Intrinsic Near-Infrared Photothermal Effect Induces Single-Crystal-to-Single-Crystal Transformation in Organic Molecular Crystals.

Near-infrared (NIR) light-driven single-crystal-to-single-crystal (SCSC) transformation holds profound significance for supramolecular chemistry and smart materials, yet remains a formidable challenge in purely organic molecular crystals. Herein, we demonstrate SCSC transformation driven by the intrinsic NIR photothermal effect of a rationally designed croconium derivative CR-DPA-OMe, which features strong NIR absorption and a high photothermal conversion efficiency of 60%. Solvated CR-DPA-OMe single crystals encapsulating CHCl3 molecules exhibit exceptional ambient stability with crystallinity preserved for over two years. Benefiting from the robust dimeric packing of croconium motifs and the conformationally flexible methoxy-substituted diphenylamine moieties, the resulting crystals successfully reconcile long-range lattice order with structural flexibility, thus enabling efficient SCSC transformation upon NIR photothermal stimulation. Combined density functional theory (DFT) calculations and in situ single-crystal x-ray diffraction analysis confirm that the transformation is driven by the synergistic interplay of photoinduced molecular conformational reorganization and photothermally-converted heat, affording markedly faster transformation than conventional oven heating. Furthermore, tailored NIR irradiation enables spatiotemporally programmable guest release, demonstrating a remote manipulation inaccessible via macroscopic conductive heating. These findings highlight the substantial promise of NIR photothermal modulation as an emerging stimuli-responsive strategy for precise structural engineering in molecular crystals, opening new avenues toward tailored functional material applications.