Theoretical investigation of the isomerisation of merocyanine

The isomerisation of two isomers of merocyanine, is examined using time-dependent density functional theory with modern functionals. Using an implementation of the branch plane updating algorithm of Maeda et al., a conical intersection which connects the excited state and ground-state structures of these isomers has been identified. The presence of this conical intersection and the general flatness of the excited state surface confirms the ease of interconversion between the two isomers as found by experiment.