Efficient synthesis of a snowflake-shaped folded assembly, an 818 knot, and a closed three-link chain via coordination angle modulation

Abstract Despite the appeal of mechanically interlocked supramolecular systems, precise control over their assembly into complicated topologies is still a central challenge. To address this, we employed a method centered on regulating the coordination angle. By designing two ligands (L1 and L2) with differing carbazole-pyridine connection angles and combining them with tailored building units E1(OTf)2 and E2(OTf)2, we successfully directed the synthesis of four unique architectures: a molecular-tweezer-like compound, a snowflake-shaped folded assembly, an 818 knot, and a closed three-link chain. Single-crystal X-ray diffraction (SC-XRD) analysis provided unambiguous structural elucidation, not only confirming the three-dimensional geometries but also revealing that the ligand angle dictates the outcome of assembly, steering it toward interlocked or folded structures. The formation and purity of these constructs in solution were verified by nuclear magnetic resonance (NMR) spectroscopy and electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS). Furthermore, photothermal conversion experiments demonstrated that compound 4(OTf)12 exhibits favorable photothermal performance, with a relatively higher photothermal conversion efficiency as well as excellent cycling stability. This observation is also supported by electron paramagnetic resonance (EPR) measurement data.