Electronic Structures and Optical Properties of Indolocarbazole Isomers

Abstract

Density functional theory(DFT) and the configuration interaction with single excitations(CIS) method were used to optimize the ground state and excited state structures of five indolocarbazole molecules using the 6-31G(d,p) basis set.Based on their geometric structures,the absorption and emission spectra were calculated using time-dependent DFT(TD-DFT) with the same basis set and employing the polarizable continuum medium model(PCM).There are obvious differences in the emission spectra of these isomers as isomer 5 has larger oscillator strength in its emission spectrum,but its transition energies are the lowest among the isomers.The emission peak value of isomer 4 is the highest and the oscillator strengths of isomer 2 are the weakest from 250 to 450 nm.This is because the structures change from ground state to the excited state and the molecular orbital(MO) energy levels of these molecules are different.We also evaluated the nonlinear optical response(first hyperpolarizability) of this series of molecules.The calculated polarizabilities are similar but the static first hyperpolarizabilities(β0) are different.The β0 of isomer 2 is the largest among the compounds investigated.