Site dependence of the 1 1A g to 2 1A g transition of all-trans-1,3,5,7-octatetraene

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Abstract
Highly resolved emission and one‐photon fluorescence excitation spectra and fluorescence lifetimes for all‐trans‐1,3,5,7‐octatetraene substituted in a series of n‐alkane crystals maintained at liquid helium temperatures have been measured. In the n‐octane host, the 1 1Ag to 2 1Ag transition is strictly symmetry forbidden: In other hosts, the spectra exhibit both allowed and symmetry forbidden components. While the relative intensity of the allowed (built on the 0–0) and the symmetry forbidden (built on odd symmetry vibrational modes) components of the spectra are sensitive to local perturbations, the energies of the excited 1 1Ag and 1 1Bu states and the vibrational development of the 1 1Ag to 2 1Ag transition are nearly the same in all of the hosts studied. The increase in the allowed component of the spectrum with increasing site perturbation correlates with a decrease in the measured fluorescence lifetime.