FEMTOSECOND TRANSIENT ABSORPTION SATURATION IN POLY(ALKYL-THIOPHENE-VINYLENE)S

We report on ultrafast transient absorption measurements on solutions of poly(3-decyl-thiophene-2,5-diyl-vinylene), poly(3,4-dibutyl-thiophene-2,5-diyl-vinylene), and poly(3,3'-dibutyl-2,2'-dithiophene-5,5'-diyl-vinylene). In these polymers, a stiffening of the thiophenic backbone has been accomplished by inserting intrachain double bonds (vinyl groups). The transient absorption data seem to be consistent with the formation and decay of self-trapped excitons. The bleaching decays are independent of the size and location of the side groups, while they are sensitive to the backbone rigidity. A random-walk process on a finite polymer chain with recombination centers at the end is proposed to contribute to the relaxation mechanism of self-trapped excitons.