SYNTHESIS AND CHARACTERIZATION OF CYCLOMETALATED IRIDIUM(III) SOLVENTO COMPLEXES

Complexes of the type [Ir(L)(2)(S)(2)][OTf] have been prepared by reactions of [Ir(L)(2)Cl](2) with AgOTf in an appropriate solvent medium (L = 2-phenylpyridine (ppy) or 2-(p-tolyl)pyridine (ptpy); S = H2O or CH3CN; OTf = CF3SO3-). These solvento complexes have been characterized by H-1 and C-13 NMR spectroscopies, UV-visible absorption and emission spectroscopies, and cyclic voltammetry. Estimates of radiative lifetimes based upon weak integrated absorption bands in the 460-490-nm region are in agreement with emission lifetimes monitored in glasses at 77 K. Low-lying excited states responsible for these absorption and emission bands are assigned to an admixture of ligand-localized and metal-to-ligand charge-transfer character. Quenching of the emissions in ambient solutions is discussed in terms of ligand labilization due to either thermal population of metal-centered excited states or direct labilization in the MLCT excited state due to enhanced trans effects of the Ir-C bonds on the Ir-S bonding.