Spectroscopic and photophysical studies of the hydroquinone family of photochromic Schiff bases analyzed over a 17-orders-of-magnitude time scale.

The hydroquinone family of photochromic Schiff bases has been studied by means of stationary and time-resolved spectroscopic absorption and emission techniques in the UV-Vis spectral range in the temporal range from 100 fs to 1 h. The studies have revealed that besides the ultrafast excited state intramolecular proton transfer reaction there is also another deactivation channel from the initially excited state. For the symmetric molecule with two intramolecular hydrogen bonds, the efficiency of the proton transfer reaction has been found to be at least ten times reduced when compared to that of the asymmetric molecule with one intramolecular hydrogen bond. The long-lived transient species absorbing in the UV range and coexisting with the photochrome have been observed in differently interacting solvents. Evidence for different conformers of almost all of the tautomers involved in the photochromic cycle has been also found.