Mechanically interlocked molecules (MIMs) can be conceptualized as a distinct class of discrete and soluble aggregates, where the mechanical bond restricts selected intramolecular motions, thereby triggering emission enhancement analogous to aggregation-induced emission (AIE). Herein, we present phosphorescent MIMs based on a benzobiscarbene bridged dinuclear PtII complex (NHC = N-heterocyclic carbene ligand). Tailoring the N-substituents of the benzobiscarbene ligand allowed selective access to the syn-configured dinuclear complex syn-Pt2(1b)X2 (X = I, OTf). Self-assembly of syn-Pt2(1b)(OTf)2 with bipyridyl ligands L2 and L3 yielded two discrete MIMs: the Borromean rings 2-BRs(OTf)12 stabilized by π···π interactions and the 2catenane 3b-IL(OTf)4, generated and stabilized by solvophobic effects. While the π···π interactions in the Borromean rings lead to severe phosphorescence quenching, the solvophobically assembled 2catenane effectively circumvents such quenching, while simultaneously restricting intramolecular rotations and vibrations. Consequently, the 2catenane displays a drastic phosphorescence enhancement compared to the Borromean rings.
Lu et al. (Mon,) studied this question.