Excited states of antiaromatic systems 1

Abstract

SINDO1 studies were performed to optimize the geometry of excited states of some antiaromatic molecules. It is discussed how such states can exhibit aromatic character upon suitable electronic excitation. The nodal pattern of the molecular orbitals involved in the electronic excitation are used to invoke bond equilization in excited states. We have investigated singlet and triplet excited states of five-membered rings C 4H 5B, C 5H 5 + and C 5H 4O containing four π electrons and bicyclic systems bicyclo-(1,1,0)-butadiene, bicyclo-(2,2,0)-hexatriene and benzocylobutadiene. It is seen that in bicyclo-(2,2,0)-hexatriene, both the bicylic structure and the 1,4-diradical structure determine the equilibrium geometry.