DYNAMIC FLUORESCENCE STOKES SHIFT OF AN ACETYLENE-BRIDGED DONOR-ACCEPTOR COMPOUND IN ALCOHOLS AT LOW-TEMPERATURES

The time-dependent fluorescence Stokes shift p,p'-cyano thiomethyl diphenylacetylene in three different alcohols (1-propanol, 1-butanol, and 1-octanol) at room temperature was measured using time-correlated single photon counting and the spectral reconstruction method. These measurements were also performed with the probe in 1-propanol at low temperatures. The observed behavior is consistent with the dynamics of solvation of a polar excited state. As expected, the average solvation time increases with decreasing temperature and is correlated with solvent bulk viscosity down to 180 K. Apparent deviations observed at lower temperatures are attributed to the finite emission lifetime (≈1 ns) of the probe. A significant fast component (<100 ps) is observed in the dynamic Stokes shift even at temperatures close to the freezing point of 1-propanol. Different mechanisms that could result in such a fast component are discussed. © 1995 American Institute of Physics.