Site dependence of the 1thinsp;1Agto 2thinsp;1Agtransition of allhyphen;transhyphen;1,3,5,7hyphen;octatetraene@fa@f)

摘要

Highly resolved emission and onehyphen;photon fluorescence excitation spectra and fluorescence lifetimes for allhyphen;transhyphen;1,3,5,7hyphen;octatetraene substituted in a series ofnhyphen;alkane crystals maintained at liquid helium temperatures have been measured. In thenhyphen;octane host, the 1thinsp;1Agto 2thinsp;1Agtransition 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 0ndash;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 1thinsp;1Agand 1thinsp;1Bustates and the vibrational development of the 1thinsp;1Agto 2thinsp;1Agtransition 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.