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

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.