Changes in the electronic structures of trans-polyenes in the 1 1Ag and 2 1Ag states induced by molecular vibrations

The potential energy curves and changes in electronic structures along a coordinate consisting of CC stretching and C-C shrinking are examined for the 1 1Ag and 2 1Ag states of trans-polyenes ranging from hexatriene to dodecahexaene by the ab initio molecular orbital method. The shapes of the calculated potential energy curves of the 1 1Ag state indicate that they evolve into the double-minimum potential energy curve for trans-polyacetylene. It is likely the character of the 2 1Ag state in a short polyene is transferred to one of the potential energy minima in the 1 1Ag state of a long polyene.