DYNAMICS OF PHOTOINDUCED CHARGE-TRANSFER IN DIMETHYLAMINO-SUBSTITUTEDTRIPHENYLPHOSPHINES

Dimethylamino-substituted triphenylphosphines exhibit dual fluorescenc e in polar solvents. The long-wavelength band solvatochromism indicate s emission from a highly polar state with a 20 to 25 D dipole moment. Fluorescence decay measurements show that photoinduced intramolecular charge transfer occurs in a few picoseconds even in weakly polar solve nts and suggest that the charge transfer reaction is reversible leadin g to an equilibrium between the locally excited state and charge trans fer state populations during the excited state lifetime. A transient a bsorption band with a profile similar to that of the dimethylaniline c ation radical is observed in polar solvents by time-resolved picosecon d absorption spectroscopy. The reaction rate is found to decrease in v iscous solvents bringing support to a mechanism involving solute geome trical relaxation. On the other hand, the compounds are shown to form clusters and the role of clusters in the observed transient phenomena is discussed.