Photo-physical behaviors of various active forms of curcumin in polar and low polar environments

- The properties of various forms of curcumin were studied by spectral and DFT methods.
- Curcumin indicates enol, diketone and deprotonated forms in various solvent media.
- Photo-physical properties of various forms depend on media induced interactions.
- During the excitation, the probability of charge transfer phenomena is increased.
- The results can give essential information on how this molecule can behave in biological systems.

The naturally occurring yellow-orange curcumin with wide applications in medical, biological and chemical phenomena have drawn considerable attention during the last years. The properties of molecular surrounding media can modify its various characteristics. In this paper, tautomerism of curcumin was investigated in the wide variety groups of solvents. In this case, photo-physical properties of curcumin in enol, diketone and deprotonated forms were investigated separately in polar and low polar solvents at room temperature by spectroscopic and theoretical techniques. Moreover, the most probable excitations of possible forms of curcumin in different solvent media were investigated by time-dependent density functional theory. Our results indicated that photo-physical behaviors of these forms depend strongly on the solvent polarity. In order to investigate the interactional behaviors of various forms of curcumin, we used the concept of linear salvation energy relationship proposed by Kamlet and Taft. Furthermore, according to the obtained results, the excited state dipole moments of various forms of curcumin with different resonance structures are higher than those in the ground state that increase the probability of charge transfer mechanism.

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