MODULATION OF (d-$\pi^{*}\cdot(\pi-\pi^{*})$ CONFIGURATION INTERACTION IN IRIDIUM(III) COMPLEXES BY SOLVENT EFFECTS.

Abstract

In complexes of iridium(III) with several methyl- and phenyl-substituted 1,10-phenanthroline ligands, the lowest excited ligand-localized $(\pi-\pi^{})$ configuration is found to lie in close proximity to the lowest charge-transfer (d-$\pi^{}$) configuration. The resulting interaction of these zero-order configurations gives rise to a luminescent state which is described as an admixture of the two configurations. The radiative properties of this state are determined by the contribution from $d\pi^{}$ configuration which carries a far greater oscillator strength than the $\pi^{}$ configuratio. The luminescent state is found to display a lifetime which depends upon the solvent medium at $77^{\circ} K$. The variation in the lifetime can be correlated with the movement of the charge-transfer configuration whose contribution to the luminescent state is a function of the energy gap between the zero-order configurations. From a study of the dependence of the luminescence lifetimes on the energy gap displayed in various solvents, the matrix element responsible for coupling the $\pi^{}$ and d-$\pi^{}$ configurations is estimated to be $230 cm^{-1}$.