Insights from electron density analysis into the charge transfer mechanism in a photoluminescent cocrystal of phenanthrene and tetrafluoro-1,4-benzoquinone

Abstract

Theoretical charge density studies are performed on the photoluminescent co-crystal of phenanthrene (PHNT) and tetrafluoro-1,4-benzoquinone (TFBQ) using the multipole modelling of theoretical structure factors. The topological analysis of the electron density is performed for all intramolecular covalent bonds and various important intermolecular interactions in the solid state. In addition to the presence of C-H...F interactions, the presence of aromatic stacking interactions has been confirmed via bond paths, topological properties and electrostatic potential isosurfaces of the electron density. The stacking interactions between the electron deficient and electron rich aromatic rings are demonstrated using the net atomic charges and electrostatic potential isosurfaces, which is responsible for the observed photoluminescent properties of the co-crystal. The molecular orbitals involved in the electronic transitions during UV-vis spectroscopic measurements have been identified and the electron density difference maps (EDDMs) arising from these transitions to different excited states have been plotted on isosurfaces which is in agreement with the Charge-Transfer (CT) nature of this co-crystal.