The title assembly diplays an emissive rhenium-to-pyridine charge-transfer state that is partially quenched by electron transfer to an attached acceptor (nitrobenzene). Quenching is preceded by intramolecular folding (J. Am. Chem. Soc. 1993, 115, 2048). Variable-temperature quenching measurements can be used to determine the characteristic temperature, Ttr, above which unfolded photoexcited state conformations become favored over folded conformations. Similar information for the ground state can be obtained from variable-temperature NMR measurements. Studies in eight solvents show that excited state folding is (1) enthalpically favored but entropically disfavored (all solvents), (2) correlated (via Ttr) with the inverse dielectric strength of the solvent, and (3) enhanced in comparison to folding in the electronic ground state (studies in one solvent). The combined evidence points to a folding reaction that is driven by optimization of localized Coulombic interactions. Optimization of solvent cohesive interactions, however, may possibly also play a role in the folding reaction.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry