Efeitos do meio na estrutura conformacional e eletrônica de moléculas com grupos aceitador-doador
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2016-02-29
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Universidade Federal de Goiás
Resumo
The combined use of the Sequential QM/MM method with the ASEC mean field
approximation [1] and the Free Energy Gradient method [2] has been very successful in
describing the electronic structure of molecules in solution [3]. The advantage of this
combination is that it permits the usage of an atomic- level modeling of the whole
system, in contrast to continuum models, and, at the same time, it is less computationally
expensive than ab initio or QM/MM simulations, even allowing the employment of more
sophisticated electronic structure methods. In this context, the present work deals with
the study of conformational and electronic structure, in solvent medium, of two organic
compounds, DMACA and Phenol Blue, which have in common the characteristic of having
acceptor-donor groups. The study is conducted in the presence of nonpolar, polar protic
and polar aprotic solvents. It is adopted as basic methodology the ASEC-FEG, but also it
is made a study with a continuum method, namely PCM. The results show that the solvent
effect causes a significant geometric distortion of the molecules of interest while causing
an internal charge displacement from donor group to acceptor group. Both effects are
more pronounced in protic and aprotic solvents but mainly in protic solvents, in which
hydrogen bonds lead to a greater solute polarization. The absorption spectra of these
molecules, calculated by TD-DFT (CAM-B3LYP), directly reflect these changes. For all
solvents, the absolute values of electronic transitions and their respective solvatochromic
shifts are in good agreement with the experimental results.
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FRANCO, L. R. Efeitos do meio na estrutura conformacional e eletrônica de moléculas com grupos aceitador-doador. 2016. 110 f. Dissertação (Mestrado em Física) - Universidade Federal de Goiás, Goiânia, 2016.