The concentration dependence of excimer fluorescence in polystyrene solutions

The fluorescence of high- and low-molecular-weight polystyrene in a variety of solvent conditions has been measured as a function of polymer concentration up to 650 g 1^-1. Measurements made using both a right-angle emission geometry and a front-face emission geometry confirm that self-absorption of fluorescence, particularly monomer fluorescence, leads to measurement of the ratio of excimer to monomer fluorescence intensities, I_E I_M, which overstates its true value at all but very low concentrations. When corrections are made for self-absorption effects, I_E I_M is essentially constant at low concentrations and increases only very slowly and smoothly at higher concentrations. Contrary to previous reports, no transition from a fractional power dependence to a linear dependence on concentration for I_E I_M has been observed at low polystyrene molecular weight.