Excited state relaxation in poly(spirobifluorene-co-benzothiadiazole) films.

Excited state relaxation of the poly(spirobifluorene-co-benzothiadiazole) has been investigated by means of the time resolved fluorescence and femtosecond transient absorption. The experimental results and their comparison with the similar data obtained for poly(fluorene-co-benzothiadiazole) show that the long-lived excited state with the reduced dipole moment of the transition to the ground state is formed on a subpicosecond time scale due to the exciton localization on a polymer backbone and spirobifuorene side group. Excited state stabilization reduces the transition dipole moment still further, causing fluorescence relaxation faster than the relaxation of the excited state. [ABSTRACT FROM AUTHOR]