the DLS spectra (Figure 3b). Further addition of excessive water can cause the nanoaggregates to turn into larger precipitates and another


Page 2 of 9

Page 3 of 9 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


peak appears in the DLS spectra (~ 400 nm). In the control studies, similar to the case of the TA compound, MA and DA were also monomeric in DMF and no sizable signal could be obtained. With the increase of H2O fraction, however, only small aggregates were formed (1~10 nm). The size of these aggregates thus seemingly cannot grow larger with the increase of water ratio (Figure S14) and cannot form larger clusters because of the weak hydrogen bonding. In this way, we can conclude that the triformyl groups facilitated the formation of H-bonding between the TA and water molecules, which further caused the aggregation. Actually the intermolecular H-bond clusters are responsible for the photophysical switching whereas the further formation of bigger aggregates results in luminescence quenching (vide infra). Despite that H-bonding has been a key factor to tune the luminescent color conversion of TA, no emissive shifts could, however, be observed (only with intensity quenching) for the MA and DA systems with water added (Figure S15 and S16). These control studies reflect that a relatively weak H-bonding through mono- or diformyl groups cannot sufficiently trigger the change of photophysical behavior like for TA. Although larger precipitates of TA after interacting with a big fraction of water will also quench the emission (Figure S17), the sensitivity to H-bonding formation of TA even by a tiny amount of water could be practically useful.

emission. It can suggest that the remaining part of the emission signals corresponds to those from higher lying Sn states in accordance with the relevant previous findings.15-20 The emission of TA basically exhibits a dual-band characteristic41-44 before and after addition of water, so the luminescent lifetime of each band for TA was collected. Although there is no spin multiplicity change,45-49 we still find that the τ value of the band with longer wavelength is apparently bigger than the one with shorter wavelength (Figure S18 and S19). Moreover, the excitation spectra show distinct signals monitored from two of the emission bands, respectively (Figure 4a). These results may, to some degree, signify that the dual-band characteristics origin from different electronically excited states, rather than from ordinary vibrational variations which generally are close in energy especially within highly excited states. Meanwhile, these emissions are also found stable under oxygen atmosphere (Figure S20).

Figure 4. Anti-kasha's rule emissive switching: (a) Excitation spectra (λem = 415 nm and 470 nm) of TA (5×10-5 mol/L) in DMF/H2O mixtures with different H2O fractions; (b) Proposed mechanism for the tuning of the TA luminescence in DMF/H2O mixtures; (c) Theoretically calculated orbital distributions of the HOMO and LUMO levels of TA; (d) The optimized structure for the TA hydrates that consist of 2, 4 and 6 H-bonded water molecules. Figure 3. The H-bonding formation process: (a) 1H NMR spectra (400 MHz, DMSO-d6) changes of compound TA (1×10-2 mol/L in DMSO-d6) with added different amount of D2O; (b) DLS bar graphs of TA (5×10-4 mol/L in DMF/H2O mixtures with different H2O fractions) and TEM images under a corresponding preparation condition.

Photophysical mechanism. Having established shifts for the H-bonding tuned emission, we proceed to investigate the underlying mechanism of this peculiar emissive switching behavior. Firstly, the dark nature of the S1 state can be strictly proved, since an absorption band with a wavelength of more than 600 nm can be observed without any near-infrared

To more precisely understand these experimental results, theoretical calculations50,51 were performed to probe the emissive pathways of TA as well as the switching in between. Since split emission from high-excited states have been observed for π-extended azulene derivatives because of the distinct population of the π-π* and n-π* electronic transitions,52 we can accordingly propose the dual-band characteristic of TA to a simultaneous emission from the S3 and S2 states (see models of HOMO – LUMO+1 and HOMO-2 – LUMO, respectively in Figure 4c), corresponding to π-π* and n-π* types, respectively. Such an assignment can be further confirmed by a solvatoluminescent experiment since the n-π* pathway is basically solvent polarity dependent



