### 含BN旋转轴的光驱动分子马达的理论设计和机理研究

1. 陕西师范大学化学化工学院 陕西省大分子科学重点实验室 西安 710119
• 投稿日期:2017-11-27 发布日期:2018-01-22
• 通讯作者: 刘峰毅 E-mail:fengyiliu@snnu.edu.cn
• 基金资助:

项目受国家自然科学基金（Nos.21473107，21636006）和中央高校基本科研业务费（No.GK201502002）专项资金资助.

### Theoretical Design and Mechanistic Study on a Light-Driven Molecular Rotary Motor with B=N Axis

Guo Ni, Wang Bin, Liu Fengyi

1. School of Chemistry and Chemical Engineering, Shaanxi Normal University, Key Laboratory for Macromolecular Science of Shaanxi Province, Xi'an 710119, China
• Received:2017-11-27 Published:2018-01-22
• Contact: 10.6023/A17110509 E-mail:fengyiliu@snnu.edu.cn
• Supported by:

Project supported by the National Natural Science Foundation of China (Nos. 21473107, 21636006) and Fundamental Research Funds for the Central Universities (No. GK201502002).

Light-driven molecular motors have attracted overwhelming attention due to their potential applications in a wide range of fields. Despite of the great successes obtained in alkene-based light-driven molecular motors and switches, scientists pursuing high-efficient alternatives with superior working mechanisms have never suspended. In this report, a promising model of light-driven rotary motor, namely BN-stilbene motor, constructed by replacing the central C=C axis of a CC-stilbene rotary motor with a polar B=N bond, was rationally designed. Multireference Complete Active Space Self-Consistent Field (CASSCF) method and Time-Dependent Density Functional (TDDFT) theory were applied to study the mechanism of BN-stilbene, along with the Complete Active Space Second-Order Perturbation Theory (CASPT2) energy corrections. Our calculations show that the B=N axis well preserves the conjugation of between the rotor and stator, leading to four ground-state helical conformers (i.e., cis-stable, trans-unstable, trans-stable and cis-unstable), whose geometries and energies are in line with their counterparts in CC-stilbene motor; in addition, BN-stilbene has similar absorption spectra and more slopped excited-state potential energy curves at Franck-Condon region, which can fascinate a spontaneous rotary motion around B=N axis, thus generates directional photo-induced isomerization from cis-stable to trans-unstable (or from trans-stable to cis-unstable). Moreover, the barriers for helical inversions (trans-unstable → trans-stable or cis-unstable → cis-stable) are found to be lower than those of the reversed thermal rotations (i.e., cis-stable → trans-unstable and trans-stable → cis-unstable), which further insures the unidirectionality of rotation. These features sufficiently allow BN-stilbene to serve as a candidate for light-driven molecular rotary motor. Finally and most importantly, as compared with that of CC-stilbene, the photoisomerization mechanism of BN-stilbene motor shows advantages in nonadiabatic transition:Due to the introducing of polar B=N axis, the S1/S0 conical intersections of BN system are both geometrically and energetically closer to the excited-state intermediate, which is thus expected to improve the nonadiabatic transition probabilities and the unidirectionality of the rotation. Therefore, the BN-stilbene motor is expected to perform a unidirectional, repetitive 360° rotation upon sequential applying of photo and thermal inputs. The findings suggest BN-hetero stilbene as a promising type of light-driven rotary motor and may inspire the design and synthesis of novel molecular motors.