Excited electronic states of dehydro[18]annulene and dehydrobenzo[18]annulene

Electronic absorption and florescence spectra of dehydro[18]annulene and dehydrobenzo[18]annulene have been predicted with the singlet-excitation configuration interaction method. Four electronic absorption bands observed in the experiments have been assigned to electronic transitions. With the application of the Kasha's rule, three florescence peaks of dehydrobenzo[18]annulene observed in experiment have been assigned to electronic transitions of different distortional excited states. The Jahn-Teller effect leads to the excited-state distortions, and the distortional excited state with the large oscillator strength is responsible for the strong multiple florescences.