Time‐Resolved Fluorescence Spectroscopy of Porphyrin J‐Aggregates Using Optical Kerr Gate Methods

Abstract We observed for the first time ultra‐fast relaxation process due to internal conversion from S 2 ‐exciton to S 1 ‐exciton in porphyrin J‐aggregates using the optical Kerr gate method. The S 2 fluorescence shows sharp spectra with almost zero Stokes shift. The decay time is less than the instrumental function and cannot be time‐resolved by the Kerr gate method. The relaxation time of the S 2 ‐exciton was also measured by pump‐probe spectroscopy with about 10 fs resolution, and the decay time, 130 ± 10 fs, was consistently obtained with that of the S 2 fluorescence.