COMPARATIVE ELECTRON-TRANSFER QUENCHING RATES OF 9,10-DICYANOANTHRACENE BY VARIOUS DONORS IN SOLVENTS OF DIFFERENT POLARITIES

Multiple Rehm-Weller plots of the rate constants of quenching of 9,10-dicyanoanthracene fluorescence by electron transfer with a variety of donors of different adiabatic ionization potentials have been observed in polar solvents (1-fluoropentane and acetonitrile). The donors fall into two classes which can be described as 'n' (localised positive charge in the cation) and 'pi' (delocalised charge), the former being the more efficient quenchers. Possible reasons for this difference are discussed: electrostatic and solvation energies, internal reorganisation energy. Current evidence favours the former explanation.