(Figure S21). When the S3-to-S0 emission maxima at 416 nm is initially stron, the S2-to-S0 emission (~ 465 nm) can also be observed as the S2-S3 energy band-gap (0.35 eV) seems sufficient for a slow internal conversion between these states. H-bonding provides a ~30 nm red-shift of fluorescence moving from pure DMF to that in the presence of 5% of water fraction. It can be interpreted by the H-bond/solvent relaxation due to certain charge transfer character of the nπ* transition. Simultaneously, the S4 and S5 1nπ* states become lower-lying than the S3 π-π* state, so strongly quenching the S3-to-S0 emission pathway in the presence of water (see Table S1 for the data analysis). Natural transition orbitals were also calculated for the non-hydrated MA, DA and TA species by the TDDFT/B3LYP/6-31G(d) method (see Figure S22). Meanwhile, we have further simulated few possible TA hydrates that consist of 2, 4 and 6 H-bonded water molecules (Figure 4d). For these hydrates, the energy levels for the S1 and S3 excited states of ππ* symmetry are found independent on explicit water solvent, while S4 and S5 nπ* states become red-shifted in agreement with experiment data and above proposed dual fluorescence mechanism for TA. In contrast, the H-bonding effect is not sufficient for the shifting of the dark nπ* states to become lower than the S3 ππ* state in DA. For the MA molecule, only the one nπ* state (S2 state) exists in its spectrum because of the presence of only one CHO group. Thus, emissive switching can only be effectively achieved in TA among these comparisons (see Jablonski diagram for a proposed emissive mechanism in Figure 4b and in Figure S23). In addition, we need to emphasize that such an emissive switching can only be aroused by intermolecular H-bond clusters (i. e. TA interact with water molecules in between) as illustrated in Figure 1b. No remarkable shift and switching of emissions can be observed when TA was exposed to methanol (Figure S24 and Figure S25), probably due to lack of amplification effect without cluster formation. The 1H NMR spectra of TA in DMSO-d6 also showed that there was no obvious peak shift of the aromatic protons with the addition of methanol-d4 but the peak of H2O shifted downfield due to the formation of Hbondswith methanol (Figure S26). Moreover, the ethylene glycol which has two –OH groups also affected little on the absorption and emission of TA in DMF (Figure S27), probably due to the weak H-bonding force. Thus, owing to the uniquely selective response to water, TA may be suitable for the usage of a moisture sensing. Moisture sensing in the solid state. Thus, tunable luminescent color conversion along blue, cyan, and green from high-excited states on the TA emitter have been convincingly achieved by H-bonding control. The behavior of the corresponding solid-state emission tuning was also explored for this material. In our case, the hydrophilic polymers polyvinyl alcohol (PVA) and polyacrylic acid sodium salt (PAAS) were considered for an optimized matrix to ensure a sufficient moisture sensitivity (Figure S28). Similar emissive switching behavior was observed for a TA doped PVA/PAAS film (Figure 5) and both the emission intensity and wavelength changed along with the interaction of water, featuring an analogous anti-Kasha's rule emissive switching relying on a solid-state H-bond formation process. Interestingly, as such a doped film is quite sensitive to a tiny amount of water, our system can be developed into a

visualized humidity detection material (see Figure 5a).53-56 Reversible and repeated operations in a film can be more convenient than in solution (Figure 5b). On the other hand, water dropping onto the doped film can cause more dramatic emissive property change as well as a final quenching effect. However, it can be completely recovered to an original state with a drying process (Figure 5c, 5d and S29). Existing visualized water sensing approaches have been based on electrochemical photo-induced electron transfer (PET)57,58, intramolecular charge transfer (ICT)59 and excited state intramolecular proton transfer (ESIPT)60 processes on those large conjugated backbones or incorporated luminophores. This is the first visualized sensing example relying on highexcited state regulation, featuring a well distinguishable function with strong luminescence and anti-Kasha's rule emissive switching. Moreover, there are three aldehyde groups directly linked with azulene core, which is a a highly efficient H-bond receptor for a generalized control in a relatively simple structure.

Figure 5. Visualized sensing study with the addition of water in doped films: (a) Emission spectra (λex = 365 nm) changes of TA doped PVA/PAAS film in 84 % RH and 11 % RH moisture chamber for different times; (b) Reversible change in the emission intensity by varying the RH; (c) The maximum emission (λex = 365 nm) changes of TA doped PVA/PAAS film with dropped 5 μL H2O on it. The balls represent the relationship between maximum emission (including peak position and intensity) and the status in prolonging the time, and the ball color represents the luminescence color and the size represents the corresponding state; (d) The writing of “Z” character with H2O onto the TA doped PVA/PAAS film on a quartz substrate and the process of the three state recyclable (photographs were taken under 365 nm UV light).

