Size-controlled synthesis and near-infrared photothermal response of Cp Rh-based metalla[2]catenanes and rectangular metallamacrocycles

A variety of research reports on novel supramolecular topologies have been published over the last years. However, it is still a great challenge to tap into the inner functional properties of these complexes. Herein, two tetranuclear metallamacrocycles 1 and 2 and four octonuclear [2]catenanes 3–6 were constructed successfully via a coordination-driven self-assembly strategy, by conscious design and use of the tetramethyl bidentate pyridine ligand L1, and the appropriate selection of six binuclear half-sandwich rhodium building units with different longitudinal dimensions. The complexes have been fully characterized by single crystal X-ray diffraction analysis and NMR spectroscopy. Furthermore, near-infrared photothermal studies of the obtained [2]catenanes reveal different photothermal response in solid and solution states, which may be attributed to a strong fluorescence quenching effect of the half-sandwich organometallic fragment and different conjugated effect of Cp*Rh based building blocks in the interlocking structures. The photothermal conversion efficiencies of [2]catenanes 4–6 fall in the range 30.5%–16.5% respectively. This contribution aims to play a key role in the experimental development of Cp*-based photothermal materials. Two types of supramolecular topologies: metallamacrocycles and metalla[2]catenanes were synthesized by selecting six Cp*Rh building blocks with different longitudinal sizes based on a 3,3′-N-donor pyridinyl ligand with strong electron-rich center. Besides, the discrepancy of building block size and strong conjugated effect result in huge difference of photothermal conversion of these interlocked complexes. [Display omitted]