基于可逆光过程的新型分子机器的理论设计与机理研究

Light-driven molecular rotary motors have attracted overwhelming attention due to their great successes in applications, meanwhile, the unidirectionality and speed of rotation in their photo-induced rotation steps are far from perfectness due to the intrinsic characters of cis-trans photoisomerization of alkene. The photo-induced rotation around C=C axis obeys a multi-modes mechanism, in which the C=C torsional mode is disturbed by other irrelevant modes; and the nonadiabatic transition is hindered by relatively high-energy conical intersections, which will in turn hurt the unidirectionality and slow down the speed of rotation. Tuning the geometric and electronic structures of conical intersection and rotary path, to make them geometrically close to each other on the potential energy surfaces, is the key in optimizing alkene rotary motors. Nowadays, the commonly-used optimization strategy is modifying the rotor and/or stator moieties so as to put indirect influences on the C=C axis. Herein we propose a new design strategy, that is, to use polar double bonds (such as C=N and B=N bonds, which have similar electronic structure with C=C bond) to build molecular rotary motors and molecular switches, so as to ultimately avoid of the drawbacks in alkene motors and switches. The current strategy is expected to be superior to the commonly-used method and thus to obtain molecular machines with better directionality and higher speed of rotation. Theoretical designs of imine and azaborine rotary motors and switches on the base of high-level, multireference quantum chemistry calculations and nonadiabatic molecular dynamic simulations are going to be carried out, and the results are expected to provide theoretical references for further experimental and theoretical researches.

光驱动分子转动马达因其空前成功而得到广泛认可，但由于作为旋转轴的C=C键的光异构化过程自身特性的制约，其运转模式和效率仍有待改进。为解决非极性C=C键旋转中存在的调控锥形交叉与旋转路径的电子结构不同而导致前者偏离旋转路径且能量偏高的问题，传统上多采取修饰定子或转子、间接极化C=C轴来提高马达转速和改善旋转单向性。本项目一改修饰定子或转子而忽视转轴本身的传统思路，提出用极性双键（如C=N和B=N键等与C=C具有相似电子结构的双键）为转轴来设计新型分子马达和分子开关的策略。与传统方法相比，极性转轴的引入能够以更直接、有效的方式调控锥形交叉和旋转路径的电子结构，减小甚至消除二者的几何结构和能量差异，从而有望设计具有纯旋转模式和高转速的分子马达。本项目的基于大规模多参考态方法计算和非绝热动力学模拟的分子设计对光驱动分子机器理论和实验研究具有指导意义。

光驱动分子转动马达因其空前成功而得到广泛认可，但由于作为旋转轴的C=C键的光异构化过程自身特性的制约，其运转模式和效率仍有待改进。本项目致力于探索以区别于C=C双键的极性共价双键为转轴的光驱动分子马达和分子开关的工作机理，为设计具有纯旋转模式和高转速的分子机器建立理论基础；在此基础上开展分子设计和优化，为分子马达的实验研究提供理论支撑和指导。.(1)系统研究了含C=N极性双键的亚胺分子马达和开关体系的工作机理，获得了其基态和激发态高精度势能面，明确了其非绝热化学反应路径，发现了影响光异构化过程的关键因素，分析了基态和激发态间圆锥交叉区域的几何特征与光异构过程的关联；通过与多烯分子马达的对比，确认了亚胺马达在光异构化步骤在单向性和转速上优于多烯马达的推测，并得到了非绝热动力学模拟的验证，为含极性共价键转轴的分子马达的设计、优化和应用提供了理论支撑。.(2)在研究亚胺光异构化体系的同时，针对亚胺存在的稳定性不高、N原子端结合位点少的缺陷，发现了具有显著优于亚胺的光、热稳定性的含C=N-N单元的腙类体系，结合分子内氢键等作用模式，该类体系可以实现丰富多样的结构设计。通过对苯腙（C=N-N）和嗪类（C=N-N=C）体系的多参考态计算表明，该类分子的光异构化为N-N键辅助的C=N旋转模式，且很好继承了亚胺体系光异构化旋转无势垒、单向性好的优点，可作为分子马达和开关应用的良好模型。.(3)研究还发现，C=C、C=N键的光致旋转和分子内氢键等作用的相互影响可以产生多样的应用。在不同体系中，分子内氢键可分别起到抑制和促进双键旋转、或产生与之竞争的ESIPT过程的作用，通过调节质子供受体的电负性，可能实现更为丰富的分子开关和马达的应用。.以上研究不仅能够促进分子马达领域的深入研究和应用，同时对分子和复杂体系的电子激发态研究提供了理论借鉴，具有重要的科学意义。.