Photochemistry of copper(II) chlorocomplexes in acetonitrile: Trapping the ligand-to-metal charge transfer excited state relaxations pathways

Photochemistry of [Cu(MeCN)3Cl]+, [Cu(MeCN)Cl3]−, and [CuCl4]2− copper(II) chlorocomplexes in acetonitrile solution is studied by means of the combination of the steady-state photolysis and ultrafast transient absorption methods. The main relaxation pathways of the initially excited ligand-to-metal charge transfer states are internal conversion to the ground state, ionic dissociation without (photo)reduction of copper(II), and radical dissociation with (photo)reduction of copper(II). The copper(II)-to-copper(I) photoreduction quantum yields obtained from steady-state photolysis correlate with ultrafast spectroscopy data. The presence of oxygen does not affect the photoreduction quantum yields, which do not exceed 7% for the complexes studied and decrease in the series: [Cu(MeCN)3Cl]+ > [Cu(MeCN)Cl3]− > [CuCl4]2−.