Detection of transient CuICuICuII mixed-valence acetylide complexes from nanosecond transient absorption studies

Abstract

The photophysics of a series of luminescent trinuclear copper(I) acetylide complexes are described. These compounds are found to exhibit long-lived photoluminescence in fluid solutions at room temperature. The phosphorescent state of these trinuclear copper(I) acetylides are found to be efficiently quenched by pyridinium acceptors. Nanosecond transient absorption spectroscopy establishes the electron-transfer nature of these quenching reactions. Intense absorptions in the 790-830-nm near-infrared region have been attributed to the formation of transient mixed-valence trinuclear copper acetylide species. The transient decay of both the pyridinyl radical and the mixed-valence copper complexes has been shown to follow second-order kinetics. The back-electron-transfer rate constants have been estimated to be near diffusion-controlled, with k b = 2.3 × 10 10 dm 3 mol -1 s -1 for the reaction of 4-(methoxycarbonyl)-N-methylpyridinyl radical with [Cu 3(dppm) 3(μ 3-η 1-C≡CPh) 2] 2+ ([1] +), 1.7 × 10 10 dm 3 mol -1 s -1 with [Cu 3(dppm) 3(μ 3-η 1-C≡C tBu) 2] 2+ ([2] +), and 2.7 × 10 10 dm 3 mol -1 s -1 with [Cu 3(dppm) 3(μ 3-η 1-C≡CtBu)(μ 3-Cl)] 2+ ([3] +). © 1994 American Chemical Society.