COIL SIZE AND LONG-RANGE EXCIMERS .1. SOLVENT-SOLVENT MIXTURES

Fluorescence spectra of polyacenaphthylene (PAN) were determined in di lute solution at a constant temperature, 25.0-degrees-C. Solvents were prepared by mixing two good solvents in different proportions. Solven t viscosity (eta) and polymer intrinsic viscosity ([eta]) were also me asured at 25.0-degrees-C for each solvent composition. Solvent mixture s were chosen to show a monotonous change of only solvent fluidity (et a-1) (benzene-dioxane) and both eta-1 and [eta]-1 simultaneously (tetr ahydrofuran-dioxane, chloroform-tetrahydrofuran, and cyclohexane-dieth yl ether). A single solvent, toluene, was also used. The dependence of the excimer to monomer fluorescence ratio on solvent viscosity and se gmental density (directly proportional to [eta]-1) has been discussed in terms of a kinetic scheme which takes into account energy migration , ground state preformed dimers, and unquenched monomeric units. It pr edicts that the excimer to monomer fluorescence ratio depends on the p roduct eta-1[eta]-1.