Copper Diphosphonate Frameworks Incorporating Dianthracene: Capture of a Metastable Intermediate, Framework Transformation, and Near-Infrared Photothermal Properties.

The crystallization pathways of metal phosphonate frameworks (MPFs) remain poorly understood because the strong coordination ability of phosphonate ligands often leads to rapid precipitation, making the isolation of transient intermediates challenging. Herein, we report two 3D Cu-based MPFs, [Cu2(amp2H2)]·2H2O·DMF (Cu-3D) and [Cu2(INA)2(amp2H2)(H2O)2] (Cu-INA-3D), where amp2H4 is photodimerized 9-anthracenemethylphosphonic acid and INAH is isonicotinic acid. By shortening the reaction time, we isolated a metastable intermediate, [Cu2(INA)2(amp2H2)]·2H2O (Cu-INA-2D), which can gradually transform into the thermodynamically more stable Cu-INA-3D phase via reconstruction of the Cu-PO3 connectivity and reorganization of the {Cu(INA)} chains. The crystals of Cu-INA-2D can undergo solvent-assisted cleavage to yield an accordion-like morphology. Further, thermal de-dimerization of the dianthracene units in Cu-3D and Cu-INA-3D induces framework transformation, generating new phases containing anthracene moieties. We studied the photothermal properties of Cu-3D, Cu-INA-3D and their de-dimerized products. All exhibited near-infrared (NIR) photothermal responses under 808 nm laser irradiation. Benefiting from its photothermal conversion capability and the redox activity of CuII centers, Cu-INA-3D was employed to serve as a photothermally driven catalyst for pyrrole polymerization. These findings provide insight into the crystallization mechanism of copper diphosphonate frameworks and demonstrate the potential of dianthracene-based MPFs as multifunctional photothermal materials.