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Cite This: J. Phys. Chem. C XXXX, XXX, XXX-XXX

Inter- and Intramolecular Electron-Transfer Reduction Properties of Coronenediimide Derivatives via Photoinduced Processes Motoki Yoshida,† Hayato Sakai,† Kei Ohkubo,‡ Shunichi Fukuzumi,*,§,∥ and Taku Hasobe*,† †

Department of Chemistry, Faculty of Science and Technology, Keio University, Yokohama 223-8522, Japan Institute for Advanced Co-Creation Studies, Open and Transdisciplinary Research Initiatives, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan § Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Korea ∥ Faculty of Science and Engineering, Meijo University, SENTAN, Japan Science and Technology Agency (JST), Nagoya, Aichi 468-0073, Japan ‡

S Supporting Information *

ABSTRACT: Coronenediimide derivatives with five- or six-membered maleimide groups [denoted as Cor(5Im)2 and Cor(6Im)2] were employed as electron acceptors to examine the electron-transfer reduction properties through photochemical and electrochemical measurements. In steady-state absorption and fluorescence measurements, the spectra of Cor(5Im)2 and Cor(6Im)2 became remarkably broadened and red-shifted as compared to pristine coronene (Cor). These results are supported by electrochemical measurements and DFT calculations. The rate constants of photoinduced intermolecular electron transfer from various donor molecules to 3Cor(5Im)2* or 3Cor(6Im)2* are determined by nanosecond transient absorption measurements. Although the back-electron-transfer reactions examined in this study proceed with the diffusion-limited rate constant in benzonitrile (PhCN), the rate constants of forward electron-transfer reactions (ket) increase with an increase in the driving force of electron transfer (−ΔGet) to approach the diffusion-limited rate constant. When the driving force dependence of ket was fit on the basis of the Marcus theory of electron transfer, the reorganization energy (λ) of the electrontransfer reduction of Cor(5Im)2 and Cor(6Im)2 are determined to be 0.77 and 1.15 eV, respectively. A new covalently perylenelinked donor−acceptor dyad was also synthesized to investigate the dynamics of ultrafast photoinduced intramolecular electron transfer.



INTRODUCTION In recent years, increasing attention has been paid to the disklike polycyclic aromatic hydrocarbons (PAHs) such as perylene and coronene because of their efficient UV/visible light absorption and high electron density, which are related to the extended π-conjugation.1 The supramolecular structures formed by π-stacking of PAHs derivatives have also been shown to exhibit one-dimensional charge-carrier mobilities along the stacking axis.2,3 Thus, PAHs have emerged as promising semiconductor materials for organic electronics including field-effect transistors (FETs)4−9 and solar cells.10−16 Although synthesis and properties of p-type organic semiconductor materials have been widely reported,17−27 the development of n-type organic semiconductors has lagged behind that of p-type semiconductors. Generally, synthesis of ntype organic semiconductors is achieved by introducing electron-accepting substituents and/or electronegative moieties onto the peripheral positions of a PAH aromatic core.28 However, most studies regarding electron acceptors have been limited to perylenediimide (PDI)29−41 and fullerene derivatives.42−55 Broadening the collection of electron acceptors © XXXX American Chemical Society

composed of PAHs is thus of great importance to develop the possibilities of PAHs as promising materials for organic electronics. Rational synthesis of coroneneimide derivatives has been recently reported.56 When the chemical structures of coronene are compared with that of perylene, one of the advantageous points is the synthetic diversity of coroneneimide because up to four maleimide groups can be introduced to a coronene core in the case of coroneneimides, in contrast with only two maleimide groups in the case of PDI.57 The photophysical and electrochemical properties of coroneneimides can be accordingly controlled by the type and number of substituents.58−60 Nevertheless, the number of reports on the photoinduced electron-transfer reduction of coroneneimides61 is extremely limited as compared to that of PDIs, and the detailed electron-transfer properties of coroneneimide derivaSpecial Issue: Prashant V. Kamat Festschrift Received: October 4, 2017 Revised: October 30, 2017 Published: October 30, 2017 A

DOI: 10.1021/acs.jpcc.7b09817 J. Phys. Chem. C XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry C Chart 1. Chemical Structures of Coroneneimide and Perylene Derivatives in This Study

Preparative thin layer chromatography was performed on glass plates coated with silica gel 60 F254 (Merck). Preparative recycling gel permeation chromatography was performed with a high pressure liquid chromatography apparatus from Japan Analytical Industry (LC-9204) using chloroform as eluent at room temperature. The LC-9204 apparatus was equipped with a pump (JAI PI-60, flow rate 2.5 mL/min), a UV detector (JAI UV-3740), and two columns (JAIGEL 2H and 1H, 40 × 600 mm for each). 1H NMR and 13C NMR spectra were acquired in CDCl3 on a JEOL ECX-400, AL-400, or ALPHA-400 spectrometer, using the solvent peak as the reference standard, with chemical shifts given in parts per million. MALDI-TOF mass spectra were recorded on Bruker Ultra flex. The density functional theory (DFT) calculations of molecular orbitals were performed with Gaussian 09 program and at B3LYP/6-31G* and M06-2X/6-31+G(d,p) level of theory. The molecular geometries were optimized at the same level. The details on spectroscopic and electrochemical measurements are shown in the Supporting Information. Synthesis of Compound 2. Compound 1 (19.3 g, 27.9 mmol), 4-hexyloxyphenol (21.7 g, 112 mmol), and potassium carbonate (19.3 g, 140 mmol) were added to NMP (1.0 L) under a nitrogen atmosphere. Then the mixture was heated to 120 °C for 12 h. After cooling to room temperature, the solution was poured into 1.0 N HCl (580 mL), the precipitate was collected by filtration, and the residue was washed with water. Finally, the crude residue was purified by recrystallization using ethyl acetate, and compound 2 (19.9 g, 15.0 mmol, 54%) as a purple solid was obtained. 1H NMR (400 MHz, CDCl3): δ (ppm) 8.06 (s, 4H), 6.89 (m, 8H), 6.80 (m, 8H), 4.92 (m, 2H), 3.93 (t, J = 6.6 Hz, 8H), 2.44 (m, 4H), 1.85 (m, 8H), 1.78 (m, 8H), 1.66 (m, 8H), 1.48 (m, 8H), 1.37 (m, 16H), 0.93 (m, 12H). 13C NMR (100 MHz, CDCl3): δ (ppm) 167.7, 163.8, 156.6, 156.1, 148.4, 130.8, 128.8, 121.4, 119.6, 118.8, 115.7, 68.5, 53.9, 38.7, 31.6, 29.3, 29.1, 26.5, 25.7, 22.6, 14.1. MALDITOF MS: 1324 ([M + 1H]+). Synthesis of Compound 3. Compound 2 (19.9 g, 15.0 mmol) and potassium hydroxide (71.6 g, 1.28 mol) were solved

