Time-resolved microwave measurements of the polarizability of photoexcitons on conjugated polymer chains

Abstract

Changes as small as 1 ppm in the real and imaginary components of the complex permittivity resulting from flash photoexcitation of dilute solutions of (pi) -bond conjugated oligomers and polymers can be measured with nanosecond time resolution using the time-resolved microwave conductivity technique. The results provide information on the extent of delocalization of singlet and triplet state photoexcitations. Data are presented for oligomeric and polymeric derivatives of phenylene vinylene, paraphenylene and thiophene. For the polymers excess polarizability volumes, (Delta) V<SUB>p</SUB>, of the singlet exciton of 2000, 180 and 570 angstroms<SUP>3</SUP> are found, respectively. (Delta) V<SUB>p</SUB> for the triplet exciton of the polythiophene derivative is found to be only 25 angstroms<SUP>3</SUP>.