A single- and double-flash flash photolysis study of the sequential biphotonic photoprocesses of Cu(i) phenanthrolines. Comparison of the helicate complex, [Cu2(1,3-bis(9-methyl-1,10-phenanthrolin-2-yl)propane)2]2+, and [Cu(2,9-dimethyl-1,10-phenanthroline)2]+ photoprocesses

Abstract

Photochemical processes induced when two photons are sequentially absorbed by the helicate complex [Cu₂(mphenpr)₂]²⁺, where mphenpr = 1,3-bis(9-methyl-1,10-phenanthrolin-2-yl)propane, and [Cu(dmp)₂]⁺ were investigated in CH₂Cl₂ containing solvents. A strong resemblance was observed between the fs–ns photophysics of [Cu₂(mphenpr)₂]²⁺ and Cu(I) phenanthroline complexes having a large steric hindrance. In the biphotonic regime, single-flash flash-photolyzed solutions were used for the determination of the product concentrations and quantum yields. The concentration of Cl⁻ produced by the photoinduced decomposition of CH₂Cl₂ increases linearly with flash intensity as expected for a monophotonic process. In contrast, the concentration of a decomposed Cu(I) complex exhibits the quadratic dependence on flash intensity of a biphotonic process. Results of a sequential double-flash flash photolysis experiment are consistent with the decomposition of CH₂Cl₂ ahead of the flattened excited state formation and with the absorption of the second photon by the flattened MLCT excited state.