tives have yet to be reported. The examination of fundamental electron-transfer properties such as reorganization energy62−64 is therefore important for the applicative research for energy conversion and organic electronic devices.65−67 In this work, two different coroneneimide derivatives were employed as electron acceptors, taking the difference between five- and six-membered imide groups (namely, Cor(5Im)2, and Cor(6Im)2 in Chart 1) into consideration, to examine the intermolecular68−72 and intramolecular73−78 photoinduced electron-transfer properties. Regarding the intermolecular photoinduced electron transfer, by utilizing various electron donor molecules (D) with different one-electron oxidation potentials,79 the rate constants of intermolecular electron transfer from D to the triplet excited states of coronendiimide [3Cor(5Im)2* or 3Cor(6Im)2*] were determined by nanosecond transient absorption measurements. The reorganization energies (λ) of Cor(5Im)2 and Cor(6Im)2 were determined from the deriving force (−ΔGet) dependence of the rate constants of electron transfer. In addition, a new covalently linked donor (perylene)−acceptor dyad (Chart 1) [denoted as Cor(5Im)2−Pery] was synthesized to investigate the dynamics of ultrafast intramolecular PET between Cor(5Im)2 and Pery. A perylene derivative was chosen as an electron donor moiety due to the one-electron oxidation potential (Eox = 1.04 V vs SCE)80 and the simple synthetic introduction of substituents onto the perylene core for improved solubility.81−83 The spectroscopic, electrochemical, and photophysical properties of Cor(5Im)2− Pery were examined by steady-state and time-resolved spectroscopies, electrochemical methods, and electron spin resonance (ESR) spectroscopies.



EXPERIMENTAL METHOD General Information. All solvents and reagents were purchased from Tokyo Chemical Industry, Kanto Chemical Co., Inc., Nacalai Tesque, and Wako Pure Chemical Industries. All commercial reagents were used without further purification. Column flash chromatography was performed on silica gel (Kanto Chemical Silica gel 60N, 40−50 or 100−210 μm). B

DOI: 10.1021/acs.jpcc.7b09817 J. Phys. Chem. C XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry C

NMR (400 MHz, CDCl3): δ (ppm): 7.63 (d, J = 9.4 Hz, 1H), 7.57 (d, J = 8.8 Hz, 2H), 7.52 (d, J = 8.2 Hz, 2H), 7.38 (d, J = 8.2 Hz, 2H), 7.21 (s, 1H), 7.03 (d, J = 8.8 Hz, 2H), 6.95 (d, J = 9.4 Hz, 1H), 6.94 (s, 1H), 6.84 (m, 8H), 6.73 (m, 8H), 3.88 (m, 8H), 2.19 (s, 3H), 1.75 (m, 8H), 1.45 (m, 8H), 1.34 (m, 16H), 0.92 (m, 12H). 13C NMR (100 MHz, CDCl3): δ (ppm) 168.2, 155.0, 154.4, 154.3, 154.2, 153.8, 152.1, 152.0, 151.8, 151.6, 150.2, 150.2, 150.1, 150.0, 139.0, 137.1, 136.1, 135.2, 132.1, 132.1, 132.0, 130.5, 128.8, 128.6, 127.0, 125.5, 124.8, 123.1, 120.9, 120.9, 120.8, 120.8, 119.7, 117.9, 117.8, 117.0, 116.9, 116.9, 116.7, 116.0, 115.9, 115.8, 115.1, 68.5, 31.6, 29.3, 25.7, 24.7, 22.6, 14.0. MALDI-TOF MS: 1154 (M). Synthesis of Compound 6. Pery (5.41 g, 4.69 mmol) was solved into ethanol (1.4 L). Then concentrated HCl (950 mL) was added dropwise to the solution, and the mixture was refluxed for 12 h. After cooling to 0 °C, 1.0 M NaOH aqueous solution (10 mL) was added dropwise to the mixture. Then, compound 6 was extracted with chloroform. The organic layer was washed with water and brine and dried over anhydrous MgSO4. After evaporation of organic solvent, the crude residue was purified by column chromatography on silica gel eluting with chloroform/toluene (30/1, v/v), and compound 6 (4.69 g, 4.22 mmol, 90%) was obtained as a brown solid. 1H NMR (400 MHz, CDCl3): δ (ppm) 7.70 (d, J = 9.4 Hz, 1H), 7.56 (dd, J = 9.2, 2.4 Hz, 2H), 7.22 (d, J = 9.0 Hz, 2H), 7.02 (dd, J = 9.2, 2.4 Hz, 2H), 6.95 (s, 1H), 6.94 (d, J = 9.4 Hz, 1H), 6.84 (m, 8H), 6.73 (m, 8H), 6.71 (d, J = 9.0 Hz, 2H), 3.88 (m, 8H), 3.73 (s, 2H) 1.75 (m, 8H), 1.45 (m, 8H), 1.34 (m, 16H), 0.91 (m, 12H). 13C NMR (100 MHz, CDCl3): δ (ppm) 154.9, 154.9, 154.8, 154.1, 154.1, 154.0, 153.8, 150.2, 150.2, 150.1, 145.8, 139.9, 136.0, 135.1, 130.8, 130.1, 126.8, 126.7, 125.8, 124.8, 123.4, 120.9, 120.8, 120.8, 117.7, 117.0, 116.9, 116.5, 116.0, 116.0, 115.8, 115.1, 114.9, 114.7, 68.4, 31.6, 29.3, 25.7, 22.6, 14.0. MALDI-TOF MS: 1111 (M). Synthesis of Cor(5Im)2−Pery. Compound 6 (0.244 g, 0.211 mmol), compound 7 (0.583 g), and zinc acetate (0.038 g, 0.211 mmol) were solved into quinoline (21 mL), and the solution was stirred at 180 °C for 2.5 days. After cooling to 0 °C, 1.0 N HCl (68 mL) was added into the solution. Then the suspension was filtered, and the residue was washed with water and methanol. The collected solid was resolved in hexane/ethyl acetate/toluene (10/2/1, v/v/v) and filtered through Celite. The solid was purified by column chromatography on silica gel eluting with hexane/ethyl acetate/toluene (10/2/1, v/v/v), followed by toluene/hexane/ethyl acetate (10/10/1, v/v/v). Preparative recycling gel permeation chromatography (chloroform) and preparative thin layer chromatography (toluene/ hexane = 7/1) were performed for further purification. Finally, Cor(5Im)2−Pery dyad (0.0019 g, 0.0012 mmol, 0.5%) was obtained as a brown solid. 1H NMR (400 MHz, CDCl3): δ (ppm) 10.16 (d, J = 9.0 Hz, 2H), 10.09 (d, J = 9.0 Hz, 2H), 9.06 (d, J = 10.2 Hz, 2H), 9.02 (d, J = 10.2 Hz, 2H), 7.85 (d, J = 9.2 Hz, 1H), 7.84 (d, J = 8.8 Hz, 2H), 7.76 (d, J = 8.8 Hz, 2H), 7.61 (d, J = 9.2 Hz, 2H), 7.12 (s, 1H), 7.07 (d, J = 9.2 Hz, 2H), 7.06 (d, J = 9.2 Hz, 1H), 6.90 (m, 8H), 6.78 (m, 8H), 4.61 (m, 1H), 3.92 (m, 8H), 2.40 (m, 2H), 1.92 (m, 2H), 1.78 (m, 12H), 1.47 (m, 8H), 1.35 (m, 16H), 1.04 (t, J = 7.6 Hz, 6H), 0.92 (m, 12H). 13C NMR (100 MHz, CDCl3): δ (ppm) 167.8, 155.0, 154.6, 154.3, 152.9, 152.7, 151.8, 150.8, 150.2, 149.9, 148.9, 138.9, 138.4, 136.0, 134.7, 132.4, 130.9, 128.8, 128.1, 127.7, 127.3, 127.0, 126.8, 125.6, 124.8, 124.2, 123.8, 123.2, 122.6, 122.3, 121.0, 120.2, 119.8, 119.1, 118.5, 118.1, 116.3, 115.9, 114.8, 112.8, 112.1, 111.6, 68.2, 50.9, 38.7, 30.4, 29.7,

