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Evidence for excited state intramolecular charge transfer in benzazole-based pseudo-stilbenes.
Santos, Fabiano da Silveira; Descalzo, Rodrigo Roceti; Gonçalves, Paulo Fernando Bruno; Benvenutti, Edilson Valmir; Rodembusch, Fabiano Severo.
Afiliación
  • Santos Fda S; Laboratório de Novos Materiais Orgânicos, Universidade Federal do Rio Grande do Sul - Instituto de Química, Avenida Bento Gonçalves, 9500, CP 15003, CEP 91501-970 Porto Alegre-RS, Brazil.
Phys Chem Chem Phys ; 14(31): 10994-1001, 2012 Aug 21.
Article en En | MEDLINE | ID: mdl-22782066
Two azo compounds were obtained through the diazotization reaction of aminobenzazole derivatives and N,N-dimethylaniline using clay montmorillonite KSF as catalyst. The synthesized dyes were characterized using elemental analysis, Fourier transform infrared spectroscopy, and (13)C and (1)H NMR spectroscopy in solution. Their photophysical behavior was studied using UV-vis and steady-state fluorescence in solution. These dyes present intense absorption in the blue region. The spectral features of the azo compounds can be related to the pseudo-stilbene type as well as the E isomer of the dyes. Excitation at the absorption maxima does not produce emissive species in the excited state. However, excitation around 350 nm allowed dual emission of fluorescence, from both a locally excited (LE, short wavelength) and an intramolecular charge transfer (ICT, long wavelength) state, which was corroborated by a linear relation of the fluorescence maximum (ν(max)) versus the solvent polarity function (Δf) from the Lippert-Mataga correlation. Evidence of TICT in these dyes was discussed from the viscosity dependence of the fluorescence intensity in the ICT emission band. Theoretical calculations were also performed in order to study the geometry and charge distribution of the dyes in their ground and excited electronic states. Using DFT methods at the theoretical levels BLYP/Aug-cc-pVDZ, for geometry optimizations and frequency calculations, and B3LYP/6-311+G(2d), for single-point energy evaluations, the calculations revealed that the least energetic and most intense photon absorption leads to a very polar excited state that relaxes non-radioactively, which can be associated with photochemical isomerization.

Texto completo: 1 Colección: 01-internacional Base de datos: MEDLINE Idioma: En Revista: Phys Chem Chem Phys Asunto de la revista: BIOFISICA / QUIMICA Año: 2012 Tipo del documento: Article País de afiliación: Brasil Pais de publicación: Reino Unido

Texto completo: 1 Colección: 01-internacional Base de datos: MEDLINE Idioma: En Revista: Phys Chem Chem Phys Asunto de la revista: BIOFISICA / QUIMICA Año: 2012 Tipo del documento: Article País de afiliación: Brasil Pais de publicación: Reino Unido