Photophysical properties of quinoxaline-fused [7]carbohelicene derivatives

Abstract

Helicene and its derivatives have received considerable attention as candidates for organic photoelectronic materials. Recently, novel quinoxaline-fused [7]carbohelicene derivatives have exhibited unique structural and photophysical properties, especially in the crystal state. However, their structure–property relationships have not been fully understood from their micromechanisms, which is also important to further improve their performance. Herein, the electronic transitions, electronic circular dichroism (CD), second-order nonlinear optical (NLO) responses and charge transport properties of five quinoxaline-fused [7]carbohelicene derivatives have been investigated based on density functional theory calculations. The experimental UV-Vis/CD spectra of the studied compounds were reproduced well by our calculations. Thus, we can assign their electron transition properties and absolution configurations (ACs) with high confidence. It is found that the CD bands of quinoxaline-fused [7]carbohelicene derivatives mainly originate from exciton coupling between quinoxaline, phenyl or 4-methoxyphenyl groups and [7]carbohelicene, which is in sharp contrast to [7]carbohelicene. More interestingly, these derivatives possess large first hyperpolarizability values. For example, the β_HRS value of compound 6 is 32.96 × 10⁻³⁰ esu, which is about 190 times larger than that of the organic urea molecule. The bandwidth of the valence band of compound 2 is comparable to that of the conduction band and slightly larger than that of tris(8-hydroxyquinolinato)aluminium. This means that compound 2 is a potential candidate as an ambipolar charge transport material.

---

1. Introduction

Chirality is not only vital to our life but also plays an important role in material science.^1–5 Thus, much effort has been made towards controlling and understanding chirality in chemical synthesis and material design. Helicenes are polycyclic aromatic compounds with screw-shaped skeletons formed by ortho-fused benzene or other aromatic rings.^6–9 Steric hindrance interactions between the terminal aromatic rings endow helicenes with helical chirality. As a consequence, helicenes exhibit high optical rotation and circular dichroism values in the visible region.^10–17 More interestingly, due to their dissymmetric backbones, helicenes and their derivatives have applications in many fields (e.g. asymmetric catalysis,^18–21 liquid crystal molecules,²² enantioselective fluorescent sensors,²³ rotors,²⁴ nonlinear optics,^25–27 molecular recognition^28–31 and organic electronics^32–36).

Among the carbohelicene family, [7]carbohelicene is the most interesting member due to its high optical stability (its racemization barrier is 40.5 kcal mol⁻¹),^37,38 easy decoration and functionization, and distinguishable photophysical properties.^37,39,40 For example, [7]carbohelicene can function as a “molecular tweezer”^41–43 of some metallic cations. Fascinating chiroptical properties have been observed by introducing silver(I) ion moieties into [7]carbohelicene.³⁷ Facchetti et al. reported that tetrathia-[7]-helicene derivatives act as p-type semiconductors with high carrier mobilities in organic thin-film transistors.^44,45 2,12-dihexyl-2,12-diaza[7]helicene can serve as a deep-blue dopant emitter in an organic light-emitting diode.⁴⁶ Moreover, [7]carbohelicene can be easily functionalized by varying the substituents. Specifically, the photophysical properties of tetrathia-[7]-helicene can be greatly modulated by decorating the two terminal thiophene rings.^47,48 Specifically, novel organometallic Ru(II) and Fe(II) complexes with tetrathia-[7]-helicene have been synthesized. Studies show that tetrathia-[7]-helicene and their Ru(II) and Fe(II) complexes are good candidates for second-order NLO materials.^27,49

Quinoxalines (i.e. benzopyrazine) can be easily synthesized from diketones and diamines.⁵⁰ Quinoxaline has strong electron-withdrawing abilities which originate from the two unsaturated nitrogen atoms in the pyrazine ring. Due to the highly polarized nature of the imine units, quinoxalines are extensively used as light-emitting and electron-transporting materials.⁵¹ Moreover, the incorporation of a quinoxaline unit might enable the formation of CH⋯N interactions and influence the crystal packing.⁵² As a consequence, the quinoxaline units are expected to enhance the luminous efficiency and to control the packing structures in the crystal. Recently, Sakai et al. synthesized a series of quinoxaline-fused [7]carbohelicenes (Fig. 1). It is found that incorporating quinoxaline into [7]carbohelicene greatly enhances the fluorescence quantum yield. Specifically, the fluorescence quantum yield of compound 2 is about four times greater than that of compound 1. Notably, quinoxaline-fused [7]carbohelicene derivatives can possess unique crystal packing. For example, compound 2 possesses racemic crystal packing through intermolecular interactions (π⋯π, CH⋯N and CH⋯π). One-dimensional helical columns were firstly observed which contain the racemic compound 4. This helical columnar structure contains both π–π stacking and CH⋯N interactions, which is in sharp contrast to the packing motif of the corresponding enantiomer. Moreover, the excimer-like delocalized excited state was clearly observed by time-resolved fluorescence measurements.⁵¹

Fig. 1 Chemical structures of the studied compounds 1–6.

