DYNAMICS OF PHOTOEXCITATIONS IN A POLY[3-DODECYLTHIOPHENE] THIN-FILM STUDIED BY FEMTOSECOND VISIBLE-NEAR-INFRARED ABSORPTION-SPECTROSCOPY

Femtosecond transient absorption of a poly(3-dodecylthiophene) film is measured in a wide spectral range from visible to near-infrared. Our results show that the transient absorption consists of four decay comp onents. The two faster components are assigned to self-trapping and th e subsequent relaxation process of photogenerated excitons. The relaxa tion time constant of the self-trapped exciton is evaluated as 680 +/- 50 fs. The excited species corresponding to the third slow component is identified as a pair of intrachain, oppositely-charged polarons on the basis of its power-law decay and its spectral peak around 1.4 eV, A long-lived transient absorption due to interchain polarons is also o bserved. (C) 1998 Elsevier Science B.V. All rights reserved.