Computational Study on the Working Mechanism of a Stilbene Light-Driven Molecular Rotary Motor: Sloped Minimal Energy Path and Unidirectional Nonadiabatic Photoisomerization
Computational Study on the Working Mechanism of a Stilbene Light-Driven Molecular Rotary Motor: Sloped Minimal Energy Path and Unidirectional Nonadiabatic Photoisomerization
复制标题
DOI：
10.1021/ja211441n
复制
发表时间：
2012-03-14
影响因子：
15
通讯作者：
Morokuma, Keiji
中科院分区：
文献类型：
--
作者：
Liu, Fengyi;Morokuma, Keiji
利用势能面（PES）研究了几何过度拥挤的手性二苯乙烯光驱动分子旋转马达[(2R,2R)-2,2',7,7'-四甲基-1,1'-双（茚二烯），3]的工作机理。（P，P）-stable-cis -> 4(M，M)-unstable-trans-3和（P，P）-stable-trans ->(M，M)-unstable-cis-3这两个光引发顺式-反式（或E/Z）异构化过程的反应路径已经在CASPT2//CASSCF的理论水平上进行了探索。这两个过程的最小能量反应路径（MEPs）在pps上几乎平行，被一个高反转势垒脊分开。mep有一个非常陡的斜率，它驱动C=C键单向旋转。激发态MEPs上的不对称偏置是由“峡湾”区取代基和苯基部分引起的。整个光异构化反应可以描述为一个三态（1B -> 2A -> 1A）多模机制：被激发到1B态的分子首先穿过一个倾斜的1B/2A缝，然后遵循两个协同扭转反应模式，优先穿过两个2A/1A锥形交叉点之一，到达异构基态产物。
The working mechanism of a geometrically overcrowded, chiral stilbene light-driven molecular rotary motor [(2R,2R)-2,2',7,7'-tetramethyl-1,1'-bis(indanylidene), 3] has been investigated by a potential energy surface (PES) study. The reaction paths of the two photoinitiated cis-trans (or E/Z) isomerization processes, namely, (P,P)-stable-cis -> 4(M,M)-unstable-trans-3 and (P,P)-stable-trans ->(M,M)-unstable-cis-3, have been explored at the CASPT2//CASSCF level of theory. The minimal energy reaction paths (MEPs) of these two processes are nearly parallel on the PESs, separated by a ridge of high inversion barrier. The MEPs have a remarkably steep slope, which drives C=C bond rotation unidirectionally. The asymmetric bias on the excited-state MEPs is caused by the substituents on the "fiord" region as well as by the phenyl moieties. The overall photoisomerization reaction can be described as a three-state (1B -> 2A -> 1A) multimode mechanism: The molecule excited to the 1B state first crosses one of the sloped 1B/2A seams, and then follows two cooperative torsional reaction modes to cross preferentially one of the two 2A/1A conical intersections to reach the isomerized ground-state product.