Controlled Assemblies of Multistacked [2]Catenanes with Azo-Conjugated Branched Chain for Enhanced Photothermal...

The strategic design and performance improvement of mechanically interlocked topological structures become a fascinating challenge. In this work, a bidentate pyridyl ligand (L1), which possesses a conformationally flexible azo-conjugated branched chain, is selected under rational design. Through the coordination-driven self-assembly strategy─by modulating the Rh-Rh distance and the steric hindrance of the conjugated plane in the building unit and adjusting the solution concentration─we successfully access a pair of metallamacrocycle isomers 1, 1', two [2]catenanes 2, 3, and one metallamacrocycle 4 with various multiple stacking. All supramolecular compounds are unambiguously characterized using single-crystal X-ray diffraction (SC-XRD), nuclear magnetic resonance (NMR) spectroscopy, and electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS). The distinct π···π stacking patterns and varying organic radical effects are exhibited by these compounds. These findings prompted the evaluation of the photothermal performance of compounds 1-4. The results show that multiple π···π stacking interactions significantly enhance their photothermal performance. Furthermore, compound 2 exhibits a photothermal conversion efficiency ranging from 73.8% to 75.6%. Moreover, the electron paramagnetic resonance (EPR) measurements reveal that the photogenerated organic radicals from the building units also contribute to the enhanced photothermal conversion performance, a finding that suggests a promising strategy for designing efficient photothermal materials.