π-共轭分子中激发态的对称性与暗态的起源  

Excitation Symmetry and Origin of Dark States in π-Conjugated Molecules

作　　者：谢军 盛卫东 Jun Xie;Weidong Sheng(State Key Laboratory of Surface Physics and Department of Physics,Fudan University,Shanghai 200433,China)

机构地区：[1]复旦大学物理系,表面物理国家重点实验室,上海200433

出　　处：《Chinese Journal of Chemical Physics》2023年第3期307-312,I0100,共7页化学物理学报（英文）

摘　　要：本文利用严格对角化方法研究了处于不同介电环境中两种典型的π共轭单分子蒽和菲的光吸收谱.对于具有不对称几何形状的受限量子体系,人们普遍认为系统的第一激发态应该局限于结构的长轴方向上.同时,偶极近似指向这些局限于长轴方向上激发态的跃迁通常会拥有更强的峰值.本文指出上述两条常识对于蒽和菲这两种分子是不适用的.对于蒽,发现了其吸收谱中第一个亮峰对应的跃迁总是沿着分子的短轴方向.对于菲,同样观察到其吸收谱中峰值最高的谱线的极化方向也是沿着分子的短轴方向.另外,不论是蒽还是菲,其第一激发态在某些介电环境中不会出现在吸收谱当中,即成为了光学暗态.经过仔细考察体系能级随各种参数的变化关系,最终确定这些暗态的形成可以归结于分子中的短程库伦相互作用.Utilizing the exact diagonalization method,the optical absorption spectra of twoπ-conjugated molecules,anthracene and pyrene,are calculated in various dielectric environments.In a confined quantum system with an anisotropic geometry,it is commonly believed that the first excited state is localized along the elongated direction.In the meantime,the dipole approximation says that the transitions to those states localized along the elongated direction shall generally have higher intensities.In this work we report that anthracene and pyrene would respectively fail these intuitive expectations.It is found that the first active transition in anthracene is always polarized along its short axis direction.For pyrene,it is revealed that the transition of the highest intensity is the one polarized along the short axis direction of the molecule.Furthermore,the first excited state in either anthracene or pyrene is often found to be optically inactive,which is successfully attributed to the short-range interactions by examining the energy spectra in varying interaction environments.

关 键 词：激发态的对称性 光吸收 光学暗态 严格对角化 

分 类 号：O43[机械工程—光学工程]