Cyclic BODIPY Arrays: A Class of Macrocycle-Based Molecular Solids for Hydrogen Isotope Separation and Iodine Capture

Abstract

Macrocyclic hosts are pivotal in supramolecular chemistry, yet the discovery of synthetically scalable platforms that combine rich host–guest behavior, facile crystallizability, and solid-state functionality remains a challenge. Here, we present the synthesis of a new cyclic BODIPY array, trimer 1, composed of three BODIPY units linked by m-phenylene spacers. Two dynamic conformers of 1, namely, cone-shaped c-1 and partial-cone-shaped pc-1, exist in solution and have been characterized by their X-ray crystal structures. These two conformers undergo interconversion in response to changes in external environments, including solvents and guests. Conformer c-1 is capable of hosting neutral guests bearing electron-deficient methyl groups in solution, driven by collective C–H···F interactions, while cationic guests with ammonium groups are preferentially hosted by conformer pc-1. Crystallization conditions were optimized, enabling the preparation of gram-scale crystals of c-1 with different packing arrangements, designated as c-1a and c-1b. Activation of these two samples led to transformations from single-crystal to single-crystal or to amorphous, yielding crystalline c-1a′ and amorphous c-1b′, respectively. Importantly, crystalline c-1a′ exhibits excellent adsorption capacity and separation selectivity for hydrogen isotopes, benefiting from its permanent ultramicroporosity. In contrast, amorphous c-1b′ is an effective adsorbent for molecular iodine, with binding interactions fully elucidated through X-ray crystallographic analysis. This work establishes cyclic BODIPY arrays as a highly tunable platform for creating adaptive molecular solids with applications in separation science, moving beyond their inherent optical properties.