Resumo

CARREON-CASTRO, M. del P et al. Optical properties and aggregation of 1-N-methylamino-4'-nitroazobenzene in various environments. Rev. mex. fis. [online]. 2008, vol.54, n.3, pp.229-235. ISSN 0035-001X.

Aggregation of 1-N-methylamino-4'-nitroazobenzene (RED-H) was studied by UV-vis spectroscopy in solution, using different methanol: water mixtures as solvents, at different concentrations. In 100 % methanol, methanol: water 80:20 and 60:40, RED-H exhibited an maximum absorption wavelength at λ = 477 nm and no aggregation was observed. By contrast, in mixtures of methanol: water 40:60 and 20:80 the appearance of an additional blue shifted band around λ =430 nm and a red shift of the absorption band to λ = 500 nm followed by a long tail confirmed the presence of both H-and J-aggregates in these solvents. Theoretical estimations of aggregate stability carried out at the LMP2/aug-cc-PVTZ(-f)//MP2/6-31G level of theory showed that the H-aggregate is the more stable one (-14.9 kcal/mol) stabilized mostly by electronic correlation while the J-aggregate is much less stable, being stabilized by electrostatic interactions (-3.4 kcal/mol). Theoretical estimation of the absorption spectra of RED-H, H- and J-aggregates carried out using the TD-B3LYP method reproduces the experimentally observed spectra. All electronic transitions show a strong charge-transfer component.

Palavras-chave : Aggregation; azo-dyes; DFT; LMP2; TD-DFT; optical properties.

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