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A new homoleptic Cu(I) photosensitizer, Cu(dsbtmp)2(+) (dsbtmp = 2,9-di(sec-butyl)-3,4,7,8-tetramethyl-1,10-phenanthroline), designed to exhibit cooperative steric hindrance, unexpectedly produced strong photoluminescence (Φ = 1.9-6.3%) and long excited state lifetimes (τ = 1.2-2.8 μs) in a broad range of coordinating and noncoordinating solvents. The combination of the 2,9-sec-butyl substituents with the neighboring 3,8-methyl groups led to a Cu(I) complex with small degrees of ground and excited state distortion ultimately producing a molecule with robust metal-to-ligand charge transfer photophysics largely insulated from solvent interactions, reversible redox chemistry serving as a strong excited state reductant, along with impressive thermodynamic and photochemical stability in solution.
McCusker et al. (Mon,) studied this question.