into 2-propanol (665 mL), and the solution was refluxed for 12 h. After cooling to room temperature, the mixture was poured into acetic acid (2.0 L) and stirred at room temperature for 24 h. The precipitation was collected by filtration. Finally, the crude residue was purified by recrystallization using ethyl acetate, and compound 3 (11.9 g, 10.2 mmol, 68%) as a purple solid was obtained. 1H NMR (400 MHz, CDCl3): δ (ppm) 8.09 (s, 4H), 6.90 (m, 8H), 6.84 (m, 8H), 3.94 (t, J = 6.8 Hz, 8H), 1.80 (m, 8H), 1.49 (m, 8H), 1.37 (m, 16H), 0.93 (t, J = 6.8 Hz, 12H). Synthesis of Compound 4. Compound 3 (11.9 g, 10.2 mmol), copper(I) oxide (8.26 g, 57.7 mmol), and copper powder (0.826 g, 13.0 mmol) added into quinoline (580 mL), and the mixture was stirred at 220 °C for 12 h. The half-volume of solvent was evaporated under reduced pressure and the solution was poured into a stirred mixture of 1.0 N HCl (2.0 L). Next, the yellow precipitate was collected by filtration and washed with water. Finally, the crude residue was purified by column chromatography on silica gel eluting with dichloromethane/hexane (2/1, v/v), and compound 4 (9.24 g, 9.05 mmol, 89%) was obtained as a purple solid. 1H NMR (400 MHz, CDCl3): δ (ppm) 7.56 (d, J = 8.8 Hz, 4H), 7.01 (d, J = 8.8 Hz, 4H), 6.83 (m, 8H), 6.74 (m, 8H), 3.89 (t, J = 6.6 Hz, 8H), 1.76 (m, 8H), 1.45 (m, 8H), 1.35 (m, 16H), and 0.92 (t, J = 6.8 Hz, 12H). 13C NMR (100 MHz, CDCl3): δ (ppm): 154.9, 154.2, 150.2, 135.2, 127.0, 124.9, 120.8, 117.0, 115.9, 115.1, 68.5, 31.6, 29.3, 25.7, 22.6, 14.0. MALDI-TOF MS: 1021 ([M + 1H]+). Synthesis of Compound 5. Compound 4 (9.24 g, 9.05 mmol) was solved into DMF (300 mL), and the mixture was protected from light. Next, NBS (1.61 g, 9.05 mmol) was added into the solution little by little at 0 °C and the mixture was stirred at 70 °C for 24 h. After cooling to room temperature, the solution was poured into 1.0 N HCl (66 mL), and the compound 5 was extracted with ethyl acetate. The organic layer was washed with water and brine and dried over anhydrous MgSO4. After evaporation of organic solvent, the crude residue was purified by column chromatography on silica gel eluting with dichloromethane/hexane (1/2, v/v), and compound 5 (7.47 g, 6.79 mmol, 75%) was obtained as a brownish yellow solid. 1H NMR (400 MHz, CDCl3): δ (ppm): 7.91 (d, J = 9.2 Hz, 1H), 7.58 (d, J = 9.2 Hz, 2H), 7.30 (s, 1H), 7.09 (d, J = 9.2 Hz, 1H), 7.02 (d, J = 9.2 Hz, 1H), 7.01 (d, J = 9.2 Hz, 1H), 6.82 (m, 8H), 6.76 (m, 8H), 3.89 (m, 8H), 1.76 (m, 8H), 1.46 (m, 8H), 1.35 (m, 16H), 0.92 (t, J = 6.4 Hz, 12H). 13C NMR (100 MHz, CDCl3): δ (ppm) 155.2, 155.1, 155.0, 155.0, 154.7, 154.5, 154.4, 153.5, 149.8, 149.8, 149.6, 149.5, 135.9, 134.6, 127.3, 127.3, 126.3, 124.5, 123.5, 121.2, 121.0, 120.9, 120.9, 120.9, 117.5, 116.7, 116.7, 115.8, 115.2, 115.2, 115.0, 68.3, 31.6, 29.2, 25.7, 22.6, 14.0. MALDI-TOF MS: 1103 ([M + 3H]3+). Synthesis of Pery. Compound 5 (7.47 g, 6.79 mmol) and potassium bicarbonate (3.76 g, 27.2 mmol), 4′-(4,4,5,5tetramethyl-1,3,2-dioxaborolan-2-yl) acetanilide (2.66 g, 10.2 mmol), and palladium(0)tetrakis(triphenylphosphine) (0.314 g, 0.272 mmol) were added into the mixture solution of toluene (375 mL), ethanol (15 mL), and water (15 mL), and the solution was stirred at 95 °C for 20 h. After cooling to room temperature, Pery was extracted with chloroform. The organic layer was washed with water and brine and dried over anhydrous MgSO4. After evaporation of organic solvent, the crude residue was purified by column chromatography on silica gel eluting with chloroform/toluene (30/1, v/v), and Pery (5.41 g, 4.69 mmol, 69%) was obtained as a brown solid. 1H C