CONCLUSIONS We have demonstrated that an azulene-based emitter can undergo an unprecedented emissive switching of high excited states (anti-Kasha's rule emission) through intermolecular Hbonding control. Molecular engineering with an appropriate modification of the triformyl groups onto the azulene core played here a key role, thus to effectively regulate the distribution of the π-π* and n-π* electronic transitions as well as the corresponding radiative decay efficiency. Overall, the photophysical switching arises from stabilization of the CT


Page 4 of 9

Page 5 of 9 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


excited state by the polar solvent. The “electronic” effect of Hbonding is here more pronounced than its rigidity effect as indicated by the current photophysical studies. Such a process, alongwith a superior fluorescent intensity, was accompanied with a remarkable fluorescent color conversion between blue and green light, representing a highly distinguishable moisture sensing behavior not only in solution but also in the solid state. We believe that the study herein could be valuable for further exploration of more intrinsic photophysical properties of organic functional molecules and materials, as well as for expanding their related applications.

EXPERIMENTAL SECTION General. 1H NMR and 13C NMR spectra were measured on a Bruker 400L spectrometer. High resolution mass spectrometry (HRMS) data was measured using a Matrix Assisted Laser Desorption Ionization-Time of Flight/Time of Flight Mass Spectrometer (5800). The UV-Vis absorption spectra were recorded on a Shimadzu 1800 spectrophotometer. The emission spectra were recorded on a Shimadzu RF5301PC spectrofluorophotometer or FLS920 from Edinburgh Instruments Ltd. The quantum yield was measured by QM40 from Photo Technology International, Inc. (PTI, USA). Fourier transform infrared (FTIR) spectroscopy was carried out within KBr slices in the 4000-400 cm-1 range using a Nicolet 6700 infrared spectrum radiometer. The photographs were taken using a RY-WFH-203B UV lamp (8 W) with the irradiation wavelength of 365 nm. Transmission electron microscopy (TEM) was performed on a Jeol JEM 2100 with an accelerating voltage of 200 kV. The samples were prepared by drop-casting samples onto 300 mesh carbon grids on a copper support. Materials. n-bromobutane, pyridine-4-carboxaldehyde, ptoluenesulfonic acid, sodium polymethacrylate (PAAS), NaOH were purchased from Energy Chemical and used as received. Cyclopentadiene, HCl (aq), NaH, phosphoryl trichloride and pyrophosphoryl chloride were purchased from Sinopharm Chemical Reagent Co., Ltd and used as received. Ethanol, DMF, CH2Cl2, petroleum ether and ethyl acetate were purchased from Tansoole and used as received. Polyvinyl alcohol (PVA) was purchased from Adamas-beta® and Tokyo Chemical Industry Co., Ltd. Cyclopentadiene was distilled before use. Synthesis of compound MA. The preparation for MA was carried out according to the procedure described in literature.18 Synthesis of compound DA. Phosphoryl trichloride (1.1 mL, 12 mmol) was added to anhydrous DMF (5 mL) very slowly at 0°C and the mixture was stirred for 30 min before MA (1.56 g, 10 mmol) was added to the reaction system. The reaction mixture was allowed to warm to room temperature and the stirring was maintained for additional 3 h. When the completion of the reaction was indicated by TLC, the reaction was quenched by addition of 10 % aqueous NaOH (20 mL) and 10 min successive stirring. Then the mixture was extracted with ethyl acetate (3  30 mL) and the combined organic phase was washed by brine. After drying over Na2SO4, the solvent was removed under reduced pressure to afford the compound DA as a green solid (1.38 g, 75 %). 1H NMR (400 MHz, CDCl3) δ 10.43 (s, 1H), 10.19 (s, 1H), 9.76 (d, J = 9.8 Hz, 1H), 8.68 (d, J = 10.0 Hz, 1H), 8.47 (d, J = 4.1 Hz, 1H),