It is well known that macroscopic properties strongly correlate with microcosmic electron structures, especially for electron transition properties upon excitation. As far as we know, only the frontier molecular orbital levels of quinoxaline-fused [7]carbohelicene derivatives have been studied at the B3LYP/6-31G* level of theory.⁵¹ By all appearances, it is necessary to systemically investigate the photophysical properties of these compounds and establish their structure–property relationships at the quantum chemistry level of theory. The main aims of the current investigation were (i) to evaluate the reliability of TDDFT in simulating the UV-Vis/CD spectra of the studied compounds, (ii) to assign their absolute configurations (ACs), (iii) to describe their electronic transition properties and chiroptical origins, and (iv) to investigate their NLO and charge transport properties and determine their potential applications in the materials science field.

2. Computational details

Geometrical optimization of the studied compounds was carried out using the B3LYP⁵³ functional as implemented in the Gaussian 09 computational program suite.⁵⁴ During the process of optimization, there were no symmetry or internal coordination constraints. The B3LYP functional is a combination of Becke's three-parameter hybrid exchange functional^53,55 and the Lee–Yang–Parr⁵⁶ correlation functional. Basis sets of 6-31G(d,p) for C, O, N, and H atoms were applied. The harmonic vibration calculation was used to confirm their minima.

To investigate the linear and chiroptical properties of the studied compounds, their electron excitation energies, oscillator strengths, and rotational strengths were calculated at the TDB3LYP/6-31+G(d) level of theory. Both length and velocity representations were used to obtain the rotational strengths. It is noted that the velocity-gauge representation of the dipole operator is gauge origin independent. Gaussian bandshapes⁵⁷ with a bandwidth of 0.12 eV were used to compare the calculated UV-Vis/CD spectra with experimental spectra. The effects of different basis sets and DFT functionals on the UV-Vis/CD spectra were also tested. To test the effect of solvent on the CD spectra, the LR-PCM model^58,59 was utilized as implemented in Gaussian 09. The solvent tetrahydrofuran (THF) was treated as a continuous dielectric environment with a dielectric constant of 7.4257.

The first hyperpolarizability was calculated as performed in the Gaussian 09 program package. It is noted that hyper-Rayleigh scattering (HRS) was used to determine the second-order nonlinear optical response (NLO) properties. In the case of plane-polarized incident light and observations made perpendicular to the propagation plane without polarization analysis of the scattered beam, the second-order NLO response that can be extracted from HRS data can be described as:^60,61

〈β_ZZZ²〉 and 〈β_XZZ²〉 correspond to the orientational average of the β tensor without assuming Kleinman's conditions.⁶² Here, we only were concerned with the static first hyperpolarizability. Therefore, the frequency value in eqn (1) was set to zero.

To investigate the electronic properties in bulk, an electronic band structure calculation was performed by a DFT method as implemented in the Vienna Ab initio Simulation Package (VASP)^63,64 with Perdew–Burke–Ernzerhof (PBE) for the exchange correlation functionals and a plane-wave basis set with an energy cut-off of 400 eV. The Monkhorst–Pack scheme was used to sample the Brillouin zone with a grid spacing of 2π × 0.04 Å⁻¹.

3. Results and discussion

3.1. Molecular structures

In this paper, five quinoxaline-fused [7]carbohelicene derivatives were investigated (Fig. 1). To test the influence of quinoxaline on the electronic properties, [7]carbohelicene was also included. Compounds 2–4 have been synthesized and characterized by X-ray crystallography.⁵¹ Compounds 5 and 6 were designed to investigate their charge transfer cooperativity and find effective ways to enhance their NLO response. The geometric structures of the studied compounds were fully optimized without any symmetry constraints at the B3LYP/6-31G(d,p) level of theory. The absence of the imaginary frequencies confirms that our optimized structures are minima. It is noted that the optimized geometries of the studied compounds have C₁ symmetry. Here, compound 4 is taken as an example to test our adopted method; its main structural parameters were reproduced well by our calculations (Table S1†). Thus, the adopted basis set and functional are suitable to describe molecular structures for the studied compounds.

3.2. The selection of the basis sets and functionals for the studied compounds

The time-dependent density functional theory (TDDFT) method has extensively been employed to investigate the electronic transition properties^65–70 and chiroptical properties^71–80 of diverse compounds. In general, electronic transition properties are sensitive to basis sets^81–84 and DFT functionals,^85–93 especially for CD calculations. For our studied compounds, Sakai et al. only calculated their frontier molecular orbital levels at the B3LYP/6-31G* level.⁵¹ The electronic transition properties of these compounds have not been systematically studied thus far. As a consequence, five Pople's basis sets: 6-31G(d), 6-31+G(d), 6-31++G(d,p), 6-311++G(d,p), and 6-311++G(2d,2p) were selected to assess the influence of the basis set extension on the absorption wavelengths using the B3LYP functional, which is the most popular functional for organic compounds. For compound 2, an intense absorption band at 276 nm and three moderately intense absorption bands at 332, 366 and 427 nm were observed.⁵¹ The computed absorption wavelengths at the different basis set levels are listed in Table S2.† It is noted that the four observed bands are reproduced well by our calculations. Moreover, the difference between the absorption wavelengths of the largest basis set and the smallest basis set is within 8 nm, which means the effect of the basis set size on the calculated absorption wavelengths is negligible. Previous studies have shown that diffuse functions play a vital role in obtaining accurate absorption wavelengths and describing the electronic transition properties.⁹⁴ Thus, the 6-31+G(d) basis set was used in the following calculations. Subsequently, five DFT functionals: B3PW91,^95–97 M06-2X,^98,99 BH&HLYP,^100,101 PBE0,^102,103 and B3LYP,⁵³ were selected to evaluate the influence of these DFT functionals on the absorption wavelengths. The simulated UV-Vis and CD spectra using these functionals along with the experimental spectra are given in Fig. S1.† The results show that the computed absorption wavelengths strongly depend on the functionals used. Specifically, the M06-2X and BH&HLYP functionals could not reproduce the experimental absorption band at about 427 nm. The same trend was also observed in the simulated CD spectra. This observation might result from the larger energy gaps of the M06-2X and BH&HLYP functionals (Table S3†). However, both the band positions and shapes of the B3LYP, B3PW91 and PBE0 functionals are similar, which might be due to their similar HF exchange fractions. It is well known that conventional TDDFT methods usually underestimate charge-transfer excitations due to semi-local exchange-correlation effects. Studies have shown that range-separated functionals (e.g. LC-BLYP and LC-PBE) can give correct localizations, HOMO–LUMO gaps, and ionization/electron affinity energies. For example, the range-separated functionals have successfully described the optoelectronic and excitonic properties of oligoacenes.^104,105 Thus, we also selected the LC-BLYP functional to calculate the electronic excitation properties for compound 2. The experimental spectra of compound 2 were not reproduced well by the LC-BLYP functional (Fig. S1†). Overall, the results computed with the B3LYP functional are much closer to the experimental results. Thus, the B3LYP functional combined with the 6-31+G(d) basis set was employed in the following calculations.

