Ultrafast Optical Response from a Novel Tri-Branched Copolymer

A novel tri-branched copolymer is synthesized to show strong two-photon absorption and intense two-photon absorption induced fluorescence emission under the excitation of the femtosecond laser pulses at wavelength of 800nm. The dynamics of the excited state was measured by the pump-probe technique. In a one-colour pump-probe experiment at 800nm, there was an ultrafast transient absorption, followed by other two relaxation processes. The two-photon absorption process could be one origin for this ultrafast photoabsorption signal, which was further proven by two-colour pump--probe experiments. The other two decaying processes in the transient absorption dynamics have lifetime of about 15ps and 129ps, which reflect the intraband vibrational relaxation and the decay of two-photon excited state, respectively.