We present a study of the photoexcitation mechanism of poly-3- alkylthienylene and poly-3-alkylthienylenevinylene polymer solutions. We study the photoinduced absorption under steady-state and far from steady-state conditions. By calculating the analytical dependence of the photoinduced signal on the pump intensity and on the chop frequency we distinguish a bimolecular recombination mechanism for both single chain and aggregated chain solutions. The results are discussed assuming that a weak reversible charge transfer between the photoexcited polymer and the solvent takes place. © 1993 The American Physical Society.