We demonstrate that reversible reactions occurring in the excited electroni
c state undergo a 'kinetic transition' as a function of the difference in e
xcited-state decay rates. This conclusion follows from a remarkably accurat
e approximate solution obtained for the kinetics of diffusion-influenced re
versible geminate dissociation reactions in solution, which becomes exact a
t long times. (C) 1999 Elsevier Science B.V. All rights reserved.