Photochemical isomerization in the absence of a potential barrier: origin of wavelength-dependent ground-state recovery kinetics

Abstract

The photophysics and isomerization dynamics in the excited state of the molecule 1,1′-diethyl-4,4′-cyanine have been investigated. Earlier studies have indicated that the isomerization of this molecule is of the barrierless type. As such, it displays some interesting properties of the excited-state relaxation dynamics. In the present work, we investigate in detail the wavelength dependence of the observed ground-state recovery lifetimes, and show that this dependence is due to a dependence on the analyzing wavelength. We believe that the origin of the effect is the admixture of non-exponential fluorescence-decay components into the ground-state recovery signal. This results in apparently faster and non-exponential ground-state recovery kinetics in the part of the absorption spectrum, overlapping with the fluorescence spectrum.