A BELL-SHAPE DEPENDENCE ON SOLVENT VISCOSITY OF THE FLUORESCENCE QUENCHING OF 9,10-DICYANOANTHRACENE BY OXYGEN IN SOLUTION

Effect of solvent viscosity on the fluorescence quenching of 9,10-dicy anoanthracene (DCNA) and 9,10-dimethylanthracene (DMEA) by oxygen has been investigated using time-resolved fluorescence decay measurements. When the viscosity, eta, was changed by applying hydrostatic pressure the fluorescence quenching of DMEA was found to follow k(q) is-propor tional-to 1/eta, whereas the fluorescence quenching of DCNA exhibits a bell-shape dependence on viscosity. The bell-shape dependence on the pressure-induced viscosity of the quenching rate constant is explained on the basis of a reaction intermediate between DCNA and ground stat e oxygen whose dissociative backward reaction exhibits stronger power dependence on solvent viscosity than the forward reaction.