Resumo:
Spiropyrans (SP) isomerize to merocyanines (MC) when exposed to external factors such as radiation, temperature changes, different solvents, etc. The phenomenon that focuses on the influence of the solvent on changing electronic properties is called solvatochromism and can be observed by the change in color of a solution with the same solute in different solvents. In this study we started from a system containing an isomer of merocyanine, MC-TTC, in methanol solution, to verify the electronic interactions that explain this phenomenon.
Computational chemistry was first used with the Gaussian 09 software, applying Density Functional Theory (DFT), carrying out simulations in the liquid phase implicitly, using the IEFPCM method. Geometry optimization, vibrational frequency and atomic charge calculations were performed with the M06-2X functional and 6-31G(d,p) basis function. With the results obtained, the simulations were followed explicitly.
Using classical mechanics, Monte Carlo simulations were considered for explicit solvation, in which the DICE 3.0 software represented the solute-solvent system considering an NPT ensemble and OPLS force field. As result, radial distribution function was obtained, defining the distance and quantity of methanol in the solvation shells (1st: 8 molecules; 2nd: 17 molecules), as well as atom-atom interactions. In these, the behavior of the solvent distributions and its highest concentration in certain regions were predicted.
Fifty statistically uncorrelated configurations were selected, directing them to quantum calculations using the TD-DFT methodology. At this stage, the M06-2X functional and 6-31G(d,p) base function were maintained, such as the IEFPCM method, to represent long-distance interactions. UV-Vis spectra were generated, where a significant difference of approximately 40 nm was found between the maximum absorption values of these 50 configurations. The same analysis was carried out for the second solvation shell, and, as a summary of the results, it was confirmed that the explicit representation is efficient in presenting the phenomenon of solvatochromism, and consequently, in understanding the factors that influence solute-solvent interactions.
