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Published on: July 19, 2016
Temperature and solvent-dependent photoluminescence quenching in [Ru(bpy)2(bpy-cc-AQ)]2
1Stanford PULSE Institute, SLAC National Accelerator Laboratory, Stanford University, 2575 Sand Hill Road, Menlo Park, CA 94025, USA. cblarsen@stanford.edu.
Abstract:
I have herein investigated the solvent-dependent photoluminescence quenching mechanism of [Ru(bpy)2(bpy-cc-AQ)]2+ using variable temperature emission spectroscopies. The photophysics of this complex are dominated by an excited-state thermal equilibrium between a photoluminescent 3MLCT state and a charge-separated state that lies higher in energy relative to the 3MLCT state in low polarity solvents and approximately isoenergetic in high polarity solvents. Furthermore, an unusual photoluminescence temperature-dependence in high polarity solvents is shown to arise from competition between enthalpic factors favouring the charge-separated state and entropic factors favouring the photoluminescent 3MLCT state, analogous to the molecular light-switch effect of [Ru(bpy)2(dppz)]2+. The solvent-dependent photoluminescence quenching of [Ru(bpy)2(bpy-cc-AQ)]2+ is attributed to two key solvent-dependent factors: (1) the excited-state equilibrium position and (2) the rate of charge-recombination from the charge-separated state.
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