Theoretical study on absorption spectrum for novel thioindigo chromophores

The geometrical structures of a series of thioindigo compounds have been optimized by using ab initio HF and DFT-B3LYP method.Subsequently,Time-dependent density functional theory(TD-DFT) and semi-empirical ZINDO approach have been employed to calculated electronic absorption spectrum of thioindigo.The effect of the change of electron-donating group and the extension of chromophore on the electronic spectrum was investigated,and good results were achieved compared with the experimental data.It was shown that,absorption band of chromophore suffers bathochromic shift when electron-donating capability was increased and minor hypsochromic shift when the chromophore was extended.In addition,the frontier molecular orbital composition was analysed by natural population analysis,which indicated that the main absorption spectrum originate from the π→π*electronic transition among the molecular orbitals.