3.3. UV-Vis and CD spectra

In general, the more experimental bands are involved in the theoretical calculation, the more reliable it is for the assignment of the AC.¹⁰⁶ Thus, the 60 lowest energies for the studied compounds were calculated at the TDB3LYP/6-31+G(d) level, which covers the range of experimental measurement (Table S4†). The calculated absorption wavelengths, oscillator strengths, and major contributions of the studied compounds, compared to the experimental values, are summarized in Tables 1 and S5.† The simulated UV-Vis/CD spectra are shown in Fig. 2 along with the experimental spectra. Notably, the simulated UV-Vis/CD spectra are in reasonably good agreement with the experimental spectra, not only for the relative peak intensities but also for the band positions. Moreover, the values of the rotational strengths calculated using the length and velocity gauge representation of the electric dipole operator are close to each other (Table S4, ESI†). Thus, our adopted method can reliably describe the electron transition properties and assign the ACs of the quinoxaline-fused [7]carbohelicene derivatives with high confidence. The CD spectra may be sensitive to the solvent.¹⁰⁷ The geometries of the studied compounds were re-optimized to test the influence of THF solvent under the PCM model. Next, their solution UV-Vis/CD spectra were also re-calculated based on PCM structures (Fig. S2†). It was found that the shape of the solution UV-Vis/CD spectra are nearly same as the gas phase spectra except for a slightly hypsochromic shift. This indicates that the influence of the solvent is negligible for the studied compounds.

Table 1 Computed absorption wavelengths (λ in nm) compared to experimental data (in parentheses), oscillator strengths (f), and major contributions for compound 2 at the B3LYP/6-31+G(d) level of theory

Band	λ	f	Major contribution
Band 1	282.49(276)	0.782	HOMO−4 → LUMO+2 (42%)
			HOMO → LUMO+4 (14%)
Band 2	316.45(332)	0.220	HOMO−6 → LUMO (77%)
			HOMO−4 → LUMO+2 (9%)
Band 3	346.13(366)	0.207	HOMO → LUMO+2 (37%)
			HOMO−1 → LUMO+1 (22%)
Band 4	424.85(427)	0.190	HOMO−1 → LUMO (85%)
			HOMO → LUMO+2 (12%)

---

Fig. 2 Calculated UV-Vis (left) and CD (right) spectra in the gas phase of 1, 2, 3 and 4 at the TDB3LYP/6-31+G(d) level of theory along with the experimental spectra (red dashed line). The data to prepare the experimental spectra were taken from ref. 51.

The molecular orbitals (MO) involved in the main electronic transitions for the studied compounds 1–4 are shown in Fig. 3 and S3,† respectively. Compound 1 ([7]carbohelicene) exhibits an intense absorption band at 274 nm and two relatively weak absorption bands at 312 and 374 nm. Its main electron transition characteristics can be described as π–π*, as characterized by the fact that these orbitals have π symmetry features. However, compound 2 exhibits four main absorption bands (282, 316, 346, and 425 nm). Notably, the main absorption bands of compound 2 are red-shifted compared with those of compound 1, which is also in agreement with the experimental observations.⁵¹ Quinoxaline is an electron–acceptor group.⁵¹ In general, the electron–acceptor group mainly modulates the LUMO energy level. As a consequence, the LUMO energy of compound 2 is much lower than that of compound 1 (Table S6†), which leads to the smaller energy gap (E_g) for compound 2. Moreover, the main electron transition characters are charge transfers from quinoxaline to [7]carbohelicene and vice versa (Fig. 3). On the basis of the above analysis, it was found that incorporation of the quinoxaline unit not only modulates the electron absorption wavelength but also alters the electron transition properties. Compounds 3 and 4 also exhibit four absorption bands which are similar to those of compound 2. In other words, the substituent effects of the phenyl or 4-methoxyphenyl groups on the UV-Vis spectra of compound 2 are not great. It is noted that some of the molecular orbitals involved in these transitions are partially located on the phenyl or 4-methoxyphenyl groups.

