Ultrafast intersystem crossing in thiophene oligomers investigated by fs-pump-probe spectroscopy

摘要

Exciting the shortest members of thiophene oligomers, we observed ultrafast triplet formation on a time scale of 1.5-3 ps. From the time resolved transient spectra in terthiophene at different excitation wavelengths, we concluded the existence of an intermediate state within the S-1 manifold. This state is populated during the relaxation of the structure of the excited molecule to a planar conformation and can be the key for understanding the high triplet of about 0.95 in dioxane. In bithiophene, using two-photon excitation, we found excited state absorption, triplet-triplet absorption and radical cation absorption. The time constant for triplet formation was estimated to amount to 1.5 ps. [References: 6]