摘要
本文利用飞秒受激拉曼光谱结合量子化学计算研究了9-(2,2-二氰乙烯基)久洛啶分子在环已烷、四氢呋喃和二甲基亚砜溶剂中的激发态结构动力学.实验中观测到该分子的氢原子离面振动模式以及双基(C=N)对称/反对称伸缩振动模式,这两种振动模式的发现意味着该分子在光激发后将沿C7=Cg双键和C4-C7单键进行扭转,即通过异构化和分子内扭转电荷转移两种无辐射弛豫方式有效地淬灭局域性激发态上的粒子数.在非极性溶剂中,光激发导致局域性激发态的粒子数布居,其中一部分粒子数通过异构化以无辐射形式弛豫回基态;此外,虽然非极性溶剂中没有出现分子内电荷传中间态,部分局域性激发态粒子数直接通过荧光发射弛豫回到基态,另一部分局域性激发态粒子数则通过分子内扭转电荷转移过程无辐射弛豫回基态.在极性溶剂中,光激发导致局域性激发态粒子数布居,其中一部分粒子数通过异构化无辐射弛豫回基态;另一部分局域性激发态的粒子数通过超快的分子内电荷传递过程弛豫至分子内电荷传递发光态,分子内电荷传递态上的粒子数一部分通过荧光发射弛豫回到基态,另一部分则通过分子内扭转电荷转移过程以无辐射形式弛豫到分子内电荷传递暗态。
Understanding the mechanism of how micro-environments affect molecular rotors helps the design and development of molecular sensors.Here,we utilized femtosecondstimulated Raman spectroscopy,helped by quantum chemical calculation,to study the structural dynamics of 9-(2,2-dicyanovinyl)julolidine in cyclohexane,THF,and DMSO solvents.The obtained hydrogen out-of-plane(HOOP)mode and symmetric/anti-symmetric stretching of two nitriles(C=N)indicate the rotation of the C7=Cg double bond and C4-C7 single bond in the excited-state which provide two non-radiative decay channels to effectively quench the excited-state population on local excited(LE)state via isomerization and twisted intramolecular charge transfer(TICT).In nonpolar solvent,the excited molecule in the LE state radiatively relaxes to the ground state or performs rotation motions via isomerization and TICT to deactivate fluorescence in the LE state.In the polar solvent,the isomerization plays a role to quench the LE state population;simultaneously,an ultrafast intramolecular charge transfer(ICT)from LE state to emissive ICT state was followed by an TICT between ICT state and dark ICT'state.
作者
王正心
姜甲明
黄逸凡
刘伟民
Zhengxin Wang;Jiaming Jiang;Yifan Huang;Weimin Liu(School of Physical Science and Technology,ShanghaiTech University,Shanghai 201210,China)
基金
supported by the Natural Science Foundation of Shanghai(20ZR1436300)
the National Natural Science Foundation of China(No.21872094).
关键词
飞秒受激拉曼光谱
分子内扭转电荷转移
异构化
氢原子离面振动模式
Femtosecond stimulated Raman spectroscopy
Twisted intralomecular charge transfer
Isomerization
Hydrogen out-of plane mode
