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Photoacidity of the 7‐Hydroxyflavylium Cation
Author(s) -
Aqdas Amna,
Siddique Farhan,
Nieman Reed,
Quina Frank H.,
Aquino Adelia J. A.
Publication year - 2019
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.13139
Subject(s) - chemistry , protonation , excited state , moiety , proton , photochemistry , conjugate acid , cationic polymerization , singlet state , photodissociation , molecule , chemical physics , proton affinity , computational chemistry , ion , atomic physics , stereochemistry , organic chemistry , physics , quantum mechanics
Theoretical descriptions of excited state proton transfer (ESPT) have had various degrees of success. This work presents a theoretical description of the photodissociation of the 7‐hydroxyflavylium cation ( 7‐HF ), the fundamental chromophoric moiety of anthocyanin natural plant pigments. ESPT of 7‐HF is promoted by a significant shift of charge away from the OH group in the first singlet excited state, leading smoothly to the excited conjugate base and a protonated water cluster. Several factors contribute to the consistency of the results of the present study: (1) the theoretical approach (TD‐DFT with the B3‐LYP functional and def2‐TZVP basis set utilizing Grimme's D3 dispersion correction); (2) the modeling of the solvent effect combining hydrogen bonding of the photoacid to a cluster of discrete water molecules in a water‐like continuum solvent (COSMO); (3) the large S 1 ‐S 2 energy gap of flavylium cations; and (4) the electrostatics of the ESPT in which a proton is transferred from a cationic photoacid to water without Coulombic interaction between the proton and the conjugate base.