DOI: 10.1021/acs.jpcc.7b09817 J. Phys. Chem. C XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry C Scheme 1. Synthetic Scheme of Cor(5Im)2−Pery

28.9, 23.7, 23.0, 14.1, 11.0. MALDI-TOF MS: 1632 ([M + 1H]+).



Compound 1 was synthesized as previously reported method84,85 using 3,4,9,10-perylenetetracarboxylic dianhydride as a starting compound. The four chlorine atoms in compound 1 were substituted by aryl groups under basic conditions to afford compound 2. Hydrolysis of compound 2 using potassium hydroxide and subsequent decarboxylation catalyzed by copper and copper(I) oxide gave compound 4. Compound 4 was reacted with N-bromosuccinimide (NBS) to synthesize compound 5. The Suzuki−Miyaura coupling reaction between compound 5 and acetamidophenylboron derivative produced Pery. To afford compound 6, Pery was performed to deacetylation under acidic condition. Finally, Cor(5Im)2− Pery was obtained by dehydration between compound 6 and

RESULTS AND DISCUSSION

Synthesis. Cor(5Im)2 and Cor(6Im)2 were synthesized as previously reported.59 The synthesis of Cor(5Im)2 was achieved by using Diels−Alder reaction as a key reaction, whereas Cor(6Im)2 was synthesized by using Sonogashira coupling reaction. Cor(5Im)2−Pery was also synthesized on the basis of previous studies (Scheme 1).84−89 To improve the solubility, aryl groups were introduced onto the perylene core and 4-heptyl groups were substituted onto the imide units. D

DOI: 10.1021/acs.jpcc.7b09817 J. Phys. Chem. C XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry C

Concerning the fluorescence spectra (Figure 1B), a similar spectral trend was observed. The sharp and split peaks of Cor were observed at 428, 447, 455, 475, 485, and 508 nm (spectrum a), whereas the spectra of Cor(5Im)2 and Cor(6Im)2 became broadened and red-shifted (spectra b and c). On the basis of the above results, the excitation energies of Cor(5Im)2 and Cor(6Im)2 derived from 0 to 0 transition were estimated to be 2.54 and 2.40 eV, respectively. Additionally, the phosphorescence spectra of Cor(5Im)2 and Cor(6Im)2 in frozen 2methyl THF were already measured as reported by us previously.59 The corresponding triplet energies were 2.03 eV for Cor(5Im)2 and 2.04 eV for Cor(6Im)2.59 Steady-State Spectroscopic Measurements of Cor(5Im)2−Pery Dyad. The steady-state absorption and fluorescence spectra of Cor(5Im)2−Per were obtained in PhCN as shown in Figures 2A and 2B, respectively. In Figure 2A, the

compound 7 (precursor of Cor(5Im)2). The details of synthetic procedures are given in the Experimental Method. 1H NMR spectroscopy, 13C NMR spectroscopy, and MALDI-TOF-MS are shown in Figures S1−S18 in the Supporting Information. Steady-State Spectroscopic Measurements of Coronenediimides. The steady-state spectroscopic measurements were performed to examine the electronic structures of coroneneimide derivatives. Figure 1A shows absorption spectra

Figure 1. (A) Absorption and (B) fluorescence emission spectra of (a) coronene (black), (b) Cor(5Im)2 (red), and (c) Cor(6Im)2 (blue) measured in PhCN (20 μM). Excitation wavelength: 343 nm for coronene and 435 nm for Cor(5Im)2 and Cor(6Im)2.

of pristine coronene (Cor), Cor(5Im)2, and Cor(6Im)2 in benzonitrile (PhCN). The absorption spectrum of Cor (spectrum a) has characteristic strong peaks at 307, 327, and 343 nm. The weak absorption peaks of Cor at 389, 411, and 428 nm are assigned to symmetry-forbidden transitions. In the case of Cor(5Im)2 and Cor(6Im)2 (spectra b and c), the peaks became remarkably broadened and red-shifted as compared to those of Cor, together with the appearance of new peaks in the 400−500 nm region. According to the results of DFT calculations (Table 1 and SI Figure S19), a possible reason for the red shift is the significant lowering of the lowest unoccupied molecular orbital (LUMO) energy levels as compared to that of the highest occupied molecular orbital (HOMO) energy levels by introducing imide groups, which leads to the decrease in the HOMO−LUMO gap.

Figure 2. (A) Absorption spectra of (a) Cor(5Im)2−Pery (black), (b) Pery (blue), and (c) Cor(5Im)2 (red) measured in PhCN. (B) Fluorescence emission spectra of (a) Cor(5Im)2−Pery (black) and (b) Pery (blue) measured in PhCN. (20 μM). Excitation wavelength: 435 nm.

respective peaks of Cor(5Im)2 and Pery units can be identified in the spectrum of Cor(5Im)2−Pery by comparing the corresponding reference monomers, although the peaks of Cor(5Im)2−Pery are relatively broadened. For example, in the 400−500 nm region, two broad peaks derived from Pery unit at 437 and 461 nm were observed, whereas the additional peak at

