RATE OF PRIMARY PHOTOPRODUCT FORMATION FOR AQUEOUS CR(EN)33+ AND CR(NH3)5CL2+

High energy pulsed laser photolysis at 530 nm shows that in the case of aqueous Cr(en)33+ there is both a prompt and a delayed appearance of primary photoproduct, Cr(en)2(enH)(H2O)4+ (B). The latter grows in with the lifetime of emission from the first doublet thexi state, D10. Analysis of the variation of the ratio of delayed-to-prompt absorbance change indicates that the first quartet thexi state, Q10, is formed with 70% efficiency and then reacts to give B with a yield of 0.17. D10 is produced with 30% efficiency in a fast intersystem crossing, and then reacts to give B directly with a yield of close to unity. In the case of Cr(NH3)5Cl2+, the primary photoreaction gives cis-Cr(NH3)4(H2O)Cl2+ (AC). The appearance time is <5 ns, too short to allow identification of the reacting excited state. The pKa of AC is 6.2, and in neutral and alkaline solution the prompt absorbance change is followed by one of about 100 ns grow-in time, identified as the rate of proton transfer from AC to the buffer base. © 1979 American Chemical Society.