Transient diffusion-mediated reversible association accompanied by generation and decay is studied using the method of convolution kinetics for the general scheme of intermolecular two-state excited-state processes. This scheme describes several important photochemical and photophysical processes including excimer formation, acid-base equilibria in the excited state, and association-dissociation of ions with their fluorescent indicators. The convolution-type integral kinetic equations are derived. The relation of the present approach to the extended Smoluchowski method is discussed.