Electron transfer fluorescence quenching of napthalenediols by metal ions
Fluorescence quenching of four naphthalenediols (1,5-; 1,7-; 2,7-; 2,3-NDs) by transition metal ions (Cu2+, Co2+, Ni2+, Mn2+, Zn2+, Pb2+) has been investigated in 95% water-ethanol mixture. The dynamic quenching is appreciable with all metal ions except Pb2+. Cupric ion (Cu2+) is found to be an efficient quencher with all naphthalenediols and the sensitivity of 1,7-ND fluorescence is much higher than other naphthalenediols. The quenching rate constants (kq) have been analyzed for various possible mechanisms. A good correlation of log kq values with the reduction potentials of metal ions reveals the electron transfer quenching mechanism via a non-emissive exciplex with electron transfer from excited fluorophore to the metal ions. The anomalous behavior of 1,7-ND is explained by its point group symmetry and polarity.
Fluorescence quenching, Electron transfer quenching, Quenching, Transition metal ions, Naphthalenediols
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