Crystal Growth, Intermolecular Noncovalent Interactions, and Photoluminescence Properties of Halogenated Phthalic Anhydride-Based Organic Charge Transfer Cocrystals

Organic charge-transfer cocrystals are composed of an electron-rich donor molecule and an electron-deficient acceptor molecule, which are bonded together by intermolecular noncovalent interactions such as π–π interactions, hydrogen bonds, halogen bonds, and charge-transfer interactions. These noncovalent interactions influence the cocrystal packing structures and the photoluminescence properties. Herein, four charge transfer cocrystals, pyrene-tetrafluorophthalic anhydride (TFPA), perylene-TFPA, pyrene-tetrachlorophthalic anhydride (TCPA), and perylene-TCPA, were grown by the slow cooling method and the influence of intermolecular noncovalent interactions on the photoluminescence properties were investigated. Cocrystals of pyrene-TFPA and pyrene-TCPA exhibit a yellow rod-like morphology, while both perylene-TFPA and perylene-TCPA exhibit red rod-like shapes. Results indicate that the C–H···X (X = F, Cl, or O) interactions, π–π interactions, and charge-transfer interactions are dramatically affected by the energy difference between the HOMO of the donor and the LUMO of the acceptor. Meanwhile, for the same acceptor molecules, the positions of the photoluminescence peaks of the cocrystals red-shifted with the enhancement of weak noncovalent interactions, which paved the way to tuning the optical properties of charge transfer cocrystals.