Article Cite This: J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
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Hexa-peri-hexabenzo[7]helicene: Homogeneously π‑Extended Helicene as a Primary Substructure of Helically Twisted Chiral Graphenes Yusuke Nakakuki,† Takashi Hirose,*,† Hikaru Sotome,‡ Hiroshi Miyasaka,‡ and Kenji Matsuda*,† †
Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan ‡ Division of Frontier Materials Science and Center for Promotion of Advanced Interdisciplinary Research, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan S Supporting Information *
ABSTRACT: Helically twisted graphenes can be considered as a promising candidate for the nanometer-sized molecular inductors in molecular electronics and molecular spring materials in nanomechanics. Here, we report the synthesis of hexa-peri-hexabenzo[7]helicene, which represents a primary substructure of the helical graphenes. The helically twisted polycyclic aromatic hydrocarbon was synthesized by a tetrasubstituted alkene formation using McMurry coupling followed by stepwise photocyclodehydrogenation and aromatization reactions. The π-extended helicoid structure with a noticeable intramolecular π−π interaction was unambiguously determined by X-ray crystallography. The primary helical nanographene molecule has a small HOMO−LUMO band gap evidenced by the absorption edge that appeared at ca. 800 nm, which exhibits an excellent chiroptical property with a dissymmetry factor of circular dichroism of |gCD| = 0.016 at 680 nm. The femtosecond transient absorption spectroscopy revealed the ultrafast excited-state dynamics of the helical nanographene molecule, with a lifetime of only few picoseconds in the lowestenergy excited (S1) state.
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INTRODUCTION Ortho-fused polycyclic aromatic compounds, named helicenes,1,2 have been attracting attention not only for the development of synthetic methods toward aromatic molecules with highly strained structures3−6 but also for their applications in nonlinear optical (NLO) materials,7,8 in optoelectronic devices,9,10 and as chiral ligands for asymmetric organic synthesis.11,12 Because of the helically twisted molecular orbitals involved in their electronic transitions, excellent chiroptical properties have been achieved using the π-conjugated helical geometry in terms of the large dissymmetry factors on the order of 10−3−10−2 both for absorption (gCD; CD, circular dichroism) and emission (gCPL; CPL, circular polarized luminescence), where gCD and gCPL are defined as gCD = 2(εL − εR)/(εL + εR) and gCPL = 2(IL − IR)/(IL + IR), in which ε is the molar absorption coefficient, I is the emission intensity, and subscripts L and R represent the properties corresponding to the left and right circularly polarized light, respectively.13,14 Extension of the π-electron system by condensing aromatic rings is a current emerging yet challenging issue in the field of organic chemistry, as exemplified by the recent impressive developments of graphene nanoribbons by Müllen and coworkers15−17 and carbon nanobelts by Itami and co-workers.18,19 By expanding π-conjugation, the properties desired for © XXXX American Chemical Society
application to functional materials can be expected, such as the band gap control for semiconducting materials with low redox potentials,20−22 photophysical response in the visible and nearinfrared wavelength regions,23,24 and adequate π−π stacking in the solid state causing a high carrier transportation.25,26 Graphene is an atomically thin 2-D conducting material that exhibits outstanding charge- and heat-transport properties.27−29 In contrast to the achiral nature of the 2-D single-layer graphenes, the helically twisted graphenes have a helical chirality (Figure 1a). Because of their helical molecular geometry, helical graphenes can be considered as one of the most promising candidates for the nanometer-sized molecular inductors that induce a magnetic field in nanometer dimensions when electric current flows through the helically twisted molecular framework30 and for the molecular spring materials that respond to microscopic forces.31 However, the precise synthesis of helically twisted polycyclic aromatic hydrocarbons with laterally π-extended structure remains largely underdeveloped, probably due to the lack of an available synthetic method; i.e., L-region-selective reactions are undeveloped in contrast to the K- and bay-region-selective reactions, where L-, Received: December 19, 2017
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DOI: 10.1021/jacs.7b13412 J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
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Figure 1. Chemical structure of helically twisted nanographenes. (a) Schematic illustration of a helical graphene, where the structure of hexa-perihexabenzo[7]helicene is highlighted in dark red on the left and the side view of the helical graphene with helicoid topology is shown on the right. (b) Chemical structures of hexa-peri-hexabenzo[7]helicene (1), 13,13′-bibenzo[b]perylenyl (2), and benzo[b]perylene as a reference compound (3) (R = t-Bu).
