Absorption and emission of 2,12-dimethyltridecahexaene

Abstract

We have obtained well resolved optical spectra of a simple, methyl substituted hexaene at 4.2 K. These spectra provide detailed information on the vibronic levels associated with the ground (1 1Ag) and first excited (2 1Ag) singlet electronic states. The strongest vibronic feature, due to a totally symmetric CC double bond stretch, shifts from 1576 cm−1 in the 1 1Ag state to 1779 cm−1 in the 2 1Ag state. This shift, not accounted for by current theoretical descriptions of polyene electronic states at the crude adiabatic level, may be rationalized as a manifestation of vibronic coupling between the ground and first excited singlet states.