Fig. 3 Molecular orbital isosurfaces involved in the main electron transitions of compound 2 at the TDB3LYP/6-31+G(d) level of theory.

Although the CD spectra of quinoxaline-fused [7]carbohelicene derivatives (compounds 2 to 4) are similar to those of [7]carbohelicene (compound 1), there is a slight difference between them. Specifically, compound 1 exhibits a negative Cotton band around 300 nm (labeled as band 2), while this band becomes positive in compounds 2 to 4. This indicates that the CD spectra are sensitive to molecular structures. It should be noted that the calculated relative peak intensities around 300 nm (labeled as band 2) of compounds 1 to 3 are slightly different from the experimental peak intensities. To further understand the chiral origins of the studied compounds, their corresponding molecular orbitals are shown in Fig. S4.† The analysis shows that the chiral origins have a common character for the quinoxaline-fused [7]carbohelicene derivatives (compounds 2 to 4), which can be attributed to the exciton coupling between the quinoxaline, phenyl or 4-methoxyphenyl groups and [7]carbohelicene, which is completely different from those in [7]carbohelicene (Fig. S4†).

3.4. Second-order nonlinear optical response (NLO) properties

Chiral compounds have been viewed as a valuable alternative in the search for new second-order NLO materials due to their intrinsic non-centrosymmetric structures,¹⁰⁸ which allows their NLO effects to be observed even in highly symmetric media.^108,109 Based on the above electronic transition analysis, quinoxaline-fused [7]carbohelicene derivatives (compounds 2 to 4) exhibit intramolecular charge transfer. Thus, the larger intramolecular charge transfer will come into being under the external electron field and a large NLO response can be observed. Strong electron donor (NH₂) or electron acceptor (NO₂) groups were also introduced to probe the charge transfer cooperativity and find an effective way to enhance the NLO response. Recently, DFT calculations have emerged as a powerful tool for the investigation and prediction of compounds with large NLO responses.^110–115 Thus, the first hyperpolarizability (β_HRS) values of the studied compounds were calculated at the CAM-B3LYP/6-31+G(d) level and are given in Table 2. The calculated β_HRS values of these studied compounds are larger than those of the typical organic NLO compounds. For example, the calculated β_HRS value of compound 6 is about 8 times larger than that of the highly π-delocalized phenyliminomethyl ferrocene complex^116,117 and 190 times larger than that of the organic urea molecule.^66,118 Thus, the studied compounds could function as excellent second-order NLO materials. The β_HRS values for compounds 3 to 5 increase as follows: 3 < 4 < 5, which is agreement with the trend of electron donor ability (H < OCH₃ < NH₂). However, compound 6 has the largest β_HRS value among these compounds. Thus, NO₂ as the terminal substitution is an effective way to enhance the NLO response. Electron transition analysis shows that the charge transfer from [7]carbohelicene to the nitrobenzene moieties plays the key role in determining its NLO response. (Fig. S3†). The quinoxaline group in compound 6 acts as a bridge of charge transfer. It is noted that compound 6 has the smallest band gap (Table S6†).

Table 2 The calculated first hyperpolarizability (β_HRS) values (10⁻³⁰ esu) of the studied compounds 3 to 6 at the CAM-B3LYP/6-31+G(d) level of theory

Compound	βHRS
3	4.43
4	10.87
5	20.09
6	32.96

---

3.5. Charge transport properties

Recently, helicene derivatives have exhibited good and unique charge transport abilities,^45,119 which is very important for improving the performance of organic thin-film transistors and organic light emitting diodes. For example, unprecedented carrier inversion has been observed for azaboradibenzo[6]helicene. Its racemate acts as a hole transport material, while the single enantiomer acts as an electron transport material.¹¹⁹ Compounds containing the quinoxaline group exhibit excellent electron transport ability.¹²⁰ Interestingly, quinoxaline-fused [7]carbohelicene derivatives possess unique crystal packing, as discussed in the introduction. Inspired by those, we investigated their charge transport properties using the band model.^121,122 From the viewpoint of the band model, the larger the bandwidth, the larger the carrier mobility.¹²³ It is noted that the spatial distribution of the corresponding wavefunctions is also a factor that influences charge transport properties. Herein, we were mainly concerned with the band model. The calculated band structures of compounds 2 and 4 using the Vienna ab initio simulation package along high-symmetry directions are shown in Fig. 4 and S5.† For compound 2, the bandwidth of the valence band (0.10 eV) is almost equal to that of the conduction band (0.08 eV) and slightly larger than that of tris(8-hydroxyquinolinato)aluminium (AlQ). This finding can also be supported by the frontier molecular orbitals of compound 2. That is, the HOMO is mainly localized on the [7]carbohelicene part, while the LUMO sits on the quinoxaline group (Fig. 3). This is a typical feature for ambipolar charge transport materials.^124,125 Thus, compound 2 can act as an ambipolar charge transport material. Compound 4 forms enantiomer and racemate crystals, respectively. It is found that the racemate crystals favour electron transport, while the enantiomer crystals favour ambipolar charge transport. It should be noted that the charge transport ability of compound 4 is much lower than that of compound 1.

Fig. 4 Calculated band structure of the crystal for compound 2. The high symmetry points are Z = (0, 0, 0.5), A = (0.5, 0.5, 0.5), M = (0.5, 0.5, 0), Γ = (0, 0, 0), Z = (0, 0, 0.5), R = (0, 0.5, 0.5), X = (0, 0.5, 0) and Γ= (0, 0, 0).

