Yanling Si

Theoretical Study on the Chiroptical Optical Properties of Chiral Fullerene C60 Derivative

Time-dependent density functional theory (TDDFT) calculations have been used to investigate UV/CD spectra and nonlinear optical (NLO) property of the C(60)-fullerene bisadduct (R,R,(f,s)A)-[CD(+)280] for the first time. The electron transition natures of the four main measured bands are analyzed, and their results are used to designate the excited states involved in an electron-transfer process of the studied compound. On a comparative scale, the predicted excitation energies and oscillator strengths are in reasonable agreement with the observed values, demonstrating the efficiency of TDDFT in predicting the localized and charge transfer transitions. The good agreement between the experimental and the simulated CD spectra shows that TDDFT calculations can be used to assign the absolute configurations (ACs) of chiral fullerene C(60) derivatives with high confidence. The observed large dissymmetry ratio g (g = Δε/ε) at about 700 nm results from the orbital characters of the local fullerene excited state, which leads to large transition magnetic dipole moment and small transition electronic dipole moment. The different functionals and solvent effects on UV/CD spectra were also considered. The studied compound has a possibility to be an excellent second-order NLO material from the standpoint of transparency and large second-order polarizability value.

Photophysical properties of azaboradibenzo[6]helicene derivatives

The electronic circular dichroism (CD), UV-Vis absorption and emission spectra, charge transport, and nonlinear optical properties of the novel azaboradibenzo[6]helicene have been investigated by density functional theory (DFT) for the first time. The calculated absorption and emission energies are in good agreement with the experimental ones. The simulated CD spectra nicely reproduce the experimental CD spectra in both excitation energy and rotational strength without any shift or scaling, which can be used to assign its absolute configuration (AC) with high confidence. The electronic transition properties have been assigned and analyzed. The observed CD bands mainly result from exciton-coupling of the ortho-fused aromatic rings. The adiabatic potential energy surface method was used to calculate reorganization energy of the studied compound. The hole reorganization energy is slightly smaller than that of the electron reorganization energy. The largest bond-length changes upon reduction and oxidation are mainly localized on the rings containing B–N bonds. It is found that the photophysical properties of azaboradibenzo[6]helicene can be effectively tuned upon substitution. In view of the second-order polarizability value and intrinsic non-centrosymmetric electronic structure, the studied compounds have the possibility to be excellent second-order nonlinear optical materials.

Chiroptical, linear, and second-order nonlinear optical properties of tetrathiafulvalenylallene: a multifunctional molecular material

Time-dependent density functional theory (TDDFT) calculations have been used to investigate chiroptical, linear, and second-order nonlinear optical (NLO) properties of the novel tetrathiafulvalenylallene in both neutral and two cationic states for the first time. The calculated UV-Vis/ECD spectra of the studied compound are in good agreement with the experimental ones, which can be used to assign its absolute configuration (AC) with high confidence. From neutral state to the two cationic states, the studied compound exhibits pronounced different chiroptical effects and second-order NLO response values. For example, the calculated β0 value of 12+ is 10.36 times as large as that of 1, while the β0 value of 14+ is 46.51 times as large as that of 1. These effects mainly result from the structural modifications of TTF units in the redox process. It is found that charge transfer between the tetrathiafulvalene (TTF) unit and the allene framework plays a key role in determining the chiroptical properties and electronic transition properties. It is interesting to find that the two benzene rings have vanishingly small effects on the chiroptical properties. The studied compound could act as both a chiroptical switch and NLO switch material from the standpoint of different chiroptical and NLO responses, reversible redox processes, and high stability. The effects of different functionals and basis sets, including solvent effects on the UV-Vis/ECD spectra were also considered.

Nonplanar donor-acceptor chiral molecules with large second-order optical nonlinearities: 1,1,4,4-tetracyanobuta-1,3-diene derivatives.

We have investigated the chiroptical, linear, and second-order nonlinear optical (NLO) properties of five 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) derivatives and elucidated structure-property relationships from the micromechanism. The experimental UV-vis absorption and circular dichroism (CD) spectra were well reproduced by our calculations at TDB3LYP/6-31+G* level of theory. The electron transition property and chiroptical origin have been assigned and analyzed. The results show that the studied compounds possess large molecular first hyperpolarizabilities, especially for compound 5 which has a value of 35 × 10(-30) esu, which is comparable with the measured value for highly π-delocalized phenyliminomethyl ferrocene complex and about 200 times larger than the average first hyperpolarizability of the organic urea molecule. Despite the nonplanarity of these compounds, efficient intramolecular charge transfer (CT) from electron donor to electron acceptor moieties was observed, which plays the key role in determining the NLO response. The intramolecular charge transfer cooperativity was also probed. In view of the first hyperpolarizability values, intrinsic noncentrosymmetric electronic structure, and high stability, the studied compounds have the possibility to be excellent second-order NLO materials.

Theoretical study on the photophysical properties of chiral mononuclear and dinuclear zinc complexes

The chiroptical, linear, and second-order nonlinear optical (NLO) properties of chiral mononuclear and dinuclear zinc complexes have been investigated for the first time at density functional theory level. The calculated electron absorption energies and oscillator strengths are in reasonable agreement with the experimental ones. The good agreement between the experimental and the simulated CD spectra shows that TDDFT calculations can be used to assign the absolute configurations (ACs) of chiral zinc complexes with high confidence. Based on these calculated results, the electron transition property and chiroptical origin have been analyzed and assigned. The results show that the coordinated Zn atoms have certain effects on the chiroptical property. The larger nonlinear optical response mainly results from interligand and intraligand charge transfer. The studied complexes have a possibility to be excellent second-order nonlinear optical material from the standpoint of first hyperpolarizability value, transparency and intrinsic non-centrosymmetric electronic structure.

