Interpenetration Transformation of Diacetylene Metal–Organic Frameworks for Topochemical Polymerization

Achieving precise control over topochemical polymerization in diacetylene metal-organic frameworks (MOFs) remains a huge challenge due to the stringent requirements for molecular alignment and ordered stacking. Herein, we report two interpenetrated MOFs (twofold interpenetrated CAS-20 and threefold interpenetrated CAS-22) from a diacetylene ligand and Zn nitrate, and systematically unveil their interpenetration transformation proceeds through dramatic changes with a set of non-interpenetrated semi-crystalline intermediates (CAS-20-d, CAS-21, CAS-21-d) accompanied by guest loss. This semi-crystalline state is driven by non-synchronous transformations of two individual frameworks in interpenetrated CAS-20, jointly revealed through crystallographic analysis and detailed spectroscopic characterization. Remarkably, this interpenetration transformation promotes the diacetylene groups arranged in a suitable ordered and continuous stacking manner, enabling thermally induced topochemical polymerization in CAS-22 via a 1,4-addition reaction. The results confirm that the obtained interpenetrated MOFs show classic nonlinear optical limiting performance, and the polymerized CAS-22 exhibits a remarkably enhanced third-order nonlinear absorption coefficient compared to CAS-20 (∼69 times). This study pioneers interpenetration transformation as a novel strategy for realizing MOF topochemical polymerization, opening new avenues for designing high-performance optoelectronic materials for smart sensing and laser protection applications.