4. Conclusion

In this paper, the UV-Vis absorption spectra, CD spectra, charge transport properties, and second-order NLO properties of a series of quinoxaline-fused [7]carbohelicene derivatives were systemically investigated using density functional theory. The calculated UV-Vis/CD spectra are in good agreement with the experimental spectra, which can be used to assign the electron transition properties and ACs with high confidence. Exciton coupling between quinoxaline, phenyl or 4-methoxyphenyl groups and [7]carbohelicene are mainly responsible for the chiroptical origin of the quinoxaline-fused [7]carbohelicene derivatives. The charge transport abilities of the studied compounds are sensitive not only to molecular structure but also to crystal packing. Compound 2 can act as an ambipolar charge transport material. In view of their first hyperpolarizability (β_HRS) values and intrinsic non-centrosymmetric electronic structures, the studied compounds have the potential to be excellent second-order NLO materials.

Acknowledgements

The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (21377021) and the Natural Science Foundation of Jilin Province (20140101045JC and 20150101042JC).

Notes and references

1. H. Ascolani, M. W. van der Meijden, L. J. Cristina, J. E. Gayone, R. M. Kellogg, J. D. Fuhr and M. Lingenfelder, Chem. Commun., 2014, 50, 13907–13909.
2. A. Shchyrba, M. T. Nguyen, C. Wackerlin, S. Martens, S. Nowakowska, T. Ivas, J. Roose, T. Nijs, S. Boz, M. Schar, M. Stohr, C. A. Pignedoli, C. Thilgen, F. Diederich, D. Passerone and T. A. Jung, J. Am. Chem. Soc., 2013, 135, 15270–15273.
3. T. Balandina, M. W. van der Meijden, O. Ivasenko, D. Cornil, J. Cornil, R. Lazzaroni, R. M. Kellogg and S. de Feyter, Chem. Commun., 2013, 49, 2207–2209.
4. N. Saleh, B. Moore II, M. Srebro, N. Vanthuyne, L. Toupet, J. A. Williams, C. Roussel, K. K. Deol, G. Muller, J. Autschbach and J. Crassous, Chem.–Eur. J., 2015, 21, 1673–1681.
5. J. J. Xie, Y. Y. Duan and S. A. Che, Adv. Funct. Mater., 2012, 22, 3784–3792.
6. J. F. Lamère, I. Malfant, A. Sournia-Saquet, P. G. Lacroix, J. M. Fabre, L. Kaboub, T. Abbaz, A.-K. Gouasmia, I. Asselberghs and K. Clays, Chem. Mater., 2007, 19, 805–815.
7. E. Gomar-Nadal, J. Veciana, C. Rovira and D. B. Amabilino, Adv. Mater., 2005, 17, 2095–2098.
8. P. G. Lacroix, Chem. Mater., 2001, 13, 3495–3506.
9. A. Bousseksou, G. B. Molnár and G. Matouzenko, Eur. J. Inorg. Chem., 2004, 2004, 4353–4369.
10. M. J. Fuchter, M. Weimar, X. Yang, D. K. Judge and A. J. P. White, Tetrahedron Lett., 2012, 53, 1108–1111.
11. G. M. Upadhyay, H. R. Talele, S. Sahoo and A. V. Bedekar, Tetrahedron Lett., 2014, 55, 5394–5399.
12. F. Aloui, S. Moussa and B. B. Hassine, Tetrahedron Lett., 2012, 53, 3216–3219.
13. Y. Shen, H. Y. Lu and C. F. Chen, Angew. Chem., Int. Ed., 2014, 53, 4648–4651.
14. A. Ueda, H. Wasa, S. Suzuki, K. Okada, K. Sato, T. Takui and Y. Morita, Angew. Chem., Int. Ed., 2012, 51, 6691–6695.
15. S. M. Mel, M. Srebro, E. Anger, N. Vanthuyne, C. Roussel, C. Lescop, J. Autschbach and J. Crassous, Chirality, 2013, 25, 455–465.
16. M. Gingras, Chem. Soc. Rev., 2013, 42, 968–1006.
17. C. Shen, E. Anger, M. Srebro, N. Vanthuyne, K. K. Deol, T. D. Jefferson Jr, G. Muller, J. A. G. Williams, L. Toupet, C. Roussel, J. Autschbach, R. Reau and J. Crassous, Chem. Sci., 2014, 5, 1915–1927.
18. P. Aillard, A. Voituriez and A. Marinetti, Dalton Trans., 2014, 43, 15263–15278.
19. M. J. Narcis and N. Takenaka, Eur. J. Org. Chem., 2014, 2014, 21–34.
20. N. Takenaka, R. S. Sarangthem and B. Captain, Angew. Chem., Int. Ed., 2008, 47, 9708–9710.
