Structural and thermochemical properties of a photoresponsive spiropyran and merocyanine pair: Basis set and solvent dependence in density functional predictions

► Lower energetic splitting between SP & MC isomers when using a larger DFT basis set. ► MC conformers strongly stabilized in solvents, their dipole moments enhanced than SP. ► Partial atomic charges & bond lengths predict quinoid and not zwitterionic form for MC. ► The more flexible MC forms have higher entropies & lower free energies than in SP.