Doublet-doublet annihilation in chromium(III) polypyridine complexes

Under high-intensity pulsed laser excitation, the doublet states of Cr(4,7-Me2phen)33+ and Cr(phen)33+ decay with mixed first- and second-order kinetics. The dependence of the kinetics on laser intensity, presence of quenchers, and ionic strength demonstrates the occurrence of a doublet-doublet annihilation process in competition with the unimolecular doublet decay. The bimolecular rate constants for the annihilation process have been determined and found to be substantially lower than those for diffusion. Both energy-transfer and electron-transfer mechanisms for the annihilation process are discussed. © 1982 American Chemical Society.