Department of Applied Chemistry, Faculty of Engineering, Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan.
Phys Chem Chem Phys. 2021 Jan 21;23(2):1317-1324. doi: 10.1039/d0cp04246c.
An approach to quantitatively analyze the factors contributing to the activation of aggregation-induced emission (AIE) of a molecule is proposed using molecular simulations. A cyanostilbene derivative, 1-cyano-1,2-bis-(4'-methylbiphenyl)ethylene (CN-MBE), has two isomers, E and Z forms. The E-form of CN-MBE exhibits AIE, and is non-emissive in dilute solutions but becomes highly emissive in aggregated states. The Z-form is non-emissive, even in the solid state, that is, the E-form of CN-MBE is AIE-active, while its Z-form is AIE-inactive. In this study, the free energy profiles of the AIE processes of the E and Z forms of CN-MBE are investigated using the free energy perturbation method at the quantum mechanics/molecular mechanics level. The free energy profiles reveal significant differences in the extent to which steric hindrance from surrounding molecules restricts the intramolecular motions of the E and Z forms in the aggregated states. The structural features of the E and Z forms are characterized based on the conformational changes in the excited state relaxation process to reach the conical intersections and the free volume space around the molecules in the aggregated states. This study determines the contributing factors that cause the AIE activity of the molecule by identifying characteristic differences in the free energy profiles of the AIE processes of the AIE-active E-form of CN-MBE and the inactive Z-form. The approach used in this study can be applied to the rational design of highly efficient AIE luminogens utilizing computer modeling.
提出了一种使用分子模拟定量分析导致分子聚集诱导发射（AIE）激活的因素的方法。一种氰基二苯乙烯衍生物，1-氰基-1,2-双（4'-甲基联苯）乙烯（CN-MBE），具有两种异构体，E 型和 Z 型。CN-MBE 的 E 型表现出 AIE，在稀溶液中不发光，但在聚集态下变得高度发光。Z 型是不发光的，即使在固态下也是如此，也就是说，CN-MBE 的 E 型是 AIE 活性的，而其 Z 型是 AIE 非活性的。在这项研究中，使用量子力学/分子力学水平的自由能微扰法研究了 CN-MBE 的 E 和 Z 型的 AIE 过程的自由能曲线。自由能曲线揭示了在聚集态下，周围分子的空间位阻对 E 和 Z 型分子的分子内运动的限制程度存在显著差异。根据在激发态松弛过程中达到锥形交叉和聚集态分子周围自由体积空间的构象变化，对 E 和 Z 型的结构特征进行了表征。本研究通过确定 AIE 活性的 E 型 CN-MBE 和非活性的 Z 型 CN-MBE 的 AIE 过程的自由能曲线的特征差异，确定了导致分子 AIE 活性的因素。本研究中使用的方法可以应用于利用计算机建模对高效 AIE 发光体的合理设计。
