Femtosecond fluorescence spectroscopy and near-field spectroscopy of water-soluble tetra(4-sulfonatophenyl)porphyrin and its J-aggregate

Fluorescence dynamics of tetra(4-sulfonatophenyl)porphyrin (TPPS) in aqueous solution and mesoscopic structures of TPPS in thin films have been investigated by femtosecond fluorescence up-conversion spectroscopy and scanning probe microscopy (AFM/SNOM), respectively. We observed very short lifetime in B-state fluorescence of J-aggregate (140 ± 10 fs) which was shorter than that of monomer (200 ± 10 fs) and protonated monomer (530 ± 10 fs). In addition to the very short lifetime component in B state, we found very weak and short lifetime component in Q state of monomer TPPS. Fluorescence observed at the shorter wavelength edge of the monomer Q band has a comparable short lifetime of 240 ± 20 fs as well as B-state component which has been assigned to the fluorescence from Qy(0, 0) state. TPPS J-aggregate prepared by spin coating on the substrate shows quasi-2D nano-rod structures originated from the interaction between 1D J-aggregate. Large microcrystalline structures were observed in drop cast film. Near-field absorption and fluorescence images suggest the structural inhomogeneities of J-aggregate microcrystals.