Chelation and fluorescence properties of tetraphenylporphyrin and 5,10,15,20-tetra(4-hydroxyphenyl)porphyrin in acetonitrile

The kinetics of complex formation between zinc and 5,10,15,20-tetraphenylporphyrin and 5,10,15,20-tetra(4-hydroxyphenyl)porphyrin in acetonitrile is studied in the temperature range from 298 to 318 K. The fluorescent properties of these compounds are examined, the emission in the red region of the spectrum is measured, and the fluorescence quantum yields are determined. It is found that although the electronic absorption spectra of the studied compounds are almost identical, hydroxyl substituents are observed to have a considerable effect on the chelating ability of ligands. The rate constant of the formation of ZnT(4-OH-Ph)P is thus approximately three times higher than that of ZnTPhP, with the energy consumption being lower (about 20 kJ mol–1). The calculated fluorescence quantum yields of H2TPhP, H2T(4-OH-Ph) P, ZnTPhP, and ZnT(4-OH-Ph)P in acetonitrile are half those in toluene, while the ratio between the quantum yields of ligands and their metal complexes is a constant equal to approximately 3 and does not depend on which solvent is used.