Investigation of aggregation of porphyrin derivative Fe(TPP)Cl at low temperature by time-resolved fluorescence spectrum

The time-resolved fluorescence spectrum I(, t) of the porphyrin derivative Fe(TPP)Cl in solution is measured. Experiments show that when the temperature is at least 5 K above the freezing point of the solvent, the sample fluorescence does not change with temperature. But when the temperature approaches the freezing point of the solvent, the fluorescence relaxation of the high concentration sample solution is faster than that of the above normal one. Furthermore, fluorescence spectra for various times after excitation have different shapes. Analysis shows that in this case the fluorescence is composed of two components with different relaxations and spectra. The two components are attributed to monomer and aggregates respectively.