Optical Properties of [Ru(phen)₂dppz]²⁺ as a Function of Nonaqueous Environment

The complex [Ru(phen)₂dppz]²⁺ is not photoluminescent in water but does emit in nonaqueous solvents (alcohols, acetonitrile) and in the presence of hydrated polymers such as DNA. Here we examine the steady-state and time-resolved photoluminescence spectra of [Ru(phen)₂dppz]²⁺ in a series of nonaqueous solvents. We find that solvent polarity, as defined by the E_T scale, is the single most important parameter in predicting luminescence lifetime and intensity in nonaqueous systems. These results are compared to the data for DNA, and the sequencedependent microenvironment of the complex bound to DNA also follows the trends observed herein. The addition of high concentrations of water to solutions of [Ru(phen)₂dppz]²⁺ dissolved in nonaqueous solvents leads to decreases in emission intensity that follow the Perrin sphere of quenching model. The nonradiative rate constants for luminescence decay increase as the solvent polarity increases, while the radiative rate constants are relatively unaffected by the local environment.