Ultrafast excitation relaxation in titanylphthalocyanine thin film

Abstract Ultrafast excitation relaxation in the whole Q band of titanylphthalocyanine amorphous thin film fabricated by physical jet deposition was investigated by femtosecond time-resolved pump–probe technique. The measured relaxation dynamics was found to be strongly dependent on the wavelength of the laser beam and consists of three quite different processes: an ultrafast process with a lifetime of 0.5–5 ps, a fast and a long-lived processes with lifetimes of about 5–10 ps and longer than 100 ps, respectively. The initial ultrafast decay appearing to be excitation intensity dependent is suggested to represent a bimolecular exciton–exciton annihilation process with a t −1/2 time dependence of the excited-state population, assigned to a one-dimensional exciton diffusion. The exciton–exciton annihilation is observed in the pump intensity as low as 0.27 GW/cm 2 .