Inter- and Intramolecular Interactions of Polymer as Studied by Fluorescence Spectroscopy. XI. Solvent and Concentration Effects on the Exciplex Emission by Poly[oxy-2-(1-pyrenylmethyl)propyleneoxy-(4-N,N-dimethylaminobenzyl)malonyl

Abstract

Solvent and concentration effects on the exciplex formation by poly[oxy-2-(1-pyrenylmethyl)propyleneoxy-(4-N,N-dimethylaminobenzyl)malonyl] (I) (DP<18) are discussed for three solvents. The dimer model compound, 1-acetoxy-2-(1-pyrenylmethyl)propyleneoxy-(4-N,N-dimethylaminobenzyl) malonyloxyethane (II) was prepared from the corresponding halfester of the 1,3-propanediol with the corresponding diethyl malonate. From the results of absorption, emission and excitation spectra, the solvent and molecular weight effects on inter- and intramolecular interactions of the I system were compared with those of II. The ratio of exciplex emission intensity (Fe) to monomer emission intensity by pyrenyl groups (Fm) increased with concentration, suggesting an interpolymer association of I in a concentration region below 10−5 M whereas exciplex by II was concentration independent. When the initial slopes of Fe/Fm vs. concentration were plotted against the degree of polymerization (DP), there was found an optimum DP for intermodular interactions of the polymer. The facts that the interpolymer exciplex formation was most efficient in the intermediate DP region, and that the optimum DP value for interpolymer association was higher in a good solvent (1,2-dichloroethane) than in a poor solvent (mesitylene), may be considered as important findings. The mixing of emission by an excited ground state complex with true exciplex emission was suggested by the dependence of the shape of the apparent exciplex emission on the excitation wavelength.