twisted C48H24 nanographene 1 has a small HOMO−LUMO band gap, as evidenced by the absorption edge that appeared at ca. 800 nm. The enantiomers of 1 isolated using a chiral HPLC, i.e., (P)- and (M)-1, showed CD signal with a high gCD value of larger than 10−2 in the near-infrared region (Δε = 74 M−1 cm−1, |gCD| = 0.016 at 680 nm). Interestingly, 1 showed an ultrafast dynamics of the S1 → S0 transition; the lifetime of the lowest-energy excited (S1) state of 1 was only a few picoseconds (τS1 = 1−2 ps), which is 4 orders of magnitude shorter than that of conventional unsubstituted carbo[7]helicene (τS1 = 14 ns).42
K-, and bay-regions correspond to the positions of the zigzag, convex armchair, and concave armchair sites in graphene structures, respectively.32,33 Recently, Collins and co-workers34 and Stará and co-workers35 independently reported pyrenebased π-extended helicene derivatives (∼C50H26), and Nuckolls and colleagues36 reported perylenediimide-based π-extended helicenes (∼C54H26). The π-extended helicenes, that is, polycyclic aromatic hydrocarbons consisting of two or more helicene-like subunits, have been investigated by the Itami (C58H28),37 Müllen (C66H46),38 and Kamikawa39 and Gingras40 (C66H36) research groups, though they are not a partial structure of the helical graphenes with single helicoid geometry. The π-extended helicenes reported so far, including the double helicenes, commonly show (1) relatively large HOMO− LUMO gap evidenced by the absorption edge in the short wavelength region (1.46 Å) were longer than those of the oddnumbered rings ( 28°) was observed for the inner helical rim of the even-numbered rings, which exhibited a significant single-bond character. Consequently, a tightly coiled helical molecular structure of 1 was clearly characterized by (1) the short vertical distance between the terminal rings (⟨dAG,GA⟩), (2) the small angle between the planes of the terminal rings (θAG), and (3) the large torsion angle along the inner helical rim (⟨ϕAG⟩). To investigate the local aromaticity of the homogeneously πextended [7]helicene 1, calculations of the nucleus-independent chemical shifts (NICS)59,60 and the anisotropy of currentinduced density (ACID)61,62 were conducted (Figure 4). According to the NICS calculations, positive NICS(0) values were found at the center of the even-numbered rings of 1 (D ring, +7.04 ppm; B and F rings, +6.40 ppm), while negative values were found at the other rings (A and G rings, −6.29 ppm; H−M rings, −5.65, −5.45, or −5.06 ppm; C and E rings, −1.28 ppm), suggesting the significant antiaromatic character of the B, D, and F rings (Figure 4a and Figure S3 of the Supporting Information). In the ACID plot of 1, counterclockwise paramagnetic ring currents appeared around the B, D, and F rings (Figure 4b and Figure S4 of the Supporting Information), supporting the antiaromatic character of the even-numbered rings. The results of the NICS values and the ACID plot were consistent with the single-bond character of the even-membered rings of 1, which represents the characteristic electronic state of the homogeneously π-extended helicene derivative. UV−Vis Absorption and DFT Calculations. Figure 5 shows the UV−vis absorption spectrum of 1 in toluene. In contrast to the π-extended 1,1′-binaphtyl 2, which shows absorption less than 470 nm (Figure S5, Supporting Information),43 1 showed a characteristic absorption band at 550−800 nm (λmax,abs = 675 nm, ε = 4700 M−1 cm−1) and a strong structured band at 400−500 nm (λmax,abs = 459 nm, ε = 40 000 M−1 cm−1). Absorption spectra of 1 measured at different concentrations were almost completely overlapped (Figure S6, Supporting Information), suggesting that no aggregation occurred, at least under dilute conditions, i.e., the concentrations from 10−6 to 10−5 M. According to the timedependent density functional theory (TD-DFT) calculations at
Figure 4. (a) NICS(0) values of 1 calculated at the GIAO-B3LYP/6311g(2d,p) level of theory. NICS(1) values are shown in parentheses. (b) ACID plot for 1 calculated at the CSGT-B3LYP/6-311g(2d,p) level of theory. The diamagnetic (clockwise) and paramagnetic (counterclockwise) ring currents under the magnetic field parallel to the z-axis are highlighted by red and blue arrows, respectively. An enlarged ACID plot is shown in Figure S4 of the Supporting Information.
Figure 5. Circular dichroism (top) and UV−vis absorption (bottom) spectra of 1 in toluene [red, (P)-(+)-1; blue, (M)-(−)-1]. The inset is a photograph of a solution of the helically twisted C 48 H 24 nanographene 1 in toluene.
the RTD-B3LYP/6-311g(2d,p) level of theory, the absorption band appeared at longer wavelength was attributed predominantly to the HOMO → LUMO transition (100%, f = 0.113, λmax,calc = 752 nm), and the structured band at shorter wavelength was assigned to a combination of the HOMO−1 → LUMO (59%) and the HOMO → LUMO+1 (39%) E
DOI: 10.1021/jacs.7b13412 J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
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Figure 6. Orbital correlation diagram of 1−3 calculated at the RTD-B3LYP/6-311g(2d,p) level of theory.
