Enhancing Supramolecular Assembly in BODIPY Derivatives: Harnessing Halogen Bonding for Cocrystal Design

Abstract

Supramolecular synthesis, a field of study in chemistry, offers a versatile approach to construct complex structures using non-covalent interactions. In this study, we explore the use of halogen bonding (XB) to facilitate the co-crystallization of BODIPY structures with nitrogen-containing structures (XB acceptors), including 4-cyano-pyridine (4-CPY), 4,4'-bipyridine (4,4'- BPY), and hexamethylenetetramine (HTMA). The co-crystallization attempts with 3,4-diiodo-BODIPY (DIB) (with +19.4 kcal/mol s hole) were unsuccessful, probably due to low geometric accessibility. Therefore, we designed and synthesized 3,4-diiodoethynyl-BODIPY (DIEB) (with +31.0 kcal/mol s hole) to increase the size and geometric accessibility of s holes of iodine, which paved the way for successful synthesis of the co-crystals of BODIPY derivatives [4-CPY-DIEB, 4,4'- BPY-DIEB, and HTMA-(DIEB)(2)]. The single crystal analyses showed that 4-CPY-DIEB and 4,4'- BPY-DIEB formed one-dimensional (1D) chain structures, whereas HTMA-(DIEB)2 formed a diamondoid-like three-dimensional (3D) architecture with five-fold interpenetration. The symmetry-adapted perturbation theory (SAPT) analysis showed that the XB formations are mainly driven by electrostatic forces. This work represents the first report of successful cocrystal synthesis of BODIPY derivatives and thereby clearing the path for the exploration and development of highly intricate functional materials utilizing the remarkable properties of BODIPY.