21. K. Soai and I. Sato, Chirality, 2002, 14, 548–554.
22. C. Nuckolls and T. J. Katz, J. Am. Chem. Soc., 1998, 120, 9541–9544.
23. M. T. Reetz and S. Sostmann, Tetrahedron, 2001, 57, 2515–2520.
24. H. Guédouar, F. Aloui, S. Moussa, J. Marrot and B. B. Hassine, Tetrahedron Lett., 2014, 55, 6167–6170.
25. E. Botek, B. Champagne, M. Turki and J. M. Andre, J. Chem. Phys., 2004, 120, 2042–2048.
26. T. Verbiest, S. V. Elshocht, M. Kauranen, L. Hellemans, J. Snauwaert, C. Nuckolls, T. J. Katz and A. Persoons, Science, 1998, 282, 913–915.
27. C. A. Daul, I. Ciofini and V. Weber, Int. J. Quantum Chem., 2003, 91, 297–302.
28. E. Murguly, R. McDonald and N. R. Branda, Org. Lett., 2000, 2, 3169–3172.
29. Z. An and M. Yamaguchi, Chem. Commun., 2012, 48, 7383–7385.
30. S. Honzawa, H. Okubo, S. Anzai, M. Yamaguchi, K. Tsumoto and I. Kumagai, Bioorg. Med. Chem., 2002, 10, 3213–3218.
31. H. Nakagawa, M. Yoshida, Y. Kobori and K.-I. Yamada, Chirality, 2003, 15, 703–708.
32. J. Storch, J. Zadny, T. Strasak, M. Kubala, J. Sykora, M. Dusek, V. Cirkva, P. Matejka, M. Krbal and J. Vacek, Chem.–Eur. J., 2015, 21, 2343–2347.
33. N. Islam and A. H. Pandith, J. Mol. Model., 2014, 20, 2535.
34. R. Hassey, E. J. Swain, N. I. Hammer, D. Venkataraman and M. D. Barnes, Science, 2006, 314, 1437–1439.
35. R. Hassey, K. D. McCarthy, E. Swain, D. Basak, D. Venkataraman and M. D. Barnes, Chirality, 2008, 20, 1039–1046.
36. Y. Zhou, T. Lei, L. Wang, J. Pei, Y. Cao and J. Wang, Adv. Mater., 2010, 22, 1484–1487.
37. M. J. Fuchter, J. Schaefer, D. K. Judge, B. Wardzinski, M. Weimar and I. Krossing, Dalton Trans., 2012, 41, 8238–8241.
38. J. Žádný, P. Velíšek, M. Jakubec, J. Sýkora, V. Církva and J. Storch, Tetrahedron, 2013, 69, 6213–6218.
39. A. Urbano, Angew. Chem., Int. Ed., 2003, 42, 3986–3989.
40. M. C. Carreno, M. G. Lopez and A. Urbano, Chem. Commun., 2005, 611–613.
41. F.-G. Klärner and B. Kahlert, Acc. Chem. Res., 2003, 36, 919–932.
42. T. J. Lahary, D. Jacquemin, B. Legouin, J.-Y. L. Questel, J.-F. Cupif, L. Toupet, P. Uriac and J. Graton, J. Phys. Chem. C, 2015, 119, 3771–3779.
43. M. Lindqvist, K. Borre, K. Axenov, B. Kotai, M. Nieger, M. Leskela, I. Papai and T. Repo, J. Am. Chem. Soc., 2015, 137, 4038–4041.
44. Y. L. Si and G. C. Yang, J. Mater. Chem. C, 2013, 1, 2354–2361.
45. C. Kim, T. J. Marks, A. Facchetti, M. Schiavo, A. Bossi, S. Maiorana, E. Licandro, F. Todescato, S. Toffanin, M. Muccini, C. Graiff and A. Tiripicchio, Org. Electron., 2009, 10, 1511–1520.
46. L. Q. Shi, Z. Liu, G. F. Dong, L. Duan, Y. Qiu, J. Jia, W. Guo, D. Zhao, D. L. Cui and X. T. Tao, Chem.–Eur. J., 2012, 18, 8092–8099.
47. M. Monteforte, S. Cauteruccio, S. Maiorana, T. Benincori, A. Forni, L. Raimondi, C. Graiff, A. Tiripicchio, G. R. Stephenson and E. Licandro, Eur. J. Org. Chem., 2011, 2011, 5649–5658.
48. S. Maiorana, A. Papagni, E. Licandro, R. Annunziata, P. Paravidino, D. Perdicchia, C. Giannini, M. Bencini, K. Clays and A. Persoons, Tetrahedron, 2003, 59, 6481–6488.
49. M. H. Garcia, P. Florindo, M. D. F. M. Piedade, S. Maiorana and E. Licandro, Polyhedron, 2009, 28, 621–629.
50. H.-J. Son, W.-S. Han, D.-H. Yoo, K.-T. Min, S.-N. Kwon, J. Ko and S. O. Kang, J. Org. Chem., 2009, 74, 3175–3178.
51. H. Sakai, S. Shinto, Y. Araki, T. Wada, T. Sakanoue, T. Takenobu and T. Hasobe, Chem.–Eur. J., 2014, 20, 10099–10109.
52. K.-T. Lin, H.-M. Kuo, H.-S. Sheu and C. K. Lai, Tetrahedron, 2014, 70, 6457–6466.
53. A. D. Becke, J. Chem. Phys., 1993, 98, 5648.
54. M. Caricato, G. W. Trucks and M. J. Frisch, J. Chem. Theory Comput., 2010, 6, 1966–1970.