8.11 (dd, J = 9.8, 1.4 Hz, 1H), 8.06 (dd, J = 10.0, 1.4 Hz, 1H), 7.48 (d, J = 4.1 Hz, 1H). 13C NMR (101 MHz, CDCl3) δ 193.54, 186.68, 146.79, 145.80, 141.87, 141.59, 138.06, 136.45, 130.97, 127.12, 127.08, 120.63. HRMS m/z: [M + H] + calcd for C12H9O2+, 185.0597; found, 185.1593. Synthesis of compound TA. Pyrophosphoryl chloride (0.83 mL, 6 mmol) was added to anhydrous DMF (1 mL) very slowly at 0°C and the mixture was stirred for 30 min, then DA (0.925 g, 5 mmol) was dissolved in CH2Cl2 and added to the reaction system. The reaction mixture was heated to 40 ℃ and maintained for additional 1 h. When the reaction was completed, 10 % aqueous NaOH (20 mL) was added to quenched the reaction. The mixture was extracted with CH2Cl2 (3  30 mL) and the combined organic phase was washed by brine. After drying over Na2SO4, the solvent was removed under reduced pressure, and the residue was further purified twice by column chromatography (petroleum ether : ethyl acetate = 5 : 1, v/v) to afford the compound TA as a green solid (0.11 g, 10 %). 1H NMR (400 MHz, CDCl3) δ 10.43 (s, 2H), 10.28 (s, 1H), 10.05 (d, J = 10.6 Hz, 2H), 8.82 (s, 1H), 8.41 (d, J = 10.7 Hz, 2H). 13C NMR (101 MHz, CDCl3) δ 192.49, 186.95, 150.59, 145.13, 143.68, 139.70, 133.52, 126.77. HRMS m/z: [M + H] + calcd for C13H9O3+, 213.0546; found, 213.1403. Preparation of humidity-sensitive materials (TA doped PVA/PAAS film): TA was first dissolved in THF to form a 1 mg/mL stock solution (5 mM). Then, 10 μL of TA solution was added to a mixture of polyvinyl alcohol (PVA) and sodium polymethacrylate (PAAS), and the overall weight was 100 mg. 3 mL of water was added and the mixture was stirring vigorously for 1 h at 80 ℃. The resulting solution was dropcoated on quartz glass slides followed by heating in oven (RH 10 %) to obtain dry TA PVA/PAAS film. Self-made moisture chamber using saturated salt solutions were used for RH control. The slides were then placed in the moisture chamber and sealed for 30 min at room temperature for next studies. Transmission Electron Microscopy (TEM). The TA (5 × 10-4 mol/L in DMF/H2O) was placed on a copper grid coated with a super thin carbon film and dried under an electric vacuum oven. The microscopic images were obtained by field emission transmission electron microscopy (FE-TEM, JEOL, JEM2100F) with an accelerating voltage of 200 kV. Computational details. The molecule of azulene-1,3,6tricarbaldehyde (TA) has been optimized by the B3LYP/631G(d) method61-63 using the polarizable continuum model to take into account the solvent effects on the initial structural parameters. All the chosen solvents provide negligible changes on the structure of TA and that is why we have used the gasphase optimized initial atomic coordinates for the next computations. The vertical absorption spectrum for the singletsinglet transitions has been calculated within time-dependent (TD) DFT method64 using the same B3LYP/6-31G(d) approximation and PCM solvent model65 (DCM, DMF and H2O). The excited-state optimized geometries and corresponding fluorescence wave-length have been calculated at the same level of TDDFT theory using the state-specific procedure. An additional calculation for the electronic absorption spectrum of TA has been carried out by the secondorder approximate coupled cluster singles and doubles (CC2)66 method using Def2-TZVP67 basis set. All DFT and TD DFT computations were carried out within Gaussian16 program



package.68 CC2 calculations were performed using Turbomole software.69

ASSOCIATED CONTENT Supporting Information. Experimental details, additional computational data, additional photophysical properties, NMR spectra and Maldi-Tof mass spectra. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author * [email protected] (ORCID: 0000-0001-6268-3351)

Author Contributions All authors have given approval to the final version of the manuscript.

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This work was supported by the NSFC/China (21628401, 21644005), and partially from the National Key Research and Development Program of China (2017YFA0207700). The calculations were performed with computational resources provided by the High Performance Computing Center North (HPC2N) in Umeå, Sweden, through the project ‘‘Multiphysics Modeling of Molecular Materials” SNIC 2017-12-49. H. A. and G. B. acknowledge the Carl Tryggers foundation (Grant No. CTS 16:536 and 17:514). G. B. also acknowledges the Ministry of Education and Science of Ukraine (project numbers 0117U003908 and 0118U003862).

REFERENCES (1) Kasha, M., Characterization of electronic transitions in complex molecules. Discuss. Faraday Soc. 1950, 9, 14-19. (2) Freed, K. F., Radiationless transitions in molecules. Acc. Chem. Res. 1978, 11, 74-80. (3) Itoh, T., Fluorescence and phosphorescence from higher excited states of organic molecules. Chem. Rev. 2012, 112, 45414568. (4) Tilley, A. J.; Pensack, R. D.; Lee, T. S.; Djukic, B.; Scholes, G. D.; Seferos, D. S., Ultrafast Triplet Formation in Thionated Perylene Diimides. J Phys. Chem. C 2014, 118, 999610004. (5) Zhang, Q.; Li, J.; Shizu, K.; Huang, S.; Hirata, S.; Miyazaki, H.; Adachi, C., Design of Efficient Thermally Activated Delayed Fluorescence Materials for Pure Blue Organic Light Emitting Diodes. J. Am. Chem. Soc. 2012, 134, 14706-14709. (6) Shen, X.; Runfeng, C.; Chao, Z.; Wei, H., Excited State Modulation for Organic Afterglow: Materials and Applications. Adv. Mater. 2016, 28, 9920-9940. (7) Yushchenko, O.; Licari, G.; Mosquera-Vazquez, S.; Sakai, N.; Matile, S.; Vauthey, E., Ultrafast Intersystem-Crossing Dynamics and Breakdown of the Kasha-Vavilov's Rule of Naphthalenediimides. J Phys. Chem. Lett. 2015, 6, 2096-100. (8) Nenov, A.; Borrego-Varillas, R.; Oriana, A.; Ganzer, L.; Segatta, F.; Conti, I.; Segarra-Marti, J.; Omachi, J.; Dapor, M.; Taioli, S.; Manzoni, C.; Mukamel, S.; Cerullo, G.; Garavelli, M., UV-LightInduced Vibrational Coherences: The Key to Understand Kasha Rule Violation in trans-Azobenzene. J. Phys. Chem. Lett. 2018, 9, 15341541.

