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Triplet Excited States and Singlet Oxygen Production by Analogs of Red Wine Pyranoanthocyanins
Author(s) -
Silva Gustavo Thalmer M.,
Thomas Suma S.,
Silva Cassio Pacheco,
Schlothauer Jan C.,
Baptista Mauricio S.,
Freitas Adilson A.,
Bohne Cornelia,
Quina Frank H.
Publication year - 2018
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/php.12973
Subject(s) - photochemistry , chemistry , flash photolysis , excited state , triplet state , singlet fission , singlet oxygen , acetonitrile , chromophore , singlet state , trifluoroacetic acid , phosphorescence , oxygen , redox , molecule , inorganic chemistry , organic chemistry , fluorescence , kinetics , atomic physics , physics , quantum mechanics , reaction rate constant
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 −3 trifluoroacetic acid (TFA, to inhibit competitive excited state proton transfer) and at 77 K in a rigid TFA‐acidified isopropanol glass. In solution, the triplet states of these pyranoflavylium cations are efficiently quenched by molecular oxygen, resulting in sensitized formation of singlet oxygen, as confirmed by direct detection of the triplet‐state decay by laser flash photolysis and of singlet oxygen monomol emission in the near infrared. The strong visible light absorption, the relatively small singlet‐triplet energy differences, the excited state redox potentials and the reasonably long lifetimes of pyranoflavylium triplet states in the absence of molecular oxygen suggest that they might be useful as triplet sensitizers and/or as cationic redox initiators in polar aprotic solvents like acetonitrile.