55. C.-G. Liu, X.-H. Guan and Z.-M. Su, J. Phys. Chem. C, 2011, 115, 6024–6032.
56. S. Grimme and S. D. Peyerimhoff, Chem. Phys., 1996, 204, 411–417.
57. P. A. Brooksby and W. R. Fawcett, Spectrochim. Acta, Part A, 2001, 57, 1207–1221.
58. C. Bernini, L. Zani, M. Calamante, G. Reginato, A. Mordini, M. Taddei, R. Basosi and A. Sinicropi, J. Chem. Theory Comput., 2014, 10, 3925–3933.
59. C. J. Cramer and D. G. Truhlar, Chem. Rev., 1999, 99, 2161–2200.
60. F. Mançois, L. Sanguinet, J.-L. Pozzo, M. Guillaume, B. Champagne, V. Rodriguez, F. Adamietz, L. Ducasse and F. Castet, J. Phys. Chem. B, 2007, 111, 9795–9802.
61. A. Plaquet, M. Guillaume, B. Champagne, F. Castet, L. Ducasse, J.-L. Pozzo and V. Rodriguez, Phys. Chem. Chem. Phys., 2008, 10, 6223–6232.
62. R. Bersohn, J. Chem. Phys., 1966, 45, 3184.
63. G. Kresse and J. Furthmüller, Phys. Rev. B: Condens. Matter Mater. Phys., 1996, 54, 11169–11186.
64. G. Kresse and J. Hafner, Phys. Rev. B: Condens. Matter Mater. Phys., 1993, 48, 13115–13118.
65. Y. L. Si, G. C. Yang and Z. M. Su, J. Mater. Chem. C, 2013, 1, 1399.
66. Y. L. Si and G. C. Yang, J. Phys. Chem. A, 2014, 118, 1094–1102.
67. Y. M. Sang, L. K. Yan, N. N. Ma, J. P. Wang and Z. M. Su, J. Phys. Chem. A, 2013, 117, 2492–2498.
68. Y. L. Si and G. C. Yang, RSC Adv., 2013, 3, 2241–2247.
69. Y. M. Sang, L. K. Yan, J. P. Wang and Z. M. Su, J. Phys. Chem. A, 2012, 116, 4152–4158.
70. H. Lee, S. Cheon and M. Cho, J. Chem. Phys., 2010, 132, 225102.
71. J. P. Wang, L. K. Yan, G. C. Yang, W. Guan and Z. M. Su, J. Mol. Graphics Modell., 2012, 35, 49–56.
72. I. Valencia, Y. Á. Torres, N. B. Behrens and I. L. Garzón, J. Mol. Struct., 2015, 1085, 52–62.
73. L. Li, B.-B. Yang and Y.-K. Si, Chin. Chem. Lett., 2014, 25, 1586–1590.
74. J. M. Slocik, A. O. Govorov and R. R. Naik, Nano Lett., 2011, 11, 701–705.
75. S. Grimme, J. Harren, A. Sobanski and F. Vögtle, Eur. J. Org. Chem., 1998, 1998, 1491–1509.
76. A. Rauk, D. Yang, D. Tsankov, H. Wieser, Y. Koltypin, A. Gedanken and G. V. Shustov, J. Am. Chem. Soc., 1995, 117, 4160–4166.
77. G. V. Shustov, A. V. Kachanov, G. K. Kadorkina, R. G. Kostyanovskii and A. Rauk, J. Am. Chem. Soc., 1992, 114, 8257–8262.
78. G. V. Shustov, S. V. Varlamov, I. I. Chervin, A. E. Aliev, R. G. Kostyanovskii, D. Kim and A. Rauk, J. Am. Chem. Soc., 1989, 111, 4210–4215.
79. A. E. Hansen and T. D. Bouman, J. Am. Chem. Soc., 1985, 107, 4828–4839.
80. J. M. Sauvage, M. Morcellet and C. Loucheux, Macromolecules, 1984, 17, 452–456.
81. C. R. Legler, N. R. Brown, R. A. Dunbar, M. D. Harness, K. Nguyen, O. Oyewole and W. B. Collier, Spectrochim. Acta, Part A, 2015, 145, 15–24.
82. E. Miliordos and S. S. Xantheas, J. Chem. Phys., 2015, 142, 094311.
83. B. G. Janesko and D. Yaron, J. Chem. Theory Comput., 2005, 1, 267–278.
84. G. I. Csonka, A. Ruzsinszky and J. P. Perdew, J. Phys. Chem. B, 2005, 109, 21471–21475.
85. E. A. Bushnell and R. J. Boyd, J. Phys. Chem. A, 2015, 119, 911–918.
86. E. Geidel and F. Billes, J. Mol. Struct.: THEOCHEM, 2000, 507, 75–87.
87. N. Ramos-Berdullas, I. Perez-Juste, C. van Alsenoy and M. Mandado, Phys. Chem. Chem. Phys., 2015, 17, 575–587.
88. A. Neugebauer and G. Häfelinger, J. Mol. Struct.: THEOCHEM, 2002, 578, 229–247.
89. A. Slimani, X. Yu, A. Muraoka, K. Boukheddaden and K. Yamashita, J. Phys. Chem. A, 2014, 118, 9005–9012.
90. M. D. Wodrich, C. Corminboeuf and P. V. R. Schleyer, Org. Lett., 2006, 8, 3631–3634.
91. C. Lepetit, H. Chermette, M. Gicquel, J.-L. Heully and R. Chauvin, J. Phys. Chem. A, 2007, 111, 136–149.
92. A. Forni, S. Pieraccini, S. Rendine and M. Sironi, J. Comput. Chem., 2014, 35, 386–394.
