Guest-induced topological transformation and near-infrared photothermal conversion featuring the Cp*Rh unit via coordination-driven self-assembly

Herein, we perform a topological transformation by guest induction, converting [2]catenane Rh-1 into the Rh-3 molecular figure-of-eight. The transformation involves the interaction of longer π-acceptor half-sandwich Rh^III bimetallic building block B1 [(Cp*Rh)₂(TPPHZ)](OTf)₄ and π-donor bipyridyl ligands 4,4′-bis((pyridin-4-ylthio)methyl)-1,1′-biphenyl with four molecules of pyrene under ambient temperature in high yields. Intriguingly, despite the involvement of a single pyrene molecule in modifying [2]catenane Rh-2 by transitioning B1 to B2, the underlying skeleton of Rh-2 remains unaltered. Furthermore, we explored the application of these substances before and after the reaction for near-infrared (NIR) photothermal conversion. Through meticulous structural analysis, the π–π stacking interactions play a pivotal role in stabilizing the abovementioned structures, enhancing the nonradiative transitions and initiating photothermal conversion in solution. Based on the results, the introduction of pyrene significantly intensified the π–π stacking interactions but diminished the electron density between the adjacent NDI units, leading to a decrease in the NIR photothermal conversion efficiency (from 58.29% to 51.60%). In this study, an innovative approach is introduced for fabricating valuable half-sandwich-structured NIR photothermal conversion materials, and this research has promising prospects for enhancing the field of materials science with potential candidates for future development.