Theoretical study on geometric electronic structures and absorption wavelengths of closed-ring isomers of diarylmaleic anhydrides

The ground-state geometric structures of six closed-ring isomers of diarylmaleic anhydrides have been fully optimized using density functional theory (DFT) at B3LYP/6-31G(d) level. The specific effect on molecular geometric and electronic structures derived from different aryl (indolyl and thienyl) rings or substituents are investigated in detail. In virtue of time-dependent density functional theory (TD-DFT), the low-lying excited states of various closed-ring isomers are determined using three different density functionals at the same 6-31G(d) basis sets. The calculations show that using TD-B3LYP/6-31G(d) approach, experimental absorption spectrum have been better reproduced with the absolute error ca 10-22 nm (except for molecule 4) in this paper. It has been concluded that the lowest singlet excited state (S1) of these compounds is mainly derived from the HOMO → LUMO (π → π∗) electron transition.