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Issue 40, 2016
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Excited-state dynamics of the medicinal pigment curcumin in a hydrogel

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Abstract

Curcumin is a yellow polyphenol with multiple medicinal effects. These effects, however, are limited due to its poor aqueous stability and solubility. A hydrogel of 3% octadecyl randomly substituted polyacrylate (PAAC18) has been shown to provide high aqueous stability for curcumin under physiological conditions, offering a route for photodynamic therapy. In this study, the excited-state photophysics of curcumin in the PAAC18 hydrogel is investigated using a combination of femtosecond transient absorption and fluorescence upconversion spectroscopy. The transient absorption results reveal a multiexponential decay in the excited-state kinetics with fast (1 ps & 15 ps) and slow (110 ps & ≈5 ns) components. The fast decay component exhibits a deuterium isotope effect with D2O in the hydrogel, indicating that the 15 ps decay component is attributable to excited-state intramolecular hydrogen atom transfer of curcumin in the PAAC18 hydrogel. In addition, solvent reorganisation of excited-state curcumin is investigated using multiwavelength femtosecond fluorescence upconversion spectroscopy. The results show that the dominant solvation response (τ = 0.08 ps) is a fast inertial motion owing to the presence of bulk-like water in the vicinity of the hydrophobic octadecyl substituents of the PAAC18 hydrogel. The results also show an additional response with longer time constants of 1 and 6 ps, which is attributable to translational diffusion of confined water molecules in the three-dimensional, cross-linking network of the octadecyl substituents of PAAC18. Overall, we show that excited-state intramolecular hydrogen atom transfer and solvent reorganisation are major photophysical events for curcumin in the PAAC18 hydrogel.

Graphical abstract: Excited-state dynamics of the medicinal pigment curcumin in a hydrogel

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Supplementary files

Article information


Submitted
15 Aug 2016
Accepted
22 Sep 2016
First published
23 Sep 2016

Phys. Chem. Chem. Phys., 2016,18, 28125-28133
Article type
Paper

Excited-state dynamics of the medicinal pigment curcumin in a hydrogel

T. Harada, S. F. Lincoln and T. W. Kee, Phys. Chem. Chem. Phys., 2016, 18, 28125
DOI: 10.1039/C6CP05648B

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