Estudo teórico computacional do corante Solvent Blue 22 e dos efeitos de substituições no seu anel Fenilênico

Abstract

A colo ring substance has one or more chromophores that absorb light radiation in the UV VIS range, the visualized color corresponds to the wavelength complementary to the absorbed one and can be satisfactorily estimated by Woodward Fieser Roules when the structu re presents planarity and absorption core with π π * transitions. Compounds that present chromophores with electronic promotion of the n π * type require specific studies to estimate color and/or properties. The Solvent Blue 22 dye is an example, in addition to the n π * and π π * transitions, the azomethine group allows the ring rotation of the phenylene part, allowing the occurrence of conformers with greater or lesser color intensity within the blue hue. . This work computationally studied different structur es resulting from the Solvent Blue 22 dye with the objective of determining the accuracy of the results between the calculated and the experimental λ max for some Pople bases sets, identifying the guiding factor of the bathochromia for three substituted ver sions and proposing a methodology for estimate of the observed color. Among the results, it was identified that the smallest relative variation for λ max was 0.28%, obtained with the Continuous Polarizable Model (PCM) and TD DFT/B3LYP/6 311G(d). In this sit uation, an increase in the polarity of the molecule and an increase in the charge density on the chromophore region were observed, when compared to the study in vacuum and in the formation of a cluster with methanol. The existence of rotational barriers re sults in two lower energy conformations in each version with different absorption and properties. The most stable conformers for the standard structure (X=H) and for the substitutions (X=Cl, X=CH3 and X=OCH2CH3 ), show bathochromy with the loss of planarit y, that is, with the reduction of the π system extension. The calculated absorption peaks ( λ max) of 562, 572, 578 and 576 nm for the standard structure and for the substitutions with chlorine, methyl and ethoxy respectively, are smaller than the experiment al ones, intensifying the blue tones in the RGB scale, when compared to the estimated with the experimental values. In conclusion, the color of Solvent Blue 22 can be adjusted by controlling the twist between rings with alkyl or aryl substituent groups. Fo r the halogenated substituents, a specific study should be carried out since the substitution with Cl presented divergent results from the others.