Photophysics and Electrochemistry of Biomimetic Pyranoflavyliums: What Can Bioinspiration from Red Wines Offer?

Natural dyes and pigments offer incomparable diversity of structures and functionalities, making them an excellent source of inspiration for the design and development of synthetic chromophores with a myriad of emerging properties. Formed during maturation of red wines, pyranoanthocyanins are electron-deficient cationic pyranoflavylium dyes with broad absorption in the visible spectral region and pronounced chemical and photostability. Herein, we survey the optical and electrochemical properties of synthetic pyranoflavylium dyes functionalized with different electron-donating and electron-withdrawing groups, which vary their reduction potentials over a range of about 400 mV.

Triplet Excited States and Singlet Oxygen Production by Analogs of Red Wine Pyranoanthocyanins.

During the maturation of red wines, the anthocyanins of grapes are transformed into pyranoanthocyanins, which possess a pyranoflavylium cation as their basic chromophore. Photophysical properties of the singlet and triplet excited states of a series of synthetic pyranoflavylium cations were determined at room temperature in acetonitrile solution acidified with 0.10 mol dm trifluoroacetic acid (TFA, to inhibit competitive excited state proton transfer) and at 77 K in a rigid TFA-acidified isopropanol glass.

Ground- and Excited-State Acidity of Analogs of Red Wine Pyranoanthocyanins.

Pyranoflavylium cations are synthetic analogs containing the same basic chromophore as the pyranoanthocyanins that form in red wine during maturation and are responsible for its final color. Determination of the ground- and excited-state acidities for a series of eight substituted hydroxy pyranoflavylium cations shows that they are weak acids in the ground state (pK ranging from 3.4 to 4.

Improved Synthesis of Analogues of Red Wine Pyranoanthocyanin Pigments.

An improved procedure is described for the preparation of pyranoflavylium cations from the reaction of 5,7-dihydroxy-4-methylflavylium cation with aromatic aldehydes. Modifications of the procedure of Chassaing et al. (.

Cucurbit[7]uril inclusion complexation as a supramolecular strategy for color stabilization of anthocyanin model compounds.

Host-guest complexation with cucurbit[7]uril of anthocyanin model compounds in which acid-base equilibria are blocked resulted in essentially complete stabilization of their color. The color protection is a thermodynamic effect and establishes a strategy to stabilize these colored compounds at pH values of interest for practical applications.