The role of intramolecular interactions on the stability of the conformers of a spiropyran derivative

Abstract

DFT level calculations of the thermal isomerization reaction of SP ⇋ MC, in which SP is the spiropyrans derivative 3-(3′,3′-dimethyl-6-nitrospiro[chromene-2,2′-indole]-1′-yl) propanoic acid in the closed-form and MC (merocyanine) is the corresponding open form. An extensively theoretical analysis of the reaction is reported alongside thermodynamics. Scan calculations considered the influence of the carboxyl acid group. Solvents were treated implicitly, and their effects on the MC isomers' geometries, thermodynamics, and electronic parameters were determined. Among several calculated results in good agreement with experimental data, one, in particular, is the description of an intramolecular hydrogen bond in the most stable MC isomer by using the Reduced Density Gradient (RDG) method to perform non-covalent interactions analysis. These results allowed us to evaluate, qualitative and quantitatively, the role of intramolecular interactions in the stability of the structures providing novel results for a better understanding of the complex thermal isomerization process of the spiropyrans.