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 <b>1</b>, composed of three BODIPY units linked by <i>m</i>-phenylene spacers. Two dynamic conformers of <b>1</b>, namely, cone-shaped <i>c</i>-<b>1</b> and partial-cone-shaped <i>pc</i>-<b>1</b>, 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 <i>c</i>-<b>1</b> 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 <i>pc</i>-<b>1</b>. Crystallization conditions were optimized, enabling the preparation of gram-scale crystals of <i>c</i>-<b>1</b> with different packing arrangements, designated as <i>c</i>-<b>1a</b> and <i>c</i>-<b>1b</b>. Activation of these two samples led to transformations from single-crystal to single-crystal or to amorphous, yielding crystalline <i>c</i>-<b>1a'</b> and amorphous <i>c</i>-<b>1b'</b>, respectively. Importantly, crystalline <i>c</i>-<b>1a'</b> exhibits excellent adsorption capacity and separation selectivity for hydrogen isotopes, benefiting from its permanent ultramicroporosity. In contrast, amorphous <i>c</i>-<b>1b'</b> 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.