Solvent dependent photophysical properties of dimethoxy curcumin

Dimethoxy curcumin (DMC) is a methylated derivative of curcumin. In order to know the effect of ring substitution on photophysical properties of curcumin, steady state absorption and fluorescence spectra of DMC were recorded in organic solvents with different polarity and compared with those of curcumin. The absorption and fluorescence spectra of DMC, like curcumin, are strongly dependent on solvent polarity and the maxima of DMC showed red shift with increase in solvent polarity function (Delta f), but the above effect is prominently observed in case of fluorescence maxima. From the dependence of Stokes' shift on solvent polarity function the difference between the excited state and ground state dipole moment was estimated as 4.9 D. Fluorescence quantum yield (phi(f)) and fluorescence lifetime (tau(f)) of DMC were also measured in different solvents at room temperature. The results indicated that with increasing solvent polarity, phi(f) increased linearly, which has been accounted for the decrease in non-radiative rate by intersystem crossing (ISC) processes. (C) 2012 Elsevier B.V. All rights reserved.