INTRAMOLECULAR EXCIMER FORMATION IN MODEL COMPOUNDS FOR POLYESTERS - DIESTERS FROM 2-NAPHTHOL AND ALIPHATIC DICARBOXYLIC-ACIDS

The propensity for the formation of bends in the flexible spacer in polyesters containing naphthyl units has been examined by the study of the fluorescence of a series of diesters. Steady state fluorescence spectra have been measured for the diesters Naph-OOC-(CH2)m-COO-Naph, m = 2-6, 'Naph' = 2-naphthyl, in dilute solution in solvents of differing viscosity, eta. The dependence of the degree of intramolecular excimer formation on m, under circumstances where the dynamics of rotational isomerism in the flexible spacer is suppressed, is evaluated by extrapolation of the measurements to infinite-eta. The extrapolated results exhibit an odd-even effect, with the more intense excimer emission being observed when m is odd. The odd-even effect is rationalized by a rotational isomeric state analysis of the diesters.