Density functional theory study of the trans-trans-cis (TTC)-->trans-trans-trans (TTT) isomerization of a photochromic spiropyran merocyanine.

Density Functional Theory (DFT) calculations have been performed on the TTC-->TTT isomerization reaction of the open forms of the 1',3'-dihydro-8-bromo-6-nitro-1',3',3'-trimethylspiro[2H-1-benzopyran-2,2'-(2H)indole (8-Br-6-nitro-BIPS) system. The calculations were carried out in vacuo and in methylene chloride solution at different temperatures. Results are compared with the available experimental values of free energy difference and activation energy in solution.