Fluorescence Quenching Studies of Curcumin by Hydrogen Peroxide in Acetonitrile Solution

Summary.

Steady state quenching studies of curcumin, 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione, fluorescence by hydrogen peroxide were conducted in acetonitrile solution. A quenching rate constant, k _q, of 1.05 × 10¹⁰  M ⁻¹ · s⁻¹ was obtained with a short fluorescence lifetime of 347 ps. The reaction rate constant, which is within the diffusion-limited regime, is activation-controlled. The rate constant of deactivation of the thermally excited curcumin was 1.2 orders of magnitude more nonradiative (2.67 × 10⁹ s⁻¹) than radiative (2.16 × 10⁸ s⁻¹). The reaction was exothermic with a ΔG° of −1.97 eV and solvent reorganization energy of 1.37 eV. These values indicate that the electron transfer reaction is solvent-mediated with electron transfer rate constant, k _ET, of 2.16 × 10¹⁰ s⁻¹.