transitions (f = 0.392, λmax,calc = 468 nm) (Figure 5 and Figure S7 of the Supporting Information). Noteworthy, the formation of one single C−C bondfrom compounds 2 to 1caused a great impact on their excitation energies; the maximum wavelength of the lowest-energy absorption band was 675 nm for 1 in toluene and 446 nm for 2 in methylcyclohexane 43 (Figure S5, Supporting Information), suggesting strong orbital interactions between the two benzo[b]perylene subunits in 1. The low excitation energy of 1 was well-supported by TD-DFT calculations (Figure 6). The TD-DFT calculation suggested that the exciton energy of 2 (λmax,calc = 442 nm) was identical to that of benzo[b]perylene derivative 3 (λmax,calc = 442 nm), which is likely due to the small orbital interactions between the two benzo[b]perylene subunits of 2. Indeed, the HOMO−1 and HOMO of 2 degenerated each other, and their orbital energy (EH−1 = EH = −5.05 eV) was almost identical to the HOMO of 3 (EH = −5.06 eV). The same was true for the LUMOs of 2 (EL = −2.05 and EL+1 −1.92 eV) and LUMO of 3 (EL = −2.01 eV), albeit a small orbital interaction was seen in the LUMOs of 2 (ΔEL,L+1 = 0.13 eV). In contrast, large orbital interactions were seen in the HOMOs (ΔEH−1,H = 0.86 eV) and LUMOs (ΔEL,L+1 = 0.77 eV) of 1, which are responsible for the small HOMO−LUMO gap (ΔEH,L = 0.86 eV), resulting in the low excitation energy of 1 (λmax,calc = 752 nm). Thus, the characteristic lowest-energy absorption band extended up to 800 nm is attributed to the small HOMO−LUMO gap caused by the large energy separation between HOMO and HOMO− 1, as well as between LUMO and LUMO+1, which is a marked contrast to recently reported helically coiled graphene nanoribbons63 and π-extended helicenes.34−40 Chiroptical Properties. Enantiomers of 1 with helical chirality were separated by chiral high-performance liquid chromatography (HPLC) (Figure S8, Supporting Information), and their CD spectra were recorded in toluene (Figure 5, top). The first fraction eluted by chiral HPLC showed a positive Cotton effect at 500−800 nm (Δε = 74 M−1 cm−1, |gCD| = 0.016 at 680 nm) and a negative Cotton effect at 400−500 nm (Δε = −204 M−1 cm−1, |gCD| = 0.005 at 459 nm). The second fraction showed the identical shape and magnitude of CD
spectra with the opposite sign as the mirror image. It is noted that the CD signal observed in the near-infrared region (∼800 nm) is quite unique,64 and the large gCD value of more than 10−2 is relatively high compared to that of recently reported small organic molecules.13,39,65−68 On the basis of the comparison of experimental CD spectra with the result of TD-DFT calculations, the chirality of 1 was determined as (P)(+)-1 and (M)-(−)-1 (Figure S9, Supporting Information). The relationship between the helical chirality and the sign of the CD signal that appeared at the longest wavelength is consistent with that of the conventional carbo[n]helicenes.14 It is noted that the CD spectrum of 1 at 400−800 nm is very similar in shape to the absorption spectrum (Figure 5), which is in marked contrast to the exciton-coupled-type CD spectrum of 2 (Figure S5, Supporting Information). The resemblance between the shapes of the CD and absorption spectra suggests that a single exciton is delocalized over the whole molecular structure of 1, whereas two excitons are localized in each benzo[b]perylene subunit of 2 in the excited state. The rate of the helical inversion process of helicenes is a major concern in terms of applications for molecule-based materials with a single chirality.35−41,69−75 Martin et al. have reported that the racemization barriers of carbo[n]helicenes significantly depend on the size of the molecule, i.e., ΔG⧧ = 24.1, 36.2, and 41.7 kcal·mol−1 for [5]-, [6]-, and [7]helicenes, respectively.69,70 Vollhardt and co-workers have reported that an expanded helical phenylene, so-called [7]heliphene, shows a significantly low racemization barrier of ΔG⧧ = 12.6 kcal·mol−1 at −62 °C, likely because of the flexible molecular framework.71 Tilley and colleagues have recently reported another expanded helicene that showed a surprisingly low racemization barrier of ΔG⧧ = 10.7 kcal·mol−1 at −62 °C.72 In contrast to the flexible expanded helicenes, no racemization was experimentally detected for the π-extended double helicenes reported by the groups of Itami (C58H28)37 and Müllen (C66H46)38 even at 200 °C in diphenyl ether solution, which was supported by DFT calculations; the calculated ΔG⧧ values for the double helicenes were 43.5 kcal·mol−1 [calcd at the B3LYP/6-31g(d) level for C58H28]37 and 46.0 kcal·mol−1 [calcd at the B3LYP/6311g(d,p) level for C66H46],38 respectively. F
DOI: 10.1021/jacs.7b13412 J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
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Journal of the American Chemical Society Judging from the homogeneously π-extended [7]helicene structure, 1 is expected to show a large helical inversion barrier that is comparable or even higher than that of carbo[7]helicene (41.7 kcal·mol−1).69,70 Indeed, no racemization was detected in toluene at 90 °C for at least 20 h (Figure S10, Supporting Information). DFT calculations suggested that the activation barrier for the helical inversion process between (P)-(+)-1 and (M)-(−)-1 was calculated to be ΔG⧧ = 187.3 kJ·mol−1 (44.8 kcal·mol−1) at 298.15 K at the B3LYP/6-311g(2d,p) level of theory (Figure 7), which is higher than that of carbo[7]-
Figure 8. Time-resolved transient absorption spectra of 1 in toluene at room temperature, excited with a femtosecond 680 nm laser pulse. The inset shows the decay profiles monitored at 480 (top) and 800 nm (bottom).
