Photoinduced electron transfer (PET) in ethaline-like solvents

Deep eutectic solvents (DESs) are 21st century solvents composed entirely of hydrogen bond donors and acceptors, which form a eutectic solvent having a significantly lower melting point than its individual components. Due to their tunable nature, DESs are widely employed for applications in electrochemistry, nanotechnology, catalysis and synthesis but their intrinsic electron transfer behaviour is largely unexplored. In order to characterize electron transfer in DESs, steady state reductive emission quenching measurements were performed using tris(2,2'-bipyridine)ruthenium(II), [Ru(bpy)₃]²⁺, with a series of quenchers in several different volumetric compositions of ethaline (choline chloride:ethylene glycol) and water. Using Stern-Volmer analysis, rate constant (k_q) values for excited state quenching were calculated and compared with diffusion limited rate constant (k_D) data. Finally, the electron transfer data were further analyzed by fitting to Rehm-Weller and Marcus theory models in order to provide a theoretical framework for understanding and predicting electron transfer kinetics.