Quantum chemical studies of photochromic properties of benzoxazine compound

Molecular electronic structure of ground and excited states of a photochromic indolo[2,1-b][1,3]benzoxazine compound incorporating closed-ring system, which opens upon UV light excitation, was studied using various quantum chemical methods. Three local minima of the ground electronic state potential energy surface and related transition states were identified along the path of rotation of 4-nitrophenol group. Additionally, three local minima of the excited electronic states were located. The evaluated transition energy barriers between local ground-state minima nearest to the initial structure of the investigated molecule are less than 2 kBT, making open structures likely to revert to the initial structure by thermalization. Results obtained using ab initio GMC-QDPT method were explored and compared to the widely used TD-DFT and semi-empiric ZINDO methods.

Highlights► Photochromic indolo-benzoxazine compound is studied. ► Advanced LC-TDDFT and GMC-QDPT methods are used for excited state calculations. ► Oxazine ring opens upon UV light excitation. ► Fragments of the compound assume structures similar to the ions of separate molecules. ► Multiple pathways of the photo-induced reaction are expected.