A fast relaxation of electronically-excited inclusion complexes of a styryl dye with cucurbit[7]uril

The relaxation of electronically-excited states of styryl dye (1) and its complexes with cucurbit[7]uril (CB[7]) in aqueous solution was studied by fluorescence steady-state and upconversion techniques. The decay of fluorescence, a 5-fold enhancement of which was observed upon addition of CB[7], was fitted to three exponential functions with time constants of 274, 43 and 1.8 ps in the presence of CB[7], and 100, 30, and 1.9 ps without it. In the framework of a simple model, based on the two-dimensional potential energy surface, the obtained results indicate that upon complexation the fluorescence rate constant of dye 1 increases by 3.8 times.