Dispersive dynamics of photoexcitations in conjugated polymers measured byphotomodulation spectroscopy - art. no. 125206

We study the dynamics of the long-lived photoexcitations in p-phenylene-vin ylene based conjugated polymers containing acid-sensitive bipyridine subuni ts, and in poly(5,5'-vinylene-2,2 '-bipyridylene), by following the depende nce of the intensity of the photoinduced absorption bands on the laser modu lation frequency. The photoinduced absorption spectra contain two broad ban ds, whose relative intensities strongly depend on the protonation state of the polymers and whose modulation frequency dependence is distinctly differ ent. Whereas the higher-energy band follows the modulation frequency depend ence expected for either mono- or bimolecular recombination process, the lo wer-energy band shows a fractional power law frequency dependence at high m odulation frequencies, strongly indicating a "dispersive relaxation" proces s. The value of the fractional exponent is sample dependent and is a quanti tative measure for the distribution of the relaxing centers.