state (S1 → S0). By integrating the spectral evolution with the analyses of time profiles of the transient absorbance (Figure S11, Supporting Information), we conclude that the S1 state deactivates into the ground state with a time constant of 1.2 ps and the vibrational cooling in the ground state follows with a time constant of 9.7 ps. From the results of TA measurements, the nonradiative decay rate for the S1 → S0 transition (knr) and the rate of vibrational cooling in the S0 state (kvc) were determined as knr = 8.3 × 1011 s−1 and kvc = 1.0 × 1011 s−1, respectively. Noteworthy, the lifetime of the S1 state of 1 (τS1 = 1.2 ps) is 4 orders of magnitude shorter than that of unsubstituted carbo[7]helicene (τS1 = 14 ns).42 Thus, we found that the helically twisted C48H24 nanographene molecule (1) is not fluorescent because of the ultrafast decay dynamics of the S1 state, which is more than 4 orders of magnitude faster than the theoretically estimated fluorescence emission rate; for example, the emission rate is estimated76 as kf,calc = 9 × 106 s−1 for a partially allowed electronic transition (f = 0.1) in the nearinfrared region (λem = 850 nm). The ultrafast decay dynamics is advantageous in terms of a fast and efficient response to light even under high photon density conditions, as well as a high resistance to photodegradation resulting from repeated photoexcitation cycles.
Figure 7. Racemization process between (P)-(+)-1 and (M)-(−)-1. The relative Gibbs free energy (kcal·mol−1) was calculated at the B3LYP/6-311g(2d,p) level of theory.
helicene. When the dispersion force was considered by an empirical correction in the DFT calculations, the activation barrier was found to increase to ΔG⧧ = 209.7 kJ·mol−1 (50.1 kcal·mol−1) at the B3LYP-GD3BJ/6-311g(2d,p) level of theory, suggesting that the stabilization by the intramolecular π−π interactions is likely prominent in the helical C2-geometry in the ground state compared to the saddle-shaped CS-geometry in the transition state. Excited-State Dynamics. Despite the rigid molecular framework of 1 having a moderate oscillator strength for the HOMO−LUMO transition ( f = 0.113), no emission was observed in the wavelength range of 800−1500 nm either at room temperature in toluene or even at low temperature (T = 80 K) in 2-methyltetrahydrofuran, which forms a glass state below 137 K. To investigate the singlet excited state dynamics of the helically twisted C48H24 nanographene molecule 1, transient absorption (TA) measurements were carried out at room temperature. Figure 8 shows time-resolved TA spectra of 1 in toluene, excited with a femtosecond laser pulse at 680 nm. The TA spectra showed the appearance of the positive bands in the wavelength region shorter than 410 nm and longer than 470 nm, together with the negative band around 450 nm. These positive bands could be ascribed to the Sn ← S1 absorption because these bands appeared within the response of the apparatus. On the other hand, the negative one was safely ascribable to the bleaching signal of the ground-state absorption. With an increase in the delay time after the excitation, the positive bands decreased and the negative one recovered. Within a few picoseconds following the excitation, the positive absorption bands >510 nm almost completely disappeared and the positive absorption around 480 nm gradually decreased in a few tens of picoseconds time region, which could be attributed to the vibrational cooling in the ground state following the nonradiative decay from the excited
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CONCLUSION In summary, we have synthesized hexa-peri-hexabenzo[7]helicene (1) as a primary substructure of helical graphenes. Single-crystal X-ray analysis unambiguously determined the πextended helicoid geometry of the helically twisted C48H24 nanographene. Homogeneous π-extension throughout the helical geometry was a key molecular design to realize (1) the small HOMO−LUMO gap and (2) a single exciton delocalization over the whole molecular structure in the excited state. The precise synthesis of helically twisted nanographenes opens up a field of helical nanocarbon chemistry that can develop the nanometer-sized molecular inductors, spin filters, and molecular spring materials responding to microscopic forces.
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EXPERIMENTAL SECTION
Synthesis of Hexa-peri-hexa(1,3-propylene)[7]helicene (13). To a solution of zinc powder (5.8 × 102 mg, 8.9 mmol) in dry THF (8 mL) was added TiCl4 (1.2 × 102 mg, 5.9 mmol). A solution of G
DOI: 10.1021/jacs.7b13412 J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
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Journal of the American Chemical Society octahydrodibenzo[b,n]perylene-1,14-dione (6, 1.2 × 102 mg, 0.31 mmol) and α-tetralone (6.6 × 102 mg, 4.5 mmol) in dry THF (40 mL) was then added to the reaction mixture. The solution was refluxed for 8 h and cooled to room temperature, and then aq HCl (1 N, ca. 100 mL) was added. The reaction product was extracted with hexane and ethyl acetate, washed with water, dried over MgSO4, filtrated, and evaporated. The crude product was purified by silica gel column chromatography (hexane/CH2Cl2 = 95/5 to 85/15) and GPC, to remove the dimer of α-tetralone, to give compound 7 (87 mg, 0.14 mmol, 45%) as a yellow solid, which was used for next reaction without further purification. We note that the production of 7 was confirmed by EI-MS. The 1H NMR spectrum of the product was very complicated, probably due to it being a mixture of trans/cis isomers. Compound 7 (1.5 × 102 mg, 0.24 mmol), iodine (1.5 × 102 mg, 0.59 mmol), and propylene oxide (20 mL) were dissolved in 1,4-dioxane (300 mL). The solution was passed through a photochemical flow reactor system (450 W high-pressure Hg lamp, 30−40 loops of FEP tubing) at a specified flow rate (30.6 mL/min). The resulting solution was concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (hexane/CH2Cl2 = 85/ 15) and GPC to give 13 (27 mg, 0.044 mmol, 19%) as a yellow solid. 