Ultrafast exciton and excited-exciton dynamics in J-aggregates of three-level porphyrin molecules

摘要

We observed the ultrafast response of exciton (S__1-excition) and excited-exciton (S_2-excition) in one-dimensional J-aggregates of three-level porphyrin molecules by femtosecond pump-probe spectroscopy. The decay profiles of the nonlinear response can be fitted to a sum of instantaneous response and two exponential decay components with time constants of 1.3 +- 0.1 and 40 +- 1 ps. The former and latter were found to correspond to the lifetimes of S_2- and S_1-excitons, respectively. The origins of the nonlinearity were attributed to the following three contributions: (1) coherent effects between the pump and probe via one-photon virtual S_1-excition, (2) induced absorption of real S_2-excitons generated by two photons, and (3) induced absorption of real S_1-exciton.