Platinum diimine complexes: towards a molecular photochemical device

Complexes having the general formula PtX2(diimine) where X-2 = dithiolate, bis(acetylide) and diimine = bipyridine, phenanthroline and derivatives have been investigated for potential use as chromophores in the conversion of light-to-chemical energy. These complexes, like the analogous X = CN systems, are luminescent in fluid solution. Previous studies of the dithiolate derivatives reveal that they possess a charge transfer excited state involving a mixed metal-dithiolate donor orbital and a pi*(diimine) acceptor function with excited state properties including emission energies, lifetimes and redox potentials that are tunable by ligand variation. The bis(acetylide) complexes are brightly luminescent in fluid solution, and their excited state is shown to be MLCT in character, consistent with an earlier proposal, Both sets of diimine complexes show evidence of self-quenching, and for Pt(phen)(CCPh)(2), weak excimer emission is observed. The mechanism of quenching has been probed through cross-quenching experiments and is thought to involve Pt...Pt interactions. Efforts are now focussing on the use of the PtX2(diimine) chromophores in dyads and triads with the goal of constructing a molecular photochemical device for light-to-chemical energy conversion. Connection of the Pt diimine chromophores to both a donor or reductive quencher and an acceptor is envisioned through new ligand bridges currently being synthesized using Pd-catalyzed coupling reactions and carbonyl condensations. (C) 2000 Elsevier Science S.A. All rights reserved.