Transition Energy, Spectral Fine Structure, and Absorption Coefficient of Norbixin (9'-cis-6,6'-diapocarotene-6,6'dioic acid) in Different Polar Solvents

Abstract

Transition energy, spectral fine structure, and absorption coefficient of norbixin in different polar solvents has been investigated. Eight polar solvents were used for dissolving norbixin separately, including methanol, ethanol, propylene carbonate, acetone, dichloromethane, ethyl acetate, chloroform, and dimethyl carbonate. Spectra of norbixin in the resulting solutions were determined by UV-visible spectrophotometry at atmosphere condition. The effect of solvents on transition energy was analyzed according to Onsager cavity model and Hansen theory. The approximate absorption coefficient was determined with the Beer-Lambert law. The result show that the UV-visible absorption spectra of norbixin depend onz the solvent. The greater the refraction index of the solvent and the norbixin-solvent dispersion interaction cause the transition energy of norbixin was smaller. The change in spectral fine structure has some relevance or correlation with the solvatochromic effect on π → π∗ transitions, the intermolecular interactions, and the S2 state of norbixin. The absorbance of norbixin in various solvents, increased linearly with concentration.