1 H NMR (500 MHz, CDCl3, δ): 1.69−1.79 (m, 2H), 1.95−2.04 (m, 2H), 2.04−2.12 (m, 2H), 2.13−2.28 (m, 6H), 2.69−2.82 (m, 6H), 2.85−2.95 (m, 4H), 3.05−3.14 (m, 6H), 3.15−3.31 (m, 8H), 6.10 (dd, J = 6.8 Hz, 8.5 Hz, 2H), 6.56 (d, J = 7.0 Hz, 2H), 6.62 (d, J = 8.5 Hz, 2H). 13C NMR (125 MHz, CDCl3, δ): 22.8 (2C), 23.3 (4C), 27.0 (2C), 27.65 (2C), 27.70 (2C), 27.8 (2C), 28.0 (2C), 31.1 (2C), 121.6 (2C), 122.3 (2C), 123.4 (2C), 124.2 (2C), 125.9 (2C), 126.92 (2C), 126.97 (2C), 127.0 (2C), 127.3 (2C), 128.6 (2C), 128.7 (2C), 128.8 (2C), 129.3 (2C), 129.4 (2C), 133.3 (2C). HRMS−APCI−Orbitrap (m/z): [M + H]+ calcd for C48H43+ 619.3359, found 619.3349. Synthesis of Hexa-peri-hexabenzo[7]helicene (1). A solution of compound 13 (15 mg, 24 μmol) in toluene (13 mL) was degassed by freeze−pump−thaw cycles five times and then heated up to 90 °C. After the addition of 2,3-dichloro-5,6-dicyanoquinone (DDQ, 44 mg, 1.9 × 102 μmol) at that temperature, the resulting solution was stirred at 90 °C for 5 min under a nitrogen atmosphere. Then the solution was cooled and immediately quenched by the addition of aq Na2S2O3 (concd, ca. 10 mL). The reaction product was extracted with toluene, and the combined organic layers were evaporated to dryness. The crude product was purified by silica gel column chromatography (hexane/CH2Cl2 = 85/15) and GPC to give 1 (3.5 mg, 5.8 μmol, 24%) as a deep green solid. Mp: >450 °C. It is noted that longer reaction time at 90 °C in the presence of DDQ resulted in a decrease of the reaction yield. 1H NMR (600 MHz, CDCl3, δ): 6.22 (t, J = 7.8 Hz, 2H), 6.69 (d, J = 8.4 Hz, 2H), 7.12 (d, J = 8.4 Hz, 2H), 7.27 (t, J = 7.8 Hz, 2H), 7.63 (t, J = 7.8 Hz, 2H), 7.80 (d, J = 7.5 Hz, 2H), 7.93 (d, J = 7.2 Hz, 2H), 8.15 (d, J = 7.2 Hz, 2H), 8.34 (d, J = 7.2 Hz, 2H), 8.47 (d, J = 7.8 Hz, 2H), 8.49 (d, J = 8.4 Hz, 2H). 13C NMR (151 MHz, CDCl3, δ): 119.9, 121.5, 122.0, 122.4, 122.7, 125.51, 125.54, 125.8, 126.7, 126.89, 126.92, 127.2, 128.0, 128.5, 129.7, 130.1, 130.2, 130.3, 131.03, 131.09, 133.5, 134.0. HRMS−APCI−Orbitrap (m/z): [M + H]+ calcd for C48H25+ 601.1951, found 601.1939. X-ray Crystallography. X-ray crystallographic analysis was performed on a Rigaku R-AXIS RAPID-S diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.710 75 Å). The structures were solved by direct methods (SIR-2014) and refined by full-matrix least-squares techniques against F2 (SHELXL-2014). All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were placed using AFIX instructions. Transient Absorption Spectroscopy. Transient absorption (TA) spectra were measured by using a home-built setup with a Ti:sapphire regenerative amplifier (Spitfire, Spectra-Physics, 802 nm, 100 fs, 1 mJ/pulse, 1 kHz). The delay times between the excitation and probe pulses were controlled with an optical delay stage. The instrumental response time was typically 120 fs. The sample solution was filled into a 2 mm homemade rotation cell with a pair of 1 mm quartz windows. Steady-state absorption spectra were recorded before and after the measurement, and the absorbance change of the sample
was less than 1%, showing that the photodegradation of the sample is negligibly small. Theoretical Calculations. The geometrical optimization was carried out at the B3LYP/6-311g(2d,p) level of theory implemented in the Gaussian 09 package. Convergence at a local minimum structure was confirmed by no imaginary frequencies on frequency analysis. Successively, the optimized local minimum structures were subjected to time-dependent density functional theory (TD-DFT) calculations to obtain excited states at the same level of theory. An ultrafine grid was used for all DFT calculations (specified by the keyword “Int = Ultrafine”). Nucleus-independent chemical shifts (NICS) values were calculated at the GIAO-B3LYP/6-311g(2d,p) level of theory. The anisotropy of the current-induced density (ACID) plot was calculated at the CSGT-B3LYP/6-311g(2d,p) level of theory using the Gaussian 09 package [specified by the keywords “NMR = CSGT” and “IOp(10/ 93 = 1)”] and the AICD 2.0.0 program. The theoretically estimated fluorescence emission rate (kf,calc) was calculated as follows76
k f,calc =
2πe 2 2 νex̃ f = (6.67 × 10−5)νex̃ 2f ε0mec
where e is the elementary charge, me is the mass of an electron, ε0 is the vacuum permittivity, c is the speed of light in a vacuum, ν̃ex is the de-excitation energy (m−1), and f is the oscillator strength of the deexcitation transition.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/jacs.7b13412. Experimental procedures, details of the X-ray singlecrystal analyses, and theoretical calculations, as well as 1H and 13C NMR spectra (PDF) X-ray single-crystal data of 1 in CIF format (CIF)
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AUTHOR INFORMATION
Corresponding Authors
*
[email protected] *
[email protected] ORCID
Takashi Hirose: 0000-0002-5351-2101 Hiroshi Miyasaka: 0000-0002-6020-6591 Kenji Matsuda: 0000-0002-2420-4214 Notes
The authors declare no competing financial interest. CCDC 1585563 contains the details of crystallographic data of 1, which is available from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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ACKNOWLEDGMENTS This work was supported by the JSPS KAKENHI Grant Number JP26107008 for Scientific Research on Innovative Areas “Photosynergetics”. We thank Dr. Tomohiro Higashino and Prof. Hiroshi Imahori (Department of Molecular Engineering, Graduate School of Engineering, Kyoto University) for assistance with fluorescence spectroscopic measurements in the near-infrared region at low temperatures. We also thank Prof. Rainer Herges (Institut für Organische Chemie, Universität Kiel) for providing the AICD 2.0.0 program.
