Self-trapped exciton dynamics in highly ordered and disordered films of polythiophene derivative

We measured the time-resolved photoluminescence of highly ordered and disordered films of a polythiophene derivative, poly(3-[2-((S)-2-methylbutoxy)ethyl]thiophene). The formation of self-trapped excitons (STE's) within 10 ps after photoexcitation and the subsequent migration of the STE's are common behavior in both films. The spectral narrowing of the phonon sidebands within 10 ps after photoexcitation is associated with the formation process of STE's and the spectral changes on a few hundred ps time scale are explained by the STE migration and the dependence of the electron-phonon coupling on the effective conjugation length.