Table 1. Summarized Redox Potentials and Energy Levels of Cor(5Im)2, Cor(6Im)2, Pery, and Cor(5Im)2−Pery

a

compound

Ered1a

Ered2a

Cor(5Im)2 Cor(6Im)2 Pery Cor(5Im)2−Pery

−1.05 −0.79

−1.40 −1.08

−1.03

−1.34

Eox1a

0.72 0.67

Eox2a

HOMO,b eV

LUMO,b eV

1.04 1.09

−6.04 −6.20 −4.43 −4.53

−2.85 −3.02 −1.51 −2.93

V vs SCE. bCalculated at the B3LYP/6-31G(d) level of theory. E

DOI: 10.1021/acs.jpcc.7b09817 J. Phys. Chem. C XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry C 488 nm was attributable to Cor(5Im)2. Steady-state fluorescence spectra of Cor(5Im)2−Pery and Pery with the excitation at 435 nm are shown in Figure 2B. This excitation wavelength corresponds to the absorption maximum of Pery (437 nm). Then, we fixed the same absorbance for the excitation wavelength (435 nm) to compare the quenching efficiencies between Cor(5Im)2−Pery and Pery. The fluorescence spectrum of Pery with excitation at 435 nm (spectrum a in Figure 2A) shows a peak at 496 nm. In contrast, the emission of Cor(5Im)2−Pery is strongly quenched (>99%; see spectrum b). These results suggest an additional deactivation pathway from the excited state of the perylene units that arises from the interaction between Pery and Cor(5Im)2 units in Cor(5Im)2−Pery. This quenching in Cor(5Im)2−Pery presumably result from intramolecular photoinduced electron transfer from the singlet excited state of Pery to Cor(5Im)2 (vide inf ra). Electrochemical Measurements. The electrochemical behaviors of coroneneimide and perylene derivatives were investigated by cyclic voltammetry. The measurements were performed in PhCN containing 0.1 M of nBu4NPF6 as a supporting electrolyte with a sweep rate of 0.1 V s−1. Typical examples are shown in Figure 3. The measured half-wave

Cor(5Im)2−Pery also exhibited reversible redox waves that correspond to the first one-electron oxidation (Pery•+/Pery) and reduction (Cor(5Im)2/Cor(5Im)2•−) processes. The first one-electron reduction (Ered1) and oxidation (Eox1) potentials were assigned to be −1.03 and +0.67 V vs SCE, respectively (Figure 3d). These values are very similar to those of single reference components, i.e., Ered1 of Cor(5Im)2 (−1.05 V) and Eox1 of Pery (0.72 V), as shown in Table 1. These electrochemical results indicate that Cor(5Im)2 and Pery units are successfully identified in the Cor(5Im)2−Pery dyad. Considering the above electrochemical data, the energy level of the charge-separated state of Cor(5Im)2−Pery (namely, Cor(5Im)2•−−Pery•+) was determined to be 1.70 eV from the difference between Eox1 of Pery and Ered1 of Cor(5Im)2. This value is much smaller than the excited energies of each chromophore: 2.54 eV for 1Pery* and 2.58 eV for 1Cor(5Im)2*. Spectroelectrochemical Characterization of Reduced Coronenediimides. The radical anions of Cor(5Im)2 and Cor(6Im)2 were produced by the electron-transfer reduction by the naphthalene radical anion, which was prepared by reduction of naphthalene with sodium metal in Ar-saturated THF. Parts A and B of Figure 4 show the absorption spectral changes

Figure 3. Cyclic voltammograms of (a) Cor(5Im)2 (red), (b) Cor(6Im)2 (green), (c) Pery (blue), and (d) Cor(5Im)2−Pery (black) in PhCN (0.1 mM) with 0.1 M nBu4NPF6 as a supporting electrolyte. Scan rate: 0.1 V s−1.

potentials of these compounds are summarized in Table 1. The first one-electron reduction potential (Ered1) values of Cor(5Im)2 and Cor(6Im)2 were assigned to be −1.05 and −0.79 V vs SCE, respectively. Upon comparison of the Ered1 values with that of pristine coronene (−2.02 V vs SCE) reported in the previous paper,59 the positive shift of reduction potentials is clearly observed by introduction of electron-withdrawing imide groups. In other words, an increased trend of the electronaccepting property is observed in the coroneneimide derivatives. According to the results of DFT calculations (Supporting Information Figure S19), the LUMOs of Cor(5Im)2 and Cor(6Im)2 expand to the substituted-imide units. Therefore, carbonyl groups in the imide unit probably contribute to the stabilization of the radical anion states. Additionally, using the values of Ered1 (Table 1) and the triplet excited energies (Cor(5Im)2, 2.03 eV; Cor(6Im)2, 2.04 eV),44 the one-electron reduction potentials of 3Cor(5Im)2* and 3 Cor(6Im)2* were determined to be 0.98 and 1.25 V vs SCE, respectively.

Figure 4. vis−NIR spectral changes observed in chemical electrontransfer reduction of (A) Cor(5Im)2 and (B) Cor(6Im)2 by naphthalene radical anion in Ar-saturated THF at 298 K.

resulting from the electron-transfer reduction of Cor(5Im)2 to Cor(5Im)2•− and Cor(6Im)2 to Cor(6Im)2•−. The spectra have broadened absorption ranges from 500 nm to NIR as compared to those of the pristine Cor(5Im)2 and Cor(6Im)2. The molar absorption coefficients of Cor(5Im)2•− (5.2 × 103 M−1 cm−1 at 525 nm, 6.0 × 103 M−1 cm−1 at 556 nm, and 7.7 × 102 M−1 cm−1 at 731 nm) and Cor(6Im)2•− (1.4 × 104 M−1 cm−1 at 593 nm, 2.0 × 103 M−1 cm−1 at 897 nm, and 4.9 × 103 M−1 cm−1 at 1008 nm) were determined from the measurements. Electron Spin Resonance (ESR) Spectra of Radical Anions of Coronenediimides. Using dimeric 1-benzyl-1,4F

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Figure 5. ESR spectra of radical anions of (A) Cor(5Im)2 and (B) Cor(6Im)2 generated by photoinduced electron-transfer reduction of Cor(5Im)2 and Cor(6Im)2 with (BNA)2 at 298 K (top panel). Simulated spectra obtained using best-fit hyperfine coupling constants (hfc) given as the experimental values in the inserted tables, where the hfc values obtained by DFT calculations of the corresponding radical anions at the M06-2X/6311+G(d,p) level of theory are given for comparison (middle panel). Spin density maps of radical anions (lower panel).