93. F. Moscardó and A. J. Pérez-Jiménez, Int. J. Quantum Chem., 1998, 67, 143–156.
94. D. Jacquemin and C. Adamo, Int. J. Quantum Chem., 2012, 112, 2135–2141.
95. R. Gayathri and M. Arivazhagan, Spectrochim. Acta, Part A, 2014, 123, 309–326.
96. D. Mahadevan, S. Periandy and S. Ramalingam, Spectrochim. Acta, Part A, 2011, 84, 86–98.
97. N. X. Wang and A. K. Wilson, J. Phys. Chem. A, 2003, 107, 6720–6724.
98. J.-L. Chen, J.-T. Hong, K.-J. Wu and W.-P. Hu, Chem. Phys. Lett., 2009, 468, 307–312.
99. E. G. Hohenstein, S. T. Chill and C. D. Sherrill, J. Chem. Theory Comput., 2008, 4, 1996–2000.
100. B. S. Jursic, J. Mol. Struct.: THEOCHEM, 1998, 432, 211–217.
101. W.-T. Chan, I. P. Hamilton and H. O. Pritchard, J. Chem. Soc., Faraday Trans., 1998, 94, 2303–2306.
102. R. Orlando, V. Lacivita, R. Bast and K. Ruud, J. Chem. Phys., 2010, 132, 244106.
103. S. Tomić and N. M. Harrison, AIP Conf. Proc., 2010, 1199, 65–66.
104. N. Kuritz, T. Stein, R. Baer and L. Kronik, J. Chem. Theory Comput., 2011, 7, 2408–2415.
105. B. M. Wong and T. H. Hsieh, J. Chem. Theory Comput., 2010, 6, 3704–3712.
106. F. Furche and R. Ahlrichs, J. Chem. Phys., 2001, 114, 10362.
107. G. C. Yang, Y. L. Si and Z. M. Su, J. Phys. Chem. A, 2011, 115, 13356–13363.
108. E. Botek, J.-M. André, B. Champagne, T. Verbiest and A. Persoons, J. Chem. Phys., 2005, 122, 234713.
109. M. Kauranen, T. Verbiest and A. Persoons, J. Nonlinear Opt. Phys. Mater., 1999, 08, 171–189.
110. Y. Zhang and B. Champagne, J. Phys. Chem. C, 2012, 116, 21973–21981.
111. A. Mahmood, M. I. Abdullah and M. F. Nazar, Bull. Korean Chem. Soc., 2014, 35, 1391–1396.
112. Y. Z. Li, Y. H. Zhang, D. W. Qi, C. F. Sun and L. P. Yang, J. Mater. Sci.: Mater. Electron., 2014, 25, 5255–5263.
113. F. Castet, A. Pic and B. Champagne, Dyes Pigm., 2014, 110, 256–260.
114. L. J. Zhang, D. D. Qi, L. Y. Zhao, C. Chen, Y. Z. Bian and W. J. Li, J. Phys. Chem. A, 2012, 116, 10249–10256.
115. L.-H. Zhang, Y. Wang, F. Ma and C.-G. Liu, J. Organomet. Chem., 2012, 716, 245–251.
116. G. C. Yang, Y. L. Si and Z. M. Su, Org. Biomol. Chem., 2012, 10, 8418–8425.
117. J. S. Chappell, A. N. Bloch, W. A. Bryden, M. Maxfield, T. O. Poehler and D. O. Cowan, J. Am. Chem. Soc., 1981, 103, 2442–2443.
118. D. R. Kanis, M. A. Ratner and T. J. Marks, Chem. Rev., 1994, 94, 195–242.
119. T. Hatakeyama, S. Hashimoto, T. Oba and M. Nakamura, J. Am. Chem. Soc., 2012, 134, 19600–19603.
120. T. H. Huang, W. T. Whang, J. Y. Shen, Y. S. Wen, J. T. Lin, T. H. Ke, L. Y. Chen and C. C. Wu, Adv. Funct. Mater., 2006, 16, 1449–1456.
121. Y. T. Yang, H. Geng, S. W. Yin, Z. G. Shuai and J. B. Peng, J. Phys. Chem. B, 2006, 110, 3180–3184.
122. J. Widany, G. Daminelli, A. Di Carlo, P. Lugli, G. Jungnickel, M. Elstner and T. Frauenheim, Phys. Rev. B: Condens. Matter Mater. Phys., 2001, 63, 233204.
123. M. C. R. Delgado, E.-G. Kim, D. A. D. S. Filho and J.-L. Bredas, J. Am. Chem. Soc., 2010, 132, 3375–3387.
124. C. L. Li, S. P. Wang, W. P. Chen, J. B. Wei, G. C. Yang, K. Q. Ye, Y. Liu and Y. Wang, Chem. Commun., 2015, 51, 10632–10635.
125. G. C. Yang, Y. Liao, Z. M. Su, H. Y. Zhang and Y. Wang, J. Phys. Chem. A, 2006, 110, 8758–8762.

---

Footnote

† Electronic supplementary information (ESI) available: The simulated UV-Vis spectra and CD spectra for the different functionals; a comparison between the calculated and experimentally measured bond lengths; the calculated excitation energies, oscillator and rotational strengths of the 60 lowest energy electronic excitations; molecular orbitals involved into the main electronic transition. See DOI: 10.1039/c5ra12577d

---