| Abstract
| - Picosecond time-resolved resonance Raman (picosecond-TR3) spectroscopy has been used to conduct anextensive photophysical characterization of the “light-switch” complex [Ru(phen)2dppz]2+ as a function ofenvironment, in which studies have been carried out in aqueous and nonaqueous media and in DNA. Theresults are considered in relation to a previous report describing “environment-sensitive” lowest triplet MLCTstates. Vibrational marker features and enhancement patterns were used to determine the rapid progression(<20 ps) between two triplet MLCT states in aqueous environment, followed by subnanosecond, nonradiativedeactivation to the ground state. In nonaqueous environment, the long-lived, emissive triplet MLCT state isspectrally identified as the short-lived first triplet MLCT state observed in water, in agreement with the earlierproposed mechanism. The present data are shown to correlate well with previous nanosecond RR findingsfor the complex in each environment. Interestingly, a “precursor state” has been identified upon excitation inboth nonaqueous solvent and in DNA, which precedes the triplet MLCT state, and the lifetime of whichappears to be environment dependent. Observation of this state is discussed in relation to other recentfemtosecond spectroscopic studies on this complex.
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