A computational study of substituted flavylium salts and their quinonoidal conjugate-bases: S0 -> S1 electronic transition, absolute pKa and reduction potential calculations by DFT and semiempirical methods

Autor(es)

Adilson A. Freitas ^[1] ; K. Shimizu ^[2] ; Luís G. Dias ^[3] ; Frank H. Quina ^[4]

Afiliação do(s) autor(es)

^[1] Universidade Técnica de Lisboa. Instituto Superior Técnico - Portugal

^[2] Universidade Técnica de Lisboa. Instituto Superior Técnico - Portugal

^[3] Universidade de São Paulo. Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto. Departamento de Química - Brasil

^[4] Universidade de São Paulo. Instituto de Química - Brasil

• Tipo de documento: Artigo Científico
• Fonte: Journal of the Brazilian Chemical Society; v. 18, n. 8, p. 1537-1546, 2007-00-00.

Resumo

The electronic transitions for flavylium cations and quinonoidal bases of 17 substituted flavylium salts have been studied at semiempirical and DFT (density functional theory) levels. Solvent effect on electronic spectra was included by Polarizable Continuum Model, PCM. We assigned longest-wavelength absorption maxima to HOMO -> LUMO transition. Both levels of theory gave good results for electronic transitions of flavylium cations whereas only TDDFT-PCM calculations could be used for electronic transitions of their quinonoidal bases. We also performed absolute pKa calculations of nine flavylium salts at DFT level. The pKa calculated values by our PCM parameterization gave excellent results with mean absolute deviation less than a half of one pKa unit. One-electron reduction potentials were carried out for 5 flavylium cations at DFT level. The theoretical results found were in good agreement with experimental values after adjustment for a systematic deviation. (AU)

• Processo FAPESP: 01/00973-1 - Reatividade quimica e fotoquimica de antocianinas em sistemas organizados.
• Beneficiário: Adilson Alves de Freitas
• Modalidade de apoio: Bolsas no Brasil - Doutorado
• Processo FAPESP: 01/05852-8 - Efeitos da solvatacao na hidratacao de compostos carbonilicos.
• Beneficiário: Karina Shimizu
• Modalidade de apoio: Bolsas no Brasil - Doutorado