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REFERENCES
(1) Shen, Y.; Chen, C.-F. Chem. Rev. 2012, 112, 1463−1535. (2) Gingras, M. Chem. Soc. Rev. 2013, 42, 1051−1095.
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DOI: 10.1021/jacs.7b13412 J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
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Journal of the American Chemical Society (3) Gingras, M.; Félix, G.; Peresutti, R. Chem. Soc. Rev. 2013, 42, 1007−1050. (4) Šámal, M.; Chercheja, S.; Rybácě k, J.; Vacek Chocholoušová, J.; Vacek, J.; Bednárová, L.; Šaman, D.; Stará, I. G.; Starý, I. J. Am. Chem. Soc. 2015, 137, 8469−8474. (5) Geng, X.; Donahue, J. P.; Mague, J. T.; Pascal, R. A., Jr. Angew. Chem., Int. Ed. 2015, 54, 13957−13960. (6) Kawasumi, K.; Zhang, Q.; Segawa, Y.; Scott, L. T.; Itami, K. Nat. Chem. 2013, 5, 739−744. (7) Verbiest, T.; Van Elshocht, S.; Kauranen, M.; Hellemans, L.; Snauwaert, J.; Nuckolls, C.; Katz, T. J.; Persoons, A. Science 1998, 282, 913−915. (8) Fox, J. M.; Katz, T. J.; Van Elshocht, S.; Verbiest, T.; Kauranen, M.; Persoons, A.; Thongpanchang, T.; Krauss, T.; Brus, L. J. Am. Chem. Soc. 1999, 121, 3453−3459. (9) Yang, Y.; Correa da Costa, R.; Fuchter, M. J.; Campbell, A. J. Nat. Photonics 2013, 7, 634−638. (10) Kiran, V.; Mathew, S. P.; Cohen, S. R.; Hernandez Delgado, I.; Lacour, J.; Naaman, R. Adv. Mater. 2016, 28, 1957−1962. (11) Narcis, M. J.; Takenaka, N. Eur. J. Org. Chem. 2014, 2014, 21− 34. (12) Yavari, K.; Aillard, P.; Zhang, Y.; Nuter, F.; Retailleau, P.; Voituriez, A.; Marinetti, A. Angew. Chem., Int. Ed. 2014, 53, 861−865. (13) Sánchez-Carnerero, E. M.; Agarrabeitia, A. R.; Moreno, F.; Maroto, B. L.; Muller, G.; Ortiz, M. J.; de la Moya, S. Chem. - Eur. J. 2015, 21, 13488−13500. (14) Furche, F.; Ahlrichs, R.; Wachsmann, C.; Weber, E.; Sobanski, A.; Vögtle, F.; Grimme, S. J. Am. Chem. Soc. 2000, 122, 1717−1724. (15) Ruffieux, P.; Wang, S.; Yang, B.; Sánchez-Sánchez, C.; Liu, J.; Dienel, T.; Talirz, L.; Shinde, P.; Pignedoli, C. A.; Passerone, D.; Dumslaff, T.; Feng, X.; Müllen, K.; Fasel, R. Nature 2016, 531, 489− 473. (16) Chen, L.; Hernandez, Y.; Feng, X.; Müllen, K. Angew. Chem., Int. Ed. 2012, 51, 7640−7654. (17) Cai, J.; Ruffieux, P.; Jaafar, R.; Bieri, M.; Braun, T.; Blankenburg, S.; Muoth, M.; Seitsonen, A. P.; Saleh, M.; Feng, X.; Müllen, K.; Fasel, R. Nature 2010, 466, 470−473. (18) Povie, G.; Segawa, Y.; Nishihara, T.; Miyauchi, Y.; Itami, K. Science 2017, 356, 172−175. (19) Wegner, H. A. Angew. Chem., Int. Ed. 2017, 56, 10995−10996. (20) Zeng, W.; Phan, H.; Herng, T. S.; Gopalakrishna, T. Y.; Aratani, N.; Zeng, Z.; Yamada, H.; Ding, J.; Wu, J. Chem. 2017, 2, 81−92. (21) Pschirer, N. G.; Kohl, C.; Nolde, F.; Qu, J.; Müllen, K. Angew. Chem., Int. Ed. 2006, 45, 1401−1404. (22) Tsuda, A.; Osuka, A. Science 2001, 293, 79−82. (23) Barbieri, A.; Bandini, E.; Monti, F.; Praveen, V. K.; Armaroli, N. Top Curr. Chem. 2016, 374, 47. (24) Escobedo, J. O.; Rusin, O.; Lim, S.; Strongin, R. M. Curr. Opin. Chem. Biol. 2010, 14, 64−70. (25) Takimiya, K.; Osaka, I.; Mori, T.; Nakano, M. Acc. Chem. Res. 2014, 47, 1493−1502. (26) Coropceanu, V.; Cornil, J.; da Silva Filho, D. A.; Olivier, Y.; Silbey, R.; Brédas, J.