The fluorescence quenching of 5-phenyl-10,15,20-tris(p-sulfonatophenyl)porphine (TPPS3-) and 5,10,15,20-tetrakis(4-N-methylpyridyl)porphine (TMPyP4+) has been studied in water (pH 8.0) by using 9,10-anthraquinone-2,6-disulfonate (AQDS2-) and methyl viologen (MV2+) as quenchers. While electrostatic repulsion is expected, AQDS2- quenched the TPPS3- fluorescence more efficiently than MV2+. The steady-state and time-resolved fluorescence measurements indicated that static quenching took place in the TPPS3--AQDS2- system. Studies on the absorption spectra and the effects of ionic strength on the fluorescence quenching indicated the formation of the ground-state complex of TPPS3- and AQDS2-. The thermodynamic parameters (ΔH and ΔS) suggested that the ground-state complex was formed via van der Waals interaction.
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