(9) Qian, H.; Cousins, M. E.; Horak, E. H.; Wakefield, A.; Liptak, M. D.; Aprahamian, I., Suppression of Kasha's rule as a mechanism for fluorescent molecular rotors and aggregation-induced emission. Nat. Chem. 2017, 9, 83-87. (10) Itoh, T., Intramolecular mechanisms for the occurrence of fluorescence from upper excited states of aromatic molecules and linear polyenes. Rev. Fluoresc. 2016, 8, 213-234. (11) Demchenko, A. P.; Tomin, V. I.; Chou, P.-T., Breaking the Kasha Rule for More Efficient Photochemistry. Chem. Rev. 2017, 117, 13353 - 13381. (12) Letrun, R.; Vauthey, E., Excitation Wavelength Dependence of the Dynamics of Bimolecular Photoinduced Electron Transfer Reactions. J. Phys. Chem. Lett. 2014, 5, 1685-1690. (13) Maciejewski, A.; Steer, R. P., The photophysics, physical photochemistry, and related spectroscopy of thiocarbonyls. Chem. Rev. 1993, 93, 67-98. (14) Blice ‐ Baum, A.; Dyke, A. V.; Sigmon, I.; Salter, E. A.; Wierzbicki, A.; Pocker, Y.; Spyridis, G. T., Computational and spectroscopic studies concerning the solvatochromic behavior of 1,3‐disubstituted azulenes. Int. J Quantum Chem. 2006, 106, 23312338. (15) Murata, S.; Iwanaga, C.; Toda, T.; Kokubun, H., Fluorescence yields of azulene derivatives. Chem. Phys. Lett. 1972, 13, 101-104. (16) Griesser, H. J.; Wild, U. P., The fluorescence lifetimes of carbonyl derivatives of azulene showing dual emission. J Photoch. 1980, 13, 309-318. (17) Zhou, Y.; Zhuang, Y.; Li, X.; Agren, H.; Yu, L.; Ding, J.; Zhu, L., Selective Dual-Channel Imaging on Cyanostyryl-Modified Azulene Systems with Unimolecularly Tunable Visible-Near Infrared Luminescence. Chem. Eur. J. 2017, 23, 7642-7647. (18) Zhou, Y.; Zou, Q.; Qiu, J.; Wang, L.; Zhu, L., Rational Design of a Green-Light-Mediated Unimolecular Platform for Fast Switchable Acidic Sensing. J Phys. Chem. Lett. 2018, 9, 550-556. (19) Murai, M.; Ku, S.-Y.; Treat, N. D.; Robb, M. J.; Chabinyc, M. L.; Hawker, C. J., Modulating structure and properties in organic chromophores: influence of azulene as a building block. Chem. Sci. 2014, 5, 3753-3760. (20) Hanshen, X.; Xike, G., Application of Azulene in Constructing Organic Optoelectronic Materials: New Tricks for an Old Dog. ChemPlusChem 2017, 82, 945-956. (21) Lambert, C.; Noll, G.; Zabel, M.; Hampel, F.; Schmalzlin, E.; Brauchle, C.; Meerholz, K., Highly substituted azulene dyes as multifunctional NLO and electron-transfer compounds. Chem. Eur. J. 2003, 9, 4232-9. (22) Cristian, L.; Sasaki, I.; Lacroix, P. G.; Donnadieu, B.; Asselberghs, I.; Clays, K.; Razus, A. C., Donating Strength of Azulene in Various Azulen-1-yl-Substituted Cationic Dyes: Application in Nonlinear Optics. Chem. Materials 2004, 16, 3543-3551. (23) Makinoshima, T.; Fujitsuka, M.; Sasaki, M.; Araki, Y.; Ito, O.; Ito, S.; Morita, N., Competition between Intramolecular ElectronTransfer and Energy-Transfer Processes in Photoexcited Azulene − C60Dyad. J Phys. Chem. A 2004, 108, 368-375. (24) Zhou, H.; Xue, C.; Weis, P.; Suzuki, Y.; Huang, S.; Koynov, K.; Auernhammer, G. K.; Berger, R.; Butt, H.-J.; Wu, S., Photoswitching of glass transition temperatures of azobenzenecontaining polymers induces reversible solid-to-liquid transitions. Nat. Chem. 2016, 9, 145-151. (25) Hestand, N. J.; Kazantsev, R. V.; Weingarten, A. S.; Palmer, L. C.; Stupp, S. I.; Spano, F. C., Extended-Charge-Transfer Excitons in Crystalline Supramolecular Photocatalytic Scaffolds. J. Am. Chem. Soc. 2016, 138, 11762-11774. (26) Sato, K.; Ji, W.; Palmer, L. C.; Weber, B.; Barz, M.; Stupp, S. I., Programmable Assembly of Peptide Amphiphile via Noncovalent-to-Covalent Bond Conversion. J. Am. Chem. Soc. 2017, 139, 8995-9000. (27) Yanagisawa, Y.; Nan, Y.; Okuro, K.; Aida, T.,


