Oxidative fluorescence quenching of Mg-phthalocyanine by quinones

•We have demonstrated the oxidative fluorescence quenching of MgPc with quinones.•Linear Stern-Volmer plot was obtained for the quenching of MgPc with quinones.•The nature of quenching is dynamic.•Singlet quenching rate constants are diffusion controlled in all solvents.•The quenching rate constants were decreased when the polarity of solvent is decreased.

The quenching of the excited singlet state of magnesium phthalocyanine (MgPc) by quinones was investigated in DMSO, acetonitrile and methanol. The quinones used were benzoquinone (BQ), duroquinone (DQ) and naphthaquinone (NQ). Fluorescence intensity/lifetime decreases with increasing concentration of the quinone following a linear Stern-Volmer behavior. Bimolecular quenching rate constants (kq) obtained from both the steady-state and time-resolved measurements for the singlet state quenching process were agreed well. Singlet quenching rate constants are diffusion controlled in all solvents. The quenching rate constants were decreased when the polarity of solvent is decreased. The thermodynamic parameter (ΔGet) estimated by using the Rehm-Weller equation were used to propose a suitable mechanism for electron transfer occurring between MgPc and quinones. The obtained ΔGet is more negative which clearly indicates that electron transfer type of mechanism is operative in these systems.