-L. Chem. Rev. 2007, 107, 926−952. (27) Castro Neto, A. H.; Guinea, F.; Peres, N. M. R.; Novoselov, K. S.; Geim, A. K. Rev. Mod. Phys. 2009, 81, 109−162. (28) Novoselov, K. S.; Fal'ko, V. I.; Colombo, L.; Gellert, P. R.; Schwab, M. G.; Kim, K. Nature 2012, 490, 192−200. (29) Han, H.; Zhang, Y.; Wang, N.; Samani, M. K.; Ni, Y.; Mijbil, Z. Y.; Edwards, M.; xiong, S.; Säas̈ kilahti, K.; Murugesan, M.; Fu, Y.; Ye, L.; Sadeghi, H.; Bailey, S.; Kosevich, Y. A.; Lambert, C. J.; Liu, J.; Volz, S. Nat. Commun. 2016, 7, 11281. (30) Xu, F.; Yu, H.; Sadrzadeh, A.; Yakobson, B. I. Nano Lett. 2016, 16, 34−39. (31) Guo, Y.-D.; Yan, X.-H.; Xiao, Y.; Liu, C.-S. Sci. Rep. 2015, 5, 16731. (32) Ito, H.; Ozaki, K.; Itami, K. Angew. Chem., Int. Ed. 2017, 56, 11144−11164. (33) Ozaki, K.; Kawasumi, K.; Shibata, M.; Ito, H.; Itami, K. Nat. Commun. 2015, 6, 6251.
(34) Bédard, A.-C.; Vlassova, A.; Hernandez-Perez, A. C.; Bessette, A.; Hanan, G. S.; Heuft, M. A.; Collins, S. K. Chem. - Eur. J. 2013, 19, 16295−16302. (35) Buchta, M.; Rybácě k, J.; Jančařík, A.; Kudale, A. A.; Buděsí̌ nský, M.; Chocholoušová, J. V.; Vacek, J.; Bednárová, L.; Císařová, I.; Bodwell, G. J.; Starý, I.; Stará, I. G. Chem. - Eur. J. 2015, 21, 8910− 8917. (36) Schuster, N. J.; Paley, D. W.; Jockusch, S.; Ng, F.; Steigerwald, M. L.; Nuckolls, C. Angew. Chem., Int. Ed. 2016, 55, 13519−13523. (37) Fujikawa, T.; Segawa, Y.; Itami, K. J. Am. Chem. Soc. 2015, 137, 7763−7768. (38) Hu, Y.; Wang, X.-Y.; Peng, P.-X.; Wang, X.-C.; Cao, X.-Y.; Feng, X.; Müllen, K.; Narita, A. Angew. Chem., Int. Ed. 2017, 56, 3374−3378. (39) Hosokawa, T.; Takahashi, Y.; Matsushima, T.; Watanabe, S.; Kikkawa, S.; Azumaya, I.; Tsurusaki, A.; Kamikawa, K. J. Am. Chem. Soc. 2017, 139, 18512−18521. (40) Berezhnaia, V.; Roy, M.; Vanthuyne, N.; Villa, M.; Naubron, J.V.; Rodriguez, J.; Coquerel, Y.; Gingras, M. J. Am. Chem. Soc. 2017, 139, 18508−18511. (41) Harada, N.; Nakanishi, K. Circular Dichroic Spectroscopy: Exciton Coupling in Organic Stereochemistry; University Science Books and Oxford University Press, 1983. (42) Birks, J. B.; Birch, D. J. S.; Cordemans, E.; Vander Donckt, E. Chem. Phys. Lett. 1976, 43, 33−36. (43) Uchida, Y.; Hirose, T.; Nakashima, T.; Kawai, T.; Matsuda, K. Org. Lett. 2016, 18, 2118−2121. (44) Müller, M.; Iyer, V. S.; Kübel, C.; Enkelmann, V.; Müllen, K. Angew. Chem., Int. Ed. Engl. 1997, 36, 1607−1610. (45) Scholz, M.; Mühlstädt, M.; Dietz, F. Tetrahedron Lett. 1967, 8, 665−668. (46) Flammang-Barbieux, M.; Nasielski, J.; Martin, R. H. Tetrahedron Lett. 1967, 8, 743−744. (47) Mori, K.; Murase, T.; Fujita, M. Angew. Chem., Int. Ed. 2015, 54, 6847−6851. (48) Laarhoven, W. H.; Cuppen, Th. J. H. M.; Nivard, R. J. J. Tetrahedron 1970, 26, 4865−4881. (49) Flynn, A. B.; Ogilvie, W. W. Chem. Rev. 2007, 107, 4698−4745. (50) Ephritikhine, M. Chem. Commun. 