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-thiophe ne-2,5-diyl-vinylene), and 3,3'-dibutyl-2,2'-dithiophene-5,5'-diyl-vin ylene). 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 formati on and decay of self-trapped excitons. The bleaching decays are indepe ndent of the size and location of the side groups, while they are sens itive to the backbone rigidity. A random-walk process on a finite poly mer chain with recombination centers at the end is proposed to contrib ute to the relaxation mechanism of self-trapped excitons.