Stimuli-Responsive Dynamics and Structural Adaptability in a Coordination Framework Enabling Rapid Photothermal Conversion

Abstract

The entanglement of stimuli-responsive structural dynamics and intrinsic framework adaptability governs diverse single-crystal-to-single-crystal (SCSC) transformations in crystalline coordination frameworks, endowing them with desirable physicochemical properties. Herein, two fluorene-based ligands, 9,9-diethyl-9H-fluorene-2,7-dicarboxylic acid (H2L1) and 4,4'-(9,9-diethyl-9H-fluorene-2,7-diyl)dipyridine (L2), are utilized to assemble a flexible three-dimensional 3-fold interpenetrated coordination framework, [Co2(L1)2(L2)]n (NBU-X3). Single-crystal X-ray diffraction demonstrates two distinct SCSC transformation pathways among three phases of NBU-X3. Removal of guest molecules from the framework triggers a stimuli-responsive structural reorganization upon thermal treatment. Although solvent exchange induces distortions in the building units of framework, including metal clusters and organic ligands, the overall framework packing remains intact with the dominant role of intrinsic structural adaptability. Solvent-free samples exhibit stable photothermal conversion performance over multiple cycles, reaching 324 °C within 2 s and stabilizing at 364 °C within 10 s under 808 nm laser irradiation (1.9 W cm−2). The photothermal response enables practical applications such as the thermal initiation of paper combustion.