Ab initio investigation of the structures and energies of spiropyran and merocyanine isomers

The structures and energies of a set of spiropyrans and merocyanines – BIPS [1′,3′,3′-trimethylspiro[2H-1-benzopyran-2,2′-indoline], 6-nitroBIPS, and 6,8-dinitroBIPS – are calculated using density functional theory and second-order Møller–Plesset methods. The relative energies of all possible merocyanine isomers in the ground state are determined systematically at a uniform level of theory. Solvent contributions, which have been found to be significant, are also included.