Page 6 of 9

Page 7 of 9 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


Mechanically robust, readily repairable polymers via tailored noncovalent cross-linking. Science 2018, 359, 72-76. (28) Wu, G.; Chen, S.-C.; Liu, C.-L.; Wang, Y.-Z., Direct Aqueous Self-Assembly of an Amphiphilic Diblock Copolymer toward Multistimuli-Responsive Fluorescent Anisotropic Micelles. ACS Nano 2015, 9, 4649 - 4659. (29) Cheung, S.; O'Shea, D. F., Directed self-Assembly of fluorescence responsive nanoparticles and their use for real-Time surface and cellular imaging. Nat. commun. 2017, 8, 1885-1897. (30) Hirose, T.; Tsunoi, Y.; Fujimori, Y.; Matsuda, K., Fluorescence enhancement of covalently linked 1-cyano-1,2diphenylethene chromophores with naphthalene-1,8-diyl linker units: analysis based on kinetic constants. Chem. Eur. J. 2015, 21, 1637-44. (31) Ghosh, S.; Li, X.-Q.; Stepanenko, V.; Wuerthner, F., Control of H- and J-type π stacking by peripheral alkyl chains and self-sorting phenomena in perylene bisimide homo- and heteroaggregates. Chem. Eur. J. 2008, 14, 11343-11357. (32) Eisfeld, A.; Briggs, J. S., The J- and H-bands of organic dye aggregates. Chem. Phys. 2006, 324, 376-384. (33) An, B.-K.; Kwon, S.-K.; Jung, S.-D.; Park, S. Y., Enhanced emission and its switching in fluorescent organic nanoparticles. J. Am. Chem. Soc. 2002, 124, 14410-14415. (34) Yan, X.; Jiang, B.; Cook, T. R.; Zhang, Y.; Li, J.; Yu, Y.; Huang, F.; Yang, H.-B.; Stang, P. J., Dendronized organoplatinum(II) metallacyclic polymers constructed by hierarchical coordinationdriven self-assembly and hydrogen-bonding interfaces. J. Am. Chem. Soc. 2013, 135, 16813 - 16816. (35) Ma, C.; Ou, Y.-Q.; Chan, C. T.-L.; Wong, A. K.-W.; Chan, R. C.-T.; Chung, B. P.-Y.; Jiang, C.; Wang, M.-L.; Kwok, W.-M., Nonradiative dynamics determined by charge transfer induced hydrogen bonding: a combined femtosecond time-resolved fluorescence and density functional theoretical study of methyl dimethylaminobenzoate in water. Phys. Chem. Chem. Phys. 2018, 20, 1240-1251. (36) Chen, Y.; Zhang, W.; Zhao, Z.; Cai, Y.; Gong, J.; Kwok, R. T. K.; Lam, J. W. Y.; Sung, H. H. Y.; Williams, I. D.; Tang, B. Z., An Easily Accessible Ionic Aggregation-Induced Emission Luminogen with Hydrogen-Bonding-Switchable Emission and Wash-Free Imaging Ability. Angew. Chem., Int. Ed. 2018, 57, 5011-5015. (37) Zhu, L.; Tran, H.; Beyer, F. L.; Walck, S. D.; Li, X.; Agren, H.; Killops, K. L.; Campos, L. M., Engineering topochemical polymerizations using block copolymer templates. J. Am. Chem. Soc. 2014, 136, 13381-7. (38) Zhu, L.; Trinh, M. T.; Yin, L.; Zhang, Z., Sequential oligodiacetylene formation for progressive luminescent color conversion via co-micellar strategy. Chem. Sci. 2016, 7, 2058-2065. (39) de Greef, T. F. A.; Meijer, E. W., Supramolecular polymers. Nature 2008, 453, 171-173. (40) Tang, T.; Lin, T.; Wang, F.; He, C., Origin of Near-Infrared Absorption for Azulene-Containing Conjugated Polymers upon Protonation or Oxidation. J Phys. Chem. B 2015, 119, 8176-8183. (41) Zhao, Y.; Shi, C.; Yang, X.; Shen, B.; Sun, Y.; Chen, Y.; Xu, X.; Sun, H.; Yu, K.; Yang, B.; Lin, Q., pH- and TemperatureSensitive Hydrogel Nanoparticles with Dual Photoluminescence for Bioprobes. ACS Nano 2016, 10, 5856-5863. (42) Xie, Z.; Huang, Q.; Yu, T.; Wang, L.; Mao, Z.; Li, W.; Yang, Z.; Zhang, Y.; Liu, S.; Xu, J.; Chi, Z.; Aldred, M. P., Hydrogen-Bonding-Assisted Intermolecular Charge Transfer: A New Strategy to Design Single-Component White-Light-Emitting Materials. Adv. Funct. Mater. 2017, 27, 1703918-1703928. (43) Wu, Y.-T.; Shanmugam, C.; Tseng, W.-B.; Hiseh, M.-M.; Tseng, W.-L., A gold nanocluster-based fluorescent probe for simultaneous pH and temperature sensing and its application to cellular imaging and logic gates. Nanoscale 2016, 8, 11210-11216. (44) Kawagoe, R.; Takashima, I.; Uchinomiya, S.; Ojida, A., Reversible ratiometric detection of highly reactive hydropersulfides using a FRET-based dual emission fluorescent probe. Chem. Sci. 2017, 8, 1134-1140.