1998, 2549−2554. (51) Tanaka, K.; Suzuki, H.; Osuga, H. J. Org. Chem. 1997, 62, 4465− 4470. (52) Dubois, F.; Gingras, M. Tetrahedron Lett. 1998, 39, 5039−5040. (53) Liu, L.; Yang, B.; Katz, T. J.; Poindexter, M. K. J. Org. Chem. 1991, 56, 3769−3775. (54) Joly, M.; Defay, N.; Martin, R. H.; Declerq, J. P.; Germain, G.; Soubrier-Payen, B.; Van Meerssche, M. Helv. Chim. Acta 1977, 60, 537−560. (55) Dahl, T. Acta Chem. Scand. 1994, 48, 95−106. (56) Hunter, C. A.; Sanders, J. K. M. J. Am. Chem. Soc. 1990, 112, 5525−5534. (57) Stevens, B. Spectrochim. Acta 1962, 18, 439−448. (58) Collins, S. K.; Grandbois, A.; Vachon, M. P.; Côté, J. Angew. Chem., Int. Ed. 2006, 45, 2923−2926. (59) Schleyer, P. v. R.; Maerker, C.; Dransfeld, A.; Jiao, H.; van Eikema Hommes, N. J. R. J. Am. Chem. Soc. 1996, 118, 6317−6318. (60) Chen, Z.; Wannere, C. S.; Corminboeuf, C.; Puchta, R.; Schleyer, P. v. R. Chem. Rev. 2005, 105, 3842−3888. (61) Herges, R.; Geuenich, D. J. Phys. Chem. A 2001, 105, 3214− 3220. (62) Geuenich, D.; Hess, K.; Köhler, F.; Herges, R. Chem. Rev. 2005, 105, 3758−3772. (63) Daigle, M.; Miao, D.; Lucotti, A.; Tommasini, M.; Morin, J.-F. Angew. Chem., Int. Ed. 2017, 56, 6213−6217. (64) Hasegawa, M.; Kobayakawa, K.; Matsuzawa, H.; Nishinaga, T.; Hirose, T.; Sako, K.; Mazaki, Y. Chem. - Eur. J. 2017, 23, 3267−3271. (65) Nishimura, H.; Tanaka, K.; Morisaki, Y.; Chujo, Y.; Wakamiya, A.; Murata, Y. J. Org. Chem. 2017, 82, 5242−5249. (66) Sato, S.; Yoshii, A.; Takahashi, S.; Furumi, S.; Takeuchi, M.; Isobe, H. Proc. Natl. Acad. Sci. U. S. A. 2017, 114, 13097−13101. I
DOI: 10.1021/jacs.7b13412 J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
Article
Journal of the American Chemical Society (67) Goto, T.; Okazaki, Y.; Ueki, M.; Kuwahara, Y.; Takafuji, M.; Oda, R.; Ihara, H. Angew. Chem., Int. Ed. 2017, 56, 2989−2993. (68) Saikawa, M.; Nakamura, T.; Uchida, J.; Yamamura, M.; Nabeshima, T. Chem. Commun. 2016, 52, 10727−10730. (69) Martin, R. H.; Marchant, M. J. Tetrahedron 1974, 30, 347−349. (70) Janke, R. H.; Haufe, G.; Würthwein, E.-U.; Borkent, J. H. J. Am. Chem. Soc. 1996, 118, 6031−6035. (71) Han, S.; Bond, A. D.; Disch, R. L.; Holmes, D.; Schulman, M.; Teat, S. J.; Vollhardt, K. P. C.; Whitener, G. D. Angew. Chem., Int. Ed. 2002, 41, 3223−3227. (72) Kiel, G. R.; Patel, S. C.; Smith, P. W.; Levine, D. S.; Tilley, T. D. J. Am. Chem. Soc. 2017, 139, 18456−18459. (73) Yang, W.; Longhi, G.; Abbate, S.; Lucotti, A.; Tommasini, M.; Villani, C.; Catalano, V. J.; Lykhin, A. O.; Varganov, S. A.; Chalifoux, W. A. J. Am. Chem. Soc. 2017, 139, 13102−13109. (74) Meng, D.; Fu, H.; Xiao, C.; Meng, X.; Winands, T.; Ma, W.; Wei, W.; Fan, B.; Huo, L.; Doltsinis, N. L.; Li, Y.; Sun, Y.; Wang, Z. J. Am. Chem. Soc. 2016, 138, 10184−10190. (75) Li, C.; Yang, Y.; Miao, Q. Chem. Asian J. DOI: 10.1002/ asia.201800073 (online early access). (76) Kubo, H.; Hirose, T.; Matsuda, K. Org. Lett. 2017, 19, 1776− 1779.
J
DOI: 10.1021/jacs.7b13412 J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
