Istituto dei materiali per l'elettronica ed il magnetismo     
Calzolari A., Varsano D., Ruini A., Catellani A., Tel-Vered R., Yildiz H., Ovits O., Willner I. Theoretical and experimental characterization of natural cyanin dyes. In: Joint ICTP-KFAS Workshop on Nanoscience for Solar Energy Conversion (Trieste (IT), 27 - 29 Ottobre 2008).
Flavonoids and anthocyanins in particular are very attracting compounds for their roles as natural dyes (from yellow to dark blue) in plants and flowers [1], as food pigments [2], as antioxidant agents in drug preparations [3] and recently as photoactive elements in dye-sensitized solar cells [4]. Anthocyanins give rise, in water, to many reactions including proton transfer, isomerization and tautomerization. In particular, as a function of the pH and/or the presence of metal cations, anthocyanins may undergo important structural changes, also causing dramatic loss of absorbivity. Despite the great amount of indirect experimental investigation, the direct mechanism of the anthocyanin hydration are still missing. Here, we present a combined theoretical and experimental study of the optical properties of a cyanin dye molecule (one of the most common anthocyanin) at room temperature. Absorption spectra in solution and on a semi-transparent Au electrode are compared with photocurrent measurements and ab initio DFT and TDDFT simulations, for different structural configurations that mimic the molecular rearrangement as a function of pH. Acknowledgement: This research is supported by the NanoSci-ERA project NanoLICHT, and the Regional Laboratory of Emilia Romagna "Nanofaber". Access to the CINECA supercomputing facilities was granted by CNR-INFM. [1] R. Brouillard and O. Dangles, in "The Flavonoids: Advanced research since 1986", J.B. Harborne (ed), Chapman and Hall London, pp. 565-587. [2] F. C. Stintzing, et al. J. Agric. Food Chem. 50, 6172 (2002) ; and J. He at al. J. Agric. Food Chem. 55, 4443 (2007). [3] J.I. Nakajima et al. J. Biol. Chem. 30, 21387 (2006). [4] N.J. Cherepy, et al. J. Phys. Chem. B 101, 9342 (1997).
Subject Flavonoids

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