Phase jump in wavelength dependence of coherent vibration in porphyrin J-aggregates by sub-5-fs spectroscopy

摘要

Molecular J-aggregates have attracted much attention because of the ultrafast and large optical nonlinearity caused by the excitonic resonance. The one-dimensional porphyrin J-aggregates show sharp absorption peaks at 2.53 eV (S{sub}2-state: B-band) and 1.75 eV (S{sub}1-state: Q-band) composing a three-level Frenkel exciton system, which is depicted in Fig. 1. A modulation of the induced absorbance change by coherent oscillation of 244 cm{sup}(-1)- ruffling mode was observed for the first time by sub-5-fs pump-probe experiment of porphyrin J-aggregates. In particular, the phase of the oscillation showed a pi-phase difference between the bleaching and the induced absorption of the multi-exciton states (MES). A one-dimensionally oriented film of porphyrin J-aggregates was prepared by the vertical spin-coating. The sample was pumped and probed with the sub-5-fs pulses at room temperature. The polarization of the pump and probe, and the orientation of the aggregates were parallel to each other.