Exploring the Relationship between Intermolecular Interactions and Solid-State Photophysical Properties of Organic Co-Crystals

Abstract

Five new binary co-crystals have been prepared through molecular self-assembly of π-electron-rich molecules, such as phenanthrene, benzo[c]cinnoline, and phenazine, in the presence of π-electron-deficient molecules, such as tetrafluoro-1,4-benzoquinone, tetrachloro-1,4-benzoquinone, and 1,2,4,5-tetracyanobenzene, taken in an equimolar ratio. Crystal structure analysis revealed that in three binary co-crystals the constituent molecules were alternately sandwiched in a cofacial arrangement through π···π interactions, whereas in the remaining two binary co-crystals the constituent molecules were aligned in a unique edge-to-face manner through lp···π interactions. Co-crystals with π-stacking arrangement were fluorescent, whereas almost complete quenching of luminescence was observed in those having edge-to-face alignment of molecules. The photophysical observations of these co-crystals have been demonstrated via energetic quantification of the intermolecular interaction topology, which provides a molecular level understanding of factors controlling their solid-state absorption and luminescence behavior.