(45) Wu, H.; Zhou, Y.; Yin, L.; Hang, C.; Li, X.; Agren, H.; Yi, T.; Zhang, Q.; Zhu, L., Helical Self-Assembly-Induced Singlet-Triplet Emissive Switching in a Mechanically Sensitive System. J. Am. Chem. Soc. 2017, 139, 785-791. (46) Yang, J.; Ren, Z.; Xie, Z.; Liu, Y.; Wang, C.; Xie, Y.; Peng, Q.; Xu, B.; Tian, W.; Zhang, F.; Chi, Z.; Li, Q.; Li, Z., AIEgen with Fluorescence-Phosphorescence Dual Mechanoluminescence at Room Temperature. Angew. Chem., Int. Ed. 2017, 56, 880-884. (47) Wei, J.; Liang, B.; Duan, R.; Cheng, Z.; Li, C.; Zhou, T.; Yi, Y.; Wang, Y., Induction of Strong Long-Lived RoomTemperature Phosphorescence of N-Phenyl-2-naphthylamine Molecules by Confinement in a Crystalline Dibromobiphenyl Matrix. Angew. Chem., Int. Ed. 2016, 55, 15589-15593. (48) Li, D.; Lu, F.; Wang, J.; Hu, W.; Cao, X.-M.; Ma, X.; Tian, H., Amorphous Metal-Free Room-Temperature Phosphorescent Small Molecules with Multicolor Photoluminescence via a Host-Guest and Dual-Emission Strategy. J. Am. Chem. Soc. 2018, 140, 1916-1923. (49) Gong, Y.; Chen, G.; Peng, Q.; Yuan, W. Z.; Xie, Y.; Li, S.; Zhang, Y.; Tang, B. Z., Achieving Persistent Room Temperature Phosphorescence and Remarkable Mechanochromism from Pure Organic Luminogens. Adv. Mater. 2015, 27, 6195-6201. (50) Baryshnikov, G.; Minaev, B.; Ågren, H., Theory and Calculation of the Phosphorescence Phenomenon. Chem. Rev. 2017, 117, 6500-6537. (51) Li, X.; Zhu, L.; Duan, S.; Zhao, Y.; Agren, H., Aggregation-induced chiral symmetry breaking of a naphthalimidecyanostilbene dyad. Phys. Chem. Chem. Phys. 2014, 16, 2385423860. (52) Holzwarth, A. R.; Razi Naqvi, K.; Wild, U. P., Slow internal conversion between two close lying singlet states in a large molecule: azuleno[5,6,7-cd]phenalene. Chem. Phys. Lett. 1977, 46, 473-476. (53) Cheng, Y.; Wang, J.; Qiu, Z.; Zheng, X.; Leung, N. L. C.; Lam, J. W. Y.; Tang, B. Z., Multiscale Humidity Visualization by Environmentally Sensitive Fluorescent Molecular Rotors. Adv. Mater. 2017, 29, 1703900-1703907. (54) Wang, A.; Fan, R.; Dong, Y.; Song, Y.; Zhou, Y.; Zheng, J.; Du, X.; Xing, K.; Yang, Y., Novel Hydrogen-Bonding CrossLinking Aggregation-Induced Emission: Water as a Fluorescent "Ribbon" Detected in a Wide Range. ACS Appl. Mater. Interfaces 2017, 9, 15744-15757. (55) Park, D.-H.; Jeong, W.; Seo, M.; Park, B. J.; Kim, J.-M., Inkjet-Printable Amphiphilic Polydiacetylene Precursor for Hydrochromic Imaging on Paper. Adv. Funct. Mater. 2016, 26, 498506. (56) Lee, J.; Pyo, M.; Lee, S.-h.; Kim, J.; Ra, M.; Kim, W.-Y.; Park, B. J.; Lee, C. W.; Kim, J.-M., Hydrochromic conjugated polymers for human sweat pore mapping. Nat. Commun. 2014, 5, 3736. (57) Ooyama, Y.; Matsugasako, A.; Oka, K.; Nagano, T.; Sumomogi, M.; Komaguchi, K.; Imae, I.; Harima, Y., Fluorescence PET (photo-induced electron transfer) sensors for water based on anthracene-boronic acid ester. Chem. Commun. 2011, 47, 4448-4450. (58) Ooyama, Y.; Furue, K.; Uenaka, K.; Ohshita, J., Development of highly-sensitive fluorescence PET (photo-induced electron transfer) sensor for water: anthracene-boronic acid ester. RSC Adv. 2014, 4, 25330-25333. (59) Niu, C.; Li, L.; Qin, P.; Zeng, G.; Zhang, Y., Determination of Water Content in Organic Solvents by Naphthalimide Derivative Fluorescent Probe. Anal. Sci. 2010, 26, 671-674. (60) Zhao, J.; Ji, S.; Chen, Y.; Guo, H.; Yang, P., Excited state intramolecular proton transfer (ESIPT): from principal photophysics to the development of new chromophores and applications in fluorescent molecular probes and luminescent materials. Phys. Chem. Chem. Phys. 2012, 14, 8803-8817. (61) Becke, A. D., Density-functional exchange-energy approximation with correct asymptotic behavior. Phys. Rev. A 1988, 38, 3098-3100.



