Reversible pH‐Controlled Catenation of a Benzobisimidazole‐Based Tetranuclear Rectangle

Abstract

The development of methodologies to control on demand and reversibly supramolecular transformations from self-assembled metalla-structures requires the rational design of architectures able to answer to an applied stimulus. While solvent or concentration changes, light exposure or addition of a chemical have been largely explored to provide these transformations, the case of pH sensitive materials is less described. Herein, we report the first example of a pH-triggered dissociation of a coordination-driven self-assembled interlocked molecular link. It incorporates a pH sensitive benzobisimidazole-based ligand that can be selectively protonated on its bisimidazole moieties. This generates intermolecular electrostatic repulsions that reduces drastically the stability of the interlocked structure, leading to its dissociation without any sign of protonation of the pyridine moieties involved in the coordination bonds. Importantly, the dissociation process is reversible through addition of a base.

Transformation networks of metal–organic cages controlled by chemical stimuli

“…In this review, we detail transformations between discrete architectures, where at least one of the species in the network is a three-dimensional metal-organic cage. Novel examples of transformations involving other types of self-assembled structures, 42 including helicates, 43,44 macrocycles, 45,46 other one-and two-dimensional assemblies, 47,48 and extended structures 49 such as metal-organic frameworks, 50 metallopolymers [51][52][53] and soft materials, 54 fall beyond the scope of this review. As others 41 and our group 40 have recently reviewed strategies to covalently modify coordination assemblies after their formation, we do not treat this type of chemical transformation herein.…”

Switchable metallacycles and metallacages

“…74 A recent study by Goeb et al involved reversible pH-triggered catenation based on switchable metallacycles. 75 In their work, metallacycle 53 was constructed through the self-assembly of pH-sensitive benzobisimidazole-based ligand 51 and bis-ruthenium acceptor 52 , followed by a catenation process to generate interpenetrated catenane 54 at a high concentration (Scheme 1). Due to the presence of pH-sensitive imidazole units, when the pH value was decreased, nonprotonated metallacycle 53 underwent a stepwise protonation instead of disassembly to produce protonated metallacycle 55 , destroying catenation by electrostatic repulsion effects.…”

Fluorescent cyclophanes and their applications

“…This behaviour has been attributed to the effect of temperature on the degree of concerted rotation of pendant anthracene units in 89 . Luminescent metallocyclophanes have also been employed in sensing, 221 DNA binding, 222 cell imaging, 222 a , c and biomedical 223 applications, as well as in the formation of catenanes 224 and supramolecular assemblies. 225 It follows that the investigation of fluorescent metallocyclophanes is of key importance in light of the various possible applications derived from them.…”

“…The complexity of MIMs, along with the advantages of fluorescent cyclophanes, enable the creation of highly inventive systems. Therefore, many catenanes, 224,325 rotaxanes 326 and some knotted macrocycles 136,327 displaying luminescent properties originating from their cyclophanes have been described in the literature.…”