Size dependent ultrafast dynamics of oligothiophenes with 1–4 monomer units

We studied size-dependent dynamics of oligothiophene with 1–4 monomer units at varied pump energy by subpicosecond pumpprobe technique. Ultrafast triplet formation was observed after two-photon absorption in thiophene (1T) and bithiophene (2T). Triplet formation in 3T and 4T can be fitted by biexponential functions. The fast component amonts to 2 ps for 3T. The slow one is dependent on photon energy of excitation.