Fluorescence and time-resolved delayed luminescence of porphyrins in organic solvents and polymer matrices

Porphyrin dyes fulfill an essential function in photosynthesis and are impo rtant in photodynamic therapy and in a range of electronic devices. Their s pectroscopic characteristics may play a crucial role in these processes. Th e spectral properties of two porphyrin dyes: tetraphenylporphyrin and tetra phenysulfporphyrin in organic solvents (acetone, chloroform, methyl alcohol , and dimethylsulfoxide) and in polyvinyl alcohol and poly(methylmethacryla te) films have been investigated. Absorption, fluorescence, and microsecond time-resolved delayed luminescence spectra have been measured at room temp erature. The existence of different aggregated dye forms in the ground and excited states has been demonstrated. The manifold of dye species depends o n the solvent/polymer. In the case of the polymers, it also depends on the solvent used to coat the polymer film. Delayed luminescence spectra and dec ay times of the two porphyrins in the different solutions and in polymeric matrices suggest that different mechanisms of deexcitation of the singlet e xcited states may be responsible for their generation in these and other po rphyrin dyes.