Intermolecular Photoinduced Electron-Transfer Reduction of Coronenediimides. Nanosecond laser-induced transient absorption measurements of Cor(6Im)2 were performed in the presence of different electron donor molecules in PhCN at 298 K to elucidate the dynamics of electron-transfer reduction of 3Cor(6Im)2*. As discussed above, the one-electron reduction potential of 3Cor(6Im)2* was estimated to be 1.25 V vs SCE from Ered1 of Cor(6Im)2 (−0.79 V vs SCE) and the corresponding triplet energy (2.04 eV). Similarly, the one-electron reduction potential of 3Cor(5Im)2* was calculated to be 0.98 V vs SCE. Because the oneelectron oxidation potential of Pery (Eox1 = 0.72 V vs SCE) is lower than the one-electron reduction potential of 3Cor(6Im)2*, the deriving force of electron transfer from Pery to 3 Cor(6Im)2* is positive (−ΔGet = 0.53 eV) when the electron transfer is energetically favorable. The driving force of back electron transfer from Cor(6Im)2•− to Pery•+ is also largely positive (−ΔGbet = 1.86 eV). The occurrence of photoinduced electron transfer was confirmed by the appearance of a new peak due to Cor(6Im)2•−, accompanied by the decay of the T−T absorption of 3Cor(6Im)2* (Figure 7A). At 15 μs after the laser excitation at 355 nm, a broad peak around 550−750 nm due to the T−T absorption of 3Cor(6Im)2* was observed. The decay of the absorbance at 590 nm coincided with the rise in the absorbance at 1010 nm due to Cor(6Im)2•−, indicating the occurrence of the electron-transfer reaction. The decay of the absorbance at 1010 nm (at 200 μs) results from the back electron-transfer reaction. The decay rate constant of the T−T absorption at 710 nm due to of 3Cor(6Im) 2* increased with the increasing

dihydronicotinamide [(BNA)2] as an electron donor, oneelectron reductions of Cor(5Im)2 and Cor(6Im)2 were achieved by irradiation of visible light to a CH2Cl2 solution containing (BNA)2 and Cor(5Im)2 (or Cor(6Im)2) at 298 K. Photoinduced electron transfer from (BNA)2 to Cor(5Im)2 and Cor(6Im)2 resulted in formation of Cor(5Im)2•− and Cor(6Im)2•−, respectively. The ESR spectra of Cor(5Im)2•− and Cor(6Im)2•− are shown in Figures 5A and 5B (top panel), respectively. To analyze the spectra, the assignments of hfc values were carried out by DFT calculations of the corresponding radical anions at the M06-2X/6-311+G(d,p) level of theory. The optimized structures are shown with the spin distributions in Figure 5 (lower panel). The observed spectra are well-fitted by the computer simulation as shown in Figure 5 (middle panels) using the hfc values, which agree with those obtained by DFT calculations (inserted Tables in Figure 5). The ESR spectra clearly show the hyperfine splitting due to aromatic hydrogens (Ha and Hb) shown and two nitrogens, revealing that the unpaired electrons are fully delocalized on the aromatic part of coronenediimides. Triplet−Triplet Absorption of Coronenediimides. The triplet−triplet (T−T) absorption spectra of Cor(5Im)2 and Cor(6Im)2 in deaerated PhCN were measured by nanosecond laser flash photolysis as shown in Figures 6A and 6B, where the initial spectra were taken at 2 μs after laser excitation. The decay of the absorbance at 430 nm due to 3Cor(5Im)2* and 570 nm due to 3Cor(6Im)2* obeyed the first-order kinetics. The lifetime (τT) of 3Cor(5Im)2* and 3Cor(6Im)2* at 298 K were determined to be 91 and 40 μs, respectively. It should be noted that there is no significant contribution of T−T annihilation under the presented laser excitation conditions. G

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wp is the electrostatic interaction energy in the radical ion pair, which corresponds to the work term required to bring the product radical ions to their mean separation in the radical ion pair for the intermolecular electron transfer. Note that the wp was neglected in this analysis because of the large static dielectric constant of benzonitrile and delocalized charges in the radical ion pair. The obtained ket and kbet values, together with the driving force of electron transfer (−ΔGet) or back electron transfer (−ΔGbet) are summarized in Table 2. Donor molecules employed in the measurements are 2-methylindole (2MI) (Eox1 = 1.07 V vs SCE),91 triethylamine (TEA) (Eox1 = 0.96 V vs SCE),92 triphenylamine (TPA) (Eox1 = 0.86 V vs SCE),92 and dimethoxyaniline (DMA) (Eox1 = 0.81 V vs SCE).93 Note that these donor molecules have no absorption at 355 nm and we can selectively excite Cor(5Im)2 or Cor(6Im)2. In both cases of Cor(5Im)2 and Cor(6Im)2, the ket values monotonously increase with increments in the driving force (−ΔGet) to approach the plateau value of the diffusion-limited region. However, the ket values of electron transfer from electron donors to 3Cor(5Im)2* are significantly larger than that to 3Cor(6Im)2* when the ket values less than the diffusionlimit values are compared at the similar driving force of electron transfer (−ΔGet). For example, the ket value from DMA to 3 Cor(5Im)2* (1.2 × 109 M−1 s−1; −ΔGet = 0.17 eV) is 18-fold larger than that from 2MI to 3Cor(6Im)2* (6.5 × 107 M−1 s−1; −ΔGet = 0.18 eV). This result implies the difference in the electron-transfer reduction properties between Cor(5Im)2 and Cor(6Im)2. On the contrary, all the kbet values examined in this study are in the diffusion limit region. The plots of log ket vs −ΔGet for Cor(5Im)2 and Cor(6Im)2 are shown in Figure 8. Because the Marcus theory of electrontransfer states that the activation free energy of electron transfer (ΔG*) is expressed as eq 2, the observed rate constants of intermolecular electron transfer (ket) follow the eq 3:69

Figure 6. (A) Nanosecond transient absorption spectra of Cor(5Im)2 (100 μM) in Ar-saturated PhCN taken at 2.0 μs (black), 100 μs (red), and 200 μs (blue) after laser excitation at 355 nm (inset: time profile of absorbance at 430 nm). (B) Nanosecond transient absorption spectra of Cor(6Im)2 (25 μM) in Ar-saturated PhCN taken at 2.0 μs (black), 50 μs (red), and 150 μs (blue) after laser excitation at 355 nm (inset: time profile of absorbance at 570 nm). Excitation wavelength: 355 nm.

