The Selective Synthesis and Photothermal Conversion Properties of U- and S-Shaped Flexible Double-Metallacycle...

Molecular double-metallacycles have drawn considerable interest for their unique architectures and broad application prospects, yet selective synthesis remains a significant challenge. This work reports a novel triimidazolyl flexible ligand precursor L1 containing a phenyl unit with three methyl groups and three methylene spacers that enable flexibility for the coordination of imidazole units. Together with three half-sandwich rhodium building blocks (B1-B3) of varying conjugation sizes, L1 was assembled via coordination-driven self-assembly and silver-ion bridging to afford one U-shaped and two S-shaped double-metallacycles in high yields. The greater steric demand of B2 and B3 favored the S-shaped topology. The formation of all target structures was clearly confirmed by SC-XRD (Single-crystal x-ray diffraction analysis), NMR (Nuclear magnetic resonance) spectroscopy, IR (Infrared) spectroscopy, and ESI-TOF-MS (Electrospray Ionization-Time of Flight Mass) spectrometry. TGA (Thermogravimetric analysis) indicated good thermal stability for compounds 1-3. Photothermal conversion experiments revealed that S-shaped double-metallacycle 3 achieves notable photothermal conversion efficiency (21.46%-22.95%) in the NlR (near-infrared) region. EPR (Electron paramagnetic resonance) studies further corroborated that radical generation from the building blocks enhances photothermal performance.