Photophysical properties of quinoxaline-fused [7]carbohelicene derivatives

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 βHRS 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.

Computational study of chiral molecules with high intrinsic hyperpolarizabilities

We have investigated the electronic transition, chiroptical properties, and the second-order nonlinear optical (NLO) properties of eight novel chiral diborate compounds and elucidated structure–property relationships from the micromechanism. These compounds show calculated first hyperpolarizabilities (β) ranging from 2738.52 to 83976.45u2009×u200910−33u2009esu, which means that subtle structural modifications can substantially enhance the first hyperpolarizability. The cooperativity of intramolecular charge transfer and an effective way to enhance the NLO response were also systemically investigated. The linear correlation between the first hyperpolarizability and the inverse of the electronic transition energy suggests that the electronic transition energy plays a key role in determining the NLO response. These compounds have the potential to be excellent second-order NLO materials from the standpoint of the large β values, high transparency and the intrinsic non-centrosymmetry. The electronic transition and chiroptical properties have been assigned and analysed. The main UV–visible absorption features are best described as πu2009→u2009π* transitions. Moreover, the effects of different functionals and basis sets on the first hyperpolarizability were investigated.

Understanding photophysical properties of chiral conjugated corrals for organic photovoltaics

Recently, a chiral conjugated macrocyclic compound containing alternately arranged donor and acceptor motifs exhibited unique advantages (i.e. high absorption coefficient, broad absorption range, and high electron mobility) in organic photovoltaics (OPVs). Understanding the structure–property relationship at the microscopic level is a prerequisite for further performance optimization or improvement. Here, we employed time-dependent density functional theory (TDDFT) to investigate the electronic circular dichroism (CD), UV-vis absorption, charge transport, and second-order nonlinear optical (NLO) properties of the four chiral compounds. The experimental UV-vis/CD spectra of compound 1 were well reproduced by our calculations and could be used to assign the electron transition properties and absolute configuration (AC) with high confidence. The electronic absorption spectra, charge transport properties, and open circuit voltage of compound 1 in OPVs have been rationalized by comparing cyclic and acyclic structures. The designed compounds 2–3 are expected to exhibit excellent performances in OPVs in view of their small energy gaps, large oscillator strengths, and smaller electron reorganization energies. Moreover, the first hyperpolarizability (βtot) of compound 4 is 27 times larger than that of P-nitroaniline. Thus, our studied compounds are also excellent candidates for second-order NLO materials.

Theoretical study on thiophene-based double helicenes with intrinsic large second-order nonlinear optical response

Helicenes have attracted great attention due to their inherent chirality and distinctive optical features. Moreover, the intrinsic chirality of helicene can meet non-centrosymmetric electronic structure requirements of second-order optical materials. Thiophene or polythiophene plays an important role in organic photoelectric materials. For organic molecular materials, several electronic behaviors could be combined into a single molecular entity. By utilizing density functional theory calculations, we here for the first time investigated the electronic structures and optical properties of thiophene-based double helicenes. The calculated electronic excitation energies are in good agreement with the experimental ones. The simulated ECD spectra nicely reproduce the experimental ECD spectra in both excitation energy and rotational strength, which can be used to assign the absolute configurations of thiophene-based double helicenes with high confidence. The electronic transition properties and chiroptical origins have been assigned and analyzed. The studied compounds possess remarkably large molecular first hyperpolarizabilities, especially compound a-5 which has a value of 29.09 × 10−30 esu, which is about 300 times larger than the first hyperpolarizabilities of an organic urea molecule and 7 times larger than that measured for a highly π-delocalized phenyliminomethyl ferrocene complex. The effect of single/double helicenes on first hyperpolarizabilities is compared and discussed. We also probed the intramolecular charge transfer cooperativity, which is important for further experimental investigation. Based on the intrinsic non-centrosymmetric electronic structures, high transparency, and the larger first hyperpolarizability values, the studied compounds are expected to be excellent second-order nonlinear optical materials.

Theoretical study on the photophysical properties of boron-fused double helicenes

Heterohelicenes have attracted much attention because the involvement of heteroatom into helicene skeleton effectively modulates physical properties and greatly widens the application of helicenes. Recently, boron-fused double helicenes (compounds 1 and 2), exhibiting unique photophysical properties, were reported [J. Am. Chem. Soc., 2016, 138, 5210]. Fully understanding their microelectronic structures is rather important for further performance optimization or improvement. Here, we employed density functional theory to investigate the electronic transition properties, circular dichroism (CD), charge transport, and second-order nonlinear optical (NLO) response of the seven boron-fused double helicenes. Our simulated UV-vis/CD spectra of compound 2 are in good agreement with experimental ones. Different electron-donor or electron-acceptor substituents have considerable effect on frontier molecular orbital energy level, absorption wavelength, electron transition property, and second-order NLO response values. The designed compound 7 with two electron donors (TTF) and two electron acceptors (TCNQ) is expected to be excellent second-order NLO material in view of large first hyperpolarizability value and inherent asymmetric structure. The study of charge transport indicates that incorporation boron and oxygen atoms into intermolecular π–π packing units is an effective way to realize ambipolar charge transport.