concentration of Pery (Figure 7B). Figure 7C shows a linear plot of the observed decay rate constant (kobs) at 710 nm vs concentration of Pery. From the slope of the linear plot, the second-order rate constant of electron transfer from Pery to 3 Cor(6Im)2* was determined to be 2.1 × 109 M−1 s−1. This value is close to the diffusion limited value in PhCN (5.6 × 109 M−1 s−1).90 The decay of the absorption band at 1010 nm due to Cor(6Im)2•− obeyed the second-order kinetics due to the bimolecular reaction (Figure 7D). The second-order plot (inset of Figure 7D) for the decay of Cor(6Im)2•− was obtained from the absorbance at 1010 nm and the molar absorption coefficient of Cor(6Im)2•− determined by the electron-transfer reduction of Cor(6Im)2 with the naphthalene radical anion (4.9 × 103 M−1 cm−1 at 1008 nm). From the slope of the linear plot, the second-order rate constant of the back electron transfer from Cor(6Im)2•− to Pery•+ was determined to be 4.0 × 109 M−1 s−1. This value is also close to the diffusion-limited value in PhCN (5.6 × 109 M−1 s−1).90 The ket and kbet values of electron transfer from various electron donors to 3Cor(5Im)2* or 3Cor(6Im)2* were determined in the same manner (transient absorption spectra, pseudo-first-order plots, and second-order plots are shown in Supporting Information Figures S20−S46). The driving force of electron transfer from electron donors to electron acceptors (Cor(5Im)2 or Cor(6Im)2) can be obtained by using eq 1: ΔGet = e[E°(D+ /D) − E°(A/A−)] + wp

ΔG* =

λ(1 + ΔGet /λ)2 4

(2)

1 1 1 = + ⎡ λ(1 + ΔGet / λ)2 ⎤ ket kdiff Z exp⎣⎢ ⎦⎥ 4kBT

(3)

where kdiff is the diffusion rate constant, Z is the collision frequency (chosen as 1 × 1011 M−1 s−1), λ is the reorganization energy, and kB is the Boltzmann constant. When the plots in Figure 8 were fit to eq 3, the reorganization energy of the electron-transfer reduction of Cor(5Im)2 and Cor(6Im)2 were determined to be 0.77 and 1.15 eV, respectively. The λ value of Cor(5Im)2 is as small as that of C60 (0.73 eV) in PhCN determined by the same procedure.69 The reorganization energy is composed of the sum of inner reorganization energy (λi) and solvent reorganization energy (λs), as expressed in eq 4:60 λ = λ i + λs

(4)

The reported theoretical values of λi obtained by DFT calculations at the M06-2X/6-311+G(d,p) level of theory are 0.29 eV for Cor(5Im)2 and 0.35 eV for Cor(6Im)2.60 The λi value of Cor(5Im)2 is slightly smaller than that of Cor(6Im)2. These calculation values suggest that the solvent reorganization is the major barrier of the electron-transfer reduction of Cor(5Im)2 and Cor(6Im)2 in PhCN. Additionally, the marginal difference in λi values indicates that the λs values contribute to the difference in the λ values. Additionally, charge density maps

(1) +

where e stands for the elementary charge, E°(D /D) and E°(A/ A−) are the oxidation potential of the electron donor and the reduction potential of the electron acceptor, respectively, and H

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Figure 7. (A) Transient absorption spectra of Cor(6Im)2 (77 μM) in the presence of Pery (12 μM) in Ar-saturated PhCN taken at 15 μs (black), 70 μs (red), and 200 μs (blue) after laser excitation at 355 nm at 298 K. (B) Time profiles of absorbance at 710 nm upon laser excitation to Cor(6Im)2 (77 μM) in the presence of different concentrations of Pery in PhCN. (C) Plots of the pseudo-first-order rate constant (kobs) vs the concentration of Pery. (D) Decay time profile of absorbance at 1010 nm due to back electron transfer from Cor(6Im)2•− to Pery•+ in PhCN containing Cor(6Im)2 (80 μM) and Pery (200 μM). Inset: The second-order plots.

Table 2. Rate Constants of Electron Transfer from Electron Donors to 3Cor(5Im)2* or 3Cor(6Im)2* and Back Electron Transfer in PhCN at 298 K acceptor

−ΔGet or − ΔGbet [eV]

Cor(5Im)2* Cor(5Im)2* 3 Cor(5Im)2* 3 Cor(5Im)2* 3 Cor(5Im)2* Pery•+ DMA•+ TPA•+ TEA•+ 2MI•+ 3 Cor(6Im)2* 3 Cor(6Im)2* 3 Cor(6Im)2* 3 Cor(6Im)2* 3 Cor(6Im)2* Pery•+ DMA•+ TPA•+ TEA•+ 2MI•+

−0.09 0.02 0.12 0.17 0.26 1.77 1.86 1.91 2.01 2.12 0.18 0.29 0.39 0.44 0.53 1.51 1.60 1.65 1.75 1.86

donor 2MI TEA TPA DMA Pery Cor(5Im)2•− Cor(5Im)2•− Cor(5Im)2•− Cor(5Im)2•− Cor(5Im)2•− 2MI TEA TPA DMA Pery Cor(6Im)2•− Cor(6Im)2•− Cor(6Im)2•− Cor(6Im)2•− Cor(6Im)2•−

3 3

ket or kbet [M−1 s−1] 7.2 2.1 2.7 1.2 2.4 5.5 2.2 5.6 2.8 2.4 6.5 1.1 4.9 1.5 2.1 4.0 5.6 4.2 2.6 1.1

× × × × × × × × × × × × × × × × × × × ×

106 108 108 109 109 109 109 109 109 109 107 108 108 109 109 109 109 109 109 109

Figure 8. Driving force dependence of log ket for electron transfer from electron donors to 3Cor(5Im)2* or 3Cor(6Im)2* in PhCN at 298 K. The fitting curves are obtained on the basis of eq 3.

smaller than that of Cor(6Im)2. This may be related to the smaller λs value of Cor(5Im)2. However, the difference in λs has yet to be quantitatively understood. Femtosecond Transient Spectroscopic Measurements of Cor(5Im)2−Pery Dyad. In contrast to the abovementioned intermolecular electron transfer from 3Cor(5Im)2* to Pery, the occurrence of intramolecular electron transfer between Pery and Cor(5Im)2 in Cor(5Im)2−Pery dyad was examined by femtosecond laser-induced transient absorption measurements. Cor(5Im)2 was chosen as an electron acceptor unit because the reorganization energy of Cor(5Im)2 is smaller than that of Cor(6Im)2.

