Triplet formation via ultrafast intersystem crossing in thiophene oligomers detected by fs-time resolved transient spectra

Summary form only given. Short thiophene oligomers especially bithiophene (2T) and terthiophene (3T) exhibit surprising high triplet quantum yields (up to 0.99 in 2T and 0.95 in 3T). These high triplet yields are responsible for their phototoxicity and their usage as photosensitizers. To explain the fast process of triplet formation, we investigated these molecules by means of fs-time-resolved spectroscopy in dependence on excitation wavelength. We found and examined ultrafast intersystem crossing proceeding in 1.5-3 ps. According to our proposed model, the planarization of the structure of the excited molecule plays the decisive role both in explaining the ultrafast kinetics as well as the high triplet quantum yields.