EXCITED-STATE DYNAMICS OF RU(BPY)(3)(2+) ON POROUS VYCOR GLASS - INTERVENTION OF A LIGAND LOCALIZED TRIPLET-STATE

Absorption and emission spectra of Ru(bpy)(3)(2+) cation exchanged onto porous Vycor glass (PVG) closely resemble the corresponding aqueous solution spectra. However, complementary measurements of emission lifetime and quantum yield, Phi(em) reveal that, unlike fluid solution behavior where the ratio is temperature independent, the Phi(em)/tau ratio declines by 42% in the 5 to 90 degrees C range. The temperature dependence is due to the intersystem crossing efficiency, eta(isc), and a model consistent with both emission quantum yield and lifetime data indicates that the temperature dependence arises from the thermal population of a level that lies 1117 +/- 70 cm(-1) above the (1)MLCT state. This level is assigned to a ligand localized triplet state, (3)LL, and population of this state-leads to nonradiative decay competitive with intersystem crossing to the emissive manifold. As a result, the apparent intersystem crossing efficiency declines with increasing temperature. Although it is generally accepted that the intersystem crossing efficiency of Ru(II) diimines is independent of temperature, comparisons with currently available data show that eta(isc) can either increase or decrease with temperature when the complex possesses an asymmetric coordination environment. The asymmetry arises either from different ligands coordinated to Ru(II) or with Ru(bpy)(3)(2+) cation exchanged onto PVG, a differentiation of the initially equivalent ligands by the anionic surface of the glass. Under these conditions, intersystem crossing efficiency either increases or decreases with temperature depending on the relative energies of the (1)MLCT and (3)LL states.