Neutral platinum(II) diimine complexes undergo self-quenching in fluid solution, characterized by a linear increase in the emission decay rate with concentration. The corresponding quenching rates ( $10 9 -10 10 M À1 s À1 ) are nearly diffusion limited. The accumulated evidence suggests that an excited platinum complex, M*, reacts with a ground-state complex, M, to form an excimer, M 2 *, which rapidly relaxes to give two groundstate complexes. The reaction mechanism and the nature of the excimer are discussed in context of the electronic structures, spectroscopy, and quenching kinetics of these complexes. Steady-state cross-quenching experiments suggest that an excited platinum complex also can react rapidly ( $10 9 -10 10 M À1 s À1 ) with a different ground-state platinum diimine complex (Q), presumably to form an exciplex, MQ*. In contrast, aromatic molecules and platinum(II) complexes lacking a diimine ligand are relatively ineffective quenchers. These results suggest that both the diimine ligand and platinum center are important for quenching.

Pt(dbbpy)(bdt) and Pt(tmphen)(bdt) (dbbpy = 4,4'-di-t-butyl-2,2'-bipyridine; tmphen = 3,4,7,8tetramethyl-1,10-phenanthroline; bdt 2-= 1,2-benzenedithiolate) are reported. Pt(dbbpy)(bdt) reacts with one equivalent of methyl iodide to give the S-methylated product, [Pt(dbbpy)(CH 3 bdt)]I. The reaction follows second order kinetics with a rate constant of 1.3×10-2 M-1 s-1 at 311 K. The accumulated data are consistent with direct nucleophilic attack by the coordinated bdt 2ligand sulfur atom on the carbon atom of the methyl iodide. Variabletemperature experiments yield an Arrhenius activation energy of 51 ± 3 kJ/mol. Activated complex reaction theory yields an enthalpy and entropy of activation of 48 ± 2 kJ/mol and-125 ± 7 J/(mol K), respectively, consistent with an S N 2 reaction mechanism. The structure of the monosulfinate adduct, Pt(dbbpy)(bdtO 2), also is reported. The fluid-solution luminescence of Pt(tmphen)(bdt) is concentration dependent and characterized by a 1591  41 ns lifetime and 2.6 ± 0.2% quantum yield at infinite dilution. The observed chemical reactivity and self-quenching behavior have important implications for the design of photochemical devices based on the platinum(II) diimine dithiolate chromophore.

2002 coordination chemistry, review coordination chemistry, review Z 0150 45 -235 Self-quenching and Cross-quenching Reactions of Excited Platinum(II) Diimine Complexes. --(FLEEMAN, WENDI L.; CONNICK, WILLIAM B.; Comments Inorg. Chem. 23 (2002) 3, 205-230; Dep.