of radical anions of Cor(5Im)2 and Cor(6Im)2 were evaluated (Supporting Information Figure S48). The atomic charge density on four carbonyl oxygens of Cor(5Im)2 is relatively I

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Figure 9. (A) Femtosecond transient absorption spectra of Cor(5Im)2 taken at 5.0 ps (black), 30 ps (red), 1000 ps (blue), 2000 ps (green), and 3000 ps (pink) after laser excitation and time profile of absorbance at 600 nm. (B) Femtosecond transient absorption spectra of Pery taken at 5.0 ps (black), 100 ps (red), 1500 ps (blue), and 3000 ps (green) after laser excitation and time profile of absorbance at 670 nm. (C) Femtosecond transient absorption spectra of Cor(5Im)2−Pery taken at 0.50 ps (black), 5.0 ps (red), 30 ps (blue), 100 ps (green), and 3000 ps (pink) after laser excitation at 393 nm and time profile of absorbance at 700 nm in Ar-saturated PhCN.

Cor(5Im)2−Pery in PhCN using a 393 nm laser pulse. Judging from the above-mentioned absorption spectra of Cor(5Im)2− Pery and corresponding monomers (Figure 2A), approximately 60% of absorption at 393 nm are attributable to the Pery unit in Cor(5Im)2−Pery. Therefore, we mainly excited the Pery unit in Cor(5Im)2−Pery. The transient absorption spectra of Cor(5Im)2−Pery immediately exhibited a broad S−S absorption of Pery in the 550−700 nm region after the laser pulse excitation (0.5 ps). Then, the new bands due to Cor(5Im)2•− appeared at 5 ps, being assigned by the above-mentioned spectroelectrochemical characterization (Figure 4). The time profile of

Parts A and B of Figure 9 show the femtosecond transient spectra of reference compounds: Cor(5Im)2 and Pery, respectively. The singlet−singlet (S−S) absorption of Cor(5Im)2 and Pery were observed at 5 ps after laser excitation. The decay of the absorbance at 600 nm due to 1Cor(5Im)2* (Figure 9A) and 670 nm due to 1Pery* (Figure 9B) obeyed the first-order kinetics. For example, the lifetime (τS) of 1Pery* at 298 K was determined to be 2.1 ns, which is approximately similar to the value evaluated by fluorescence lifetime measurement (∼3 ns) (Supporting Information Figure S49). Figure 9C also shows the femtosecond transient spectra of J

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constant of the electron transfer ket was determined to be 1.4 × 1012 s−1 by femtosecond transient absorption measurements. These results provide valuable information for fundamental and applicative studies utilizing coronene and PAH derivatives.

absorbance at 700 nm corresponds to the forward electrontransfer process and the rate constant (kET) is estimated to be 1.4 × 10 12 s −1. The absorption bands of Cor(5Im) 2•− monotonously decreased to the T−T absorption of Pery, which was observed at 100 ps. The observation of the T−T absorption spectrum of Pery indicates the triplet−triplet energy transfer from anthracene to Pery (Supporting Information Figure S47). The rate constant of back electron transfer of Cor(5Im)2•−−Pery•+ (kBET) was determined to be 3.4 × 1010 s−1. The photophysical process was summarized in Scheme 2. The triplet energy of Pery (3Pery*: 1.57 V) was already



ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.7b09817. Experimental section, 1H, 13C NMR, and MALDI-TOF MS spectra, molecular orbitals estimated by DFT calculations, nanosecond transient absorption spectra, time profiles of absorbance, charge density map, and fluorescence lifetime profile (PDF)

Scheme 2. Summarized Excited-State Dynamics of the Cor(5Im)2−Pery Dyad



AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (T.H.). *E-mail: [email protected] (S.F.). ORCID

Shunichi Fukuzumi: 0000-0002-3559-4107 Taku Hasobe: 0000-0002-4728-9767 Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

reported.94,95 After laser-pulse excitation, photoinduced electron-transfer (PET) process between Pery and Cor(5Im)2 mainly proceeds to form the charge-separated state (Cor(5Im)2•−−Pery•+) because the rate constants of the corresponding intersystem crossing (ISC) processes are much smaller than that of PET. Consequently, the triplet state of Pery is generated and quenched via the singlet charge-separated state: 1(Cor(5Im)2•−−Pery•+), but not via the conventional ISC process. This is a possible reason for much shorter lifetime of Pery triplet state in Cor(5Im)2−Pery as compared to the conventional ISC pathway.

Notes

The authors declare no competing financial interest.



ACKNOWLEDGMENTS This work was partially supported by JSPS KAKENHI Grant Numbers No. 26286017, 16K14067, 17H05270, and 17H05162 to T.H., JP17H03010, JP16K13964 26288037, and 26620154 to K.O., JP16H02268 to S.F., and No. 17K14476 to H.S.





CONCLUSION In this study, the spectroscopic and electron-transfer reduction properties of Cor(5Im)2 and Cor(6Im)2 were examined through steady-state absorption, emission, transient absorption, and electrochemical measurements. In steady-state absorption spectral measurements, Cor(5Im)2 and Cor(6Im)2 show broadened and red-shifted spectra as compared to Cor, together with new peaks in the 400−500 nm region. The broadened and red-shifted trends are also observed in fluorescence measurements. These results are consistent with the results of electrochemical measurements and DFT calculations. The intermolecular electron transfer from various electron donors to 3Cor(5Im)2* or 3Cor(6Im)2* were examined to determine the reorganization energies (λ) of the electron-transfer reduction to be 0.77 eV for Cor(5Im)2 and 1.15 eV for Cor(6Im)2. Because the inner reorganization energies (λi) of Cor(5Im)2 and Cor(6Im)2 obtained by DFT calculations are almost identical, the difference in the solvent reorganization energies (λs) is the main contributory factor for the difference in the λ values between Cor(5Im)2 and Cor(6Im)2 in PhCN. On the contrary, ultrafast photoinduced intramolecular electron transfer was observed in a newly synthesized donor−acceptor dyad, Cor(5Im)2−Pery. The rate

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