Role-Allocated Combination of Two Types of Hydrogen Bonds towards Constructing a Breathing Diamondoid Porous Organic Salt

A diamondoid porous organic salt (d-POS) composed of 8-hydroxyquinoline-5-sulfonic acid (HQS) and triphenylmethylamine (TPMA) shows reversible structure contraction and expansion (breathing) in response to guest desorption and adsorption. This flexible structure is designed hierarchically by utilizing two different types of hydrogen bonds. X-ray crystallographic analysis reveals that the two types of hydrogen bonds are formed separately to play respective roles for constructing the d-POS. The strong charge-assisted hydrogen bond between the sulfonate anion of HQS and the ammonium cation of TPMA serves as a static node to provide a supramolecular cluster for a building block. In contrast, the complementary neutral hydrogen bond between the hydroxyl and quinolyl groups of HQS acts as a dynamic linker to connect the clusters. Consequently, these two types of hydrogen bonds yield the d-POS with one-dimensional channels through the formation of diamondoid networks. We clarify that the d-POS undergoes dynamic structure transformation that originates in the cleavage and reformation of the complementary neutral hydrogen bond during guest desorption and adsorption. From the comparative studies, it is also demonstrated that applying the complementary neutral hydrogen bond in the d-POS provides significant advantages in terms of the responsivity of the structure over applying other weak noncovalent interactions for the connection of the clusters. Furthermore, the resultant d-POS also modulates fluorescent profiles dynamically responsive to guest adsorption and desorption.