Photophysics and Photochemistry of Tungsten Carbyne Complexes

Abstract

Transition metal complexes that luminesce at room temperature in fluid solution upon excitation with visible light have attracted much attention since such species have low-lying excited states which may allow the utilization of optical energy in the preparation of useful chemical products. Despite this interest only few such species have been discovered. In most cases luminescence is associated with a charge transfer transition involving metal dπ electrons and the π* orbital of ligated aromatic diimines. Here we describe some of the photophysical and photochemical properties of bis-donor ligand-substituted tungsten arylcarbyne complexes [(W=CAryl)X(CO)2L2] (X=halide, L=donor ligand) (Fischer 1977), a new class of luminescent organometallic species (Bocarsly 1985). The emissive excited state is associated with the lowest energy absorption band, which is assigned to a d-metal to π*(M=CAryl) transition. Quenching experiments indicate that a signi- ficant amount of triplet character is associated with the emissive excited state. Bimolecular oxidative and reductive charge transfer quenching is also observed, demonstrating the excited state to be strongly reducing and oxidizing. Photo- induced associative ligand substitutions occur in these molecules (Cameron 1986).