Pseudo Jahn-Teller origin of instability of planar configurations of hexa-heterocycles. Application to compounds with 1,2- and 1,4-C4X2 skeletons (X = O, S, Se, Te)

Abstract

The driving force of symmetry breaking in planar molecular-ring systems in nondegenerate states is the pseudo Jahn-Teller effect (PJTE), and the knowledge of the mechanism of the latter allows one to manipulate the molecular properties, in particular, by restoring the planar configuration. We explore the PJTE induced structural nonplanarity in a series of 12 hexa-heterocycles with a C4X2 skeleton, 1,2- and 1,4-dichalcogenins with X=O, S, Se, Te, and a variety of ligands (H, F, Cl, Br). All the structures are optimized in both distorted equilibrium and unstable planar configurations, and the vibrational frequencies of the latter are evaluated. Then the energy profiles of the ground and several excited states in the planar configuration along the coordinate of instability are calculated, the excited states producing the instability of the ground state via the PJTE are revealed, and the vibronic coupling constants are estimated by means of fitting the solutions of the secular equations to the corresponding energy profiles.