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 ¹A_g) and first excited (2 ¹A_g) singlet electronic states. The strongest vibronic feature, due to a totally symmetric CC double bond stretch, shifts from 1576 cm⁻¹ in the 1 ¹A_g state to 1779 cm⁻¹ in the 2 ¹A_g 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.