Key Laboratory for Macromolecular Science of Shaanxi Province, School of Chemistry & Chemical Engineering, Shaanxi Normal University, Xi'an, Shaanxi, 710119, P.R. China.
Chemistry. 2019 Mar 15;25(16):4194-4201. doi: 10.1002/chem.201806152. Epub 2019 Feb 22.
The working mechanism including the photoisomerization and thermal isomerization steps of a chiral N-alkyl imine-based motor synthesized by Lehn et al. are revealed by MS-CASPT2//CASSCF and MS-CASPT2//(TD-)DFT methods. For the photoisomerization process of the imine-based motor, it involves both the bright (π,π*) state and the dark (n,π*) state. In addition, the MECI has similar geometry and energy to the minimum of the S state, which shows that the process is barrierless and keeps the unidirectionality of rotation well; the result confirms the imine-based motor is a good candidate for a light-driven molecular rotary motor. For the thermal isomerization process of the imine-based motor, there are two even isomerization paths: one with the mechanism of the in-plane N inversion, the energy barriers of which are 29.6 kcal mol at MS3-CASPT2//CAM-B3LYP level and 29.2 kcal mol at MS3-CASPT2//CASSCF level; the other with the mechanism of ring inversion of the cycloheptatriene moiety, with energy barriers of 28.1 kcal mol at MS3-CASPT2//CAM-B3LYP level and 18.1 kcal mol at MS3-CASPT2//CASSCF level. According to the structural feature of the stator moiety, the imine molecule can be used as a two-step or a four-step light-driven rotary motor.
勒（Lehn）等人合成的手性 N-烷基亚胺基马达的光异构化和热异构化步骤的工作机制通过 MS-CASPT2//CASSCF 和 MS-CASPT2//(TD-)DFT 方法揭示。对于亚胺基马达的光异构化过程，它涉及到亮（π，π*）态和暗（n，π*）态。此外，MECI 与 S 态的最小值具有相似的几何形状和能量，这表明该过程是无势垒的，并很好地保持了旋转的单向性；该结果证实了亚胺基马达是光驱动分子旋转马达的良好候选者。对于亚胺基马达的热异构化过程，有两种偶极异构化途径：一种是平面内 N 反转机制，其能垒在 MS3-CASPT2//CAM-B3LYP 水平为 29.6 kcal/mol，在 MS3-CASPT2//CASSCF 水平为 29.2 kcal/mol；另一种是环庚三烯部分的环反转机制，其能垒在 MS3-CASPT2//CAM-B3LYP 水平为 28.1 kcal/mol，在 MS3-CASPT2//CASSCF 水平为 18.1 kcal/mol。根据定子部分的结构特征，亚胺分子可用作两步或四步光驱动旋转马达。