(62) Lee, C.; Yang, W.; Parr, R. G., Development of the ColleSalvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B 1988, 37, 785-789. (63) Michelle M. Francl, W. J. P., Warren J. Hehre, J. Stephen Binkley, D. J. DeFrees, and Pople, J. A., Self‐consistent molecular orbital methods. XXIII. A polarization‐type basis set for second‐row elements. J. Chem. Phys. 1982, 77, 3654-3665. (64) Runge, E.; Gross, E. K. U., Density-Functional Theory for Time-Dependent Systems. Phys. Rev. Lett. 1984, 52, 997-1000. (65) Miertuš, S.; Scrocco, E.; Tomasi, J., Electrostatic interaction of a solute with a continuum. A direct utilizaion of AB initio molecular potentials for the prevision of solvent effects. Chem. Phys. 1981, 55, 117-129. (66) Christiansen, O.; Koch, H.; Jørgensen, P., The secondorder approximate coupled cluster singles and doubles model CC2. Chem. Phys. Lett. 1995, 243, 409-418. (67) Weigend, F.; Ahlrichs, R., Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: Design and assessment of accuracy. Phys. Chem. Chem. Phys. 2005, 7, 3297-3305. (68) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; et al. Gaussian, Inc., Wallingford CT, 2016, Gaussian 16, Revision A.03. (69) Filipp, F.; Reinhart, A.; Christof, H.; Wim, K.; Marek, S.; Florian, W., Turbomole. WIREs Comput. Mol. Sci. 2014, 4, 91-100.


Page 8 of 9

Page 9 of 9 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


Table of Contents (TOC)


Anti-Kasha's Rule Emissive Switching Induced by Intermolecular H

Recommend Documents