In this work, Raman spectroscopy and density functional theory (DFT) calculations have been used in order to understand the nature of the interaction between the carotenoid bixin and organic solvents with dielectric constant varying from ca. 2 (toluene) to ca. 47 (dimethyl sulfoxide). Raman shifts registered for the main carotenoid marker band, the C=C stretching mode (1525-1533 cm-1), were used as a probe to monitor spectral changes due to chemical interaction between bixin in the solid state with the analogous solvated species. Raman spectra of bixin in solution showed significant bathochromic shifts in the wavenumber position of ν(C=C) when compared with the solid state. Among the solutions, subtle differences were observed and the polarizability rather than dielectric constant of the solvents seems to be a more appropriate parameter to explain the differences in Raman shifts which could be correlated with the solvation degree of bixin. Correlation between DFT analysis and molecular dynamics simulations obtained for cis-bixin in DMSO and CHCl3 demonstrated that the interaction of the solute with the respective solvents occurs in specific portions of the molecule, however, this result was not confirmed by the experimental data since bixin is solvated by larger numbers of solvent molecules.

This work shows a practical application of the group theory to a relatively simple molecular system, as well its impact in the results obtained through vibrational spectroscopic techniques. Squaraines substituted by dicyanemethylene groups have been extensively studied, and after minor approaches in the sense to facilitate the point group determination, they were classified to the C2v (Cis) and D2h (Trans) groups. The Trans squaraine presents lower irreducible representations when compared to the Cis derivative; alterations in the arrangements of such systems promotes very interesting conjugation effects, since different reactivity from spectroscopic particularities. Especially to the Trans squaraine, there was a clear convergence between the data suggest by the calculations and those observed in their vibrational spectra, mainly that related to the inversion operation; strong bands visualized in a vibrational technique are not identified in other, mainly in region between 1800-1000 cm-1. The approach of local symmetry must to be adjust to better evaluation of the spectroscopic behavior of the Cis derivative, in this case, the theory suggests low symmetry, but in the spectra can be seen clearly a bigger symmetry. Then, the vibrational analysis by using different techniques was determinant to the discussion in a supramolecular level.

Oxocarbons ions are cyclic compounds presenting unusual electronic and vibrational properties. These molecules anions possess a high symmetry and degree of electronic delocalization, characteristics that have been discussed in several structural and spectroscopic investigations. Compounds in which one or more of the carbonyl oxygen atoms are replaced by other atoms or groups are called pseudo-oxocarbons. Compounds formed by substitution of the carbonyl groups by nitrogen groups former a new class named squaraines. Specificity the dicyanomethylene groups are interesting because of the possibility of further extension of the electronic delocalization and a new coordination site. These molecules also present interesting coordination properties which make these systems potentially useful in crystal engineering research.