Study of the fluorescence-quenching of Mg-TNP by anionic anthraquinones

Abstract

The fluorescence quenching of magnesium 5,10,15,20-tetra-p-naphtyl-porphyrin (Mg-TNP) has been studied in benzene using 9,10-anthraquinone-2-sulfonic acid sodium salt (An 1), 9,10 -anthraquinone-2,6-disulfonic acid sodium salt monohydrate (An 2), 9,10-anthraquinone-1,5-disulfonic disodium salt monohydrate (An 3) as quenchers. The fluorescence quenching rate constants are deduced from the Stern-Volmer curves and it is postulated that the quenching occurs via the formation of a charge transfer complex formation. For all these cases, R(o)values are in the 1-10 Angstrom range, which correspond to one singlet quenching processes by diffusion controlled energy transfer. Electron-exchange and/or electron transfer processes are expected to proceed also at these distances. The quenching mechanism is concerted one between static quenching with energy transfer (due to long-range dipole-dipole interaction between excited anthraquinone molecules (donor) and the ground state acceptor molecule Mg-TNP) and electron transfer which should occur from singlet excited state of Mg-TNP to donor anthraquinone molecule, leading to formation of stable radical anion and cations.