Development of fluorophoric [2]pseudorotaxanes and [2]rotaxane: selective sensing of Zn(II)

From construction to application of a new generation of interlocked molecules composed of heteroditopic wheels

Over the last few decades, research on mechanically interlocked molecules has significantly evolved owing to their unique structural features and interesting properties. A substantial percentage of the reported works have focused on the synthetic strategies, leading to the preparation of functional MIMs for their applications in the chemical, materials, and biomedical sciences. Importantly, various macrocyclic wheels with specific heteroditopicity (including phenanthroline, amide, amine, oxy-ether, isophthalamide, calixarene and triazole) and threading axles (bipyridine, phenanthroline, pyridinium, triazolium, etc.) have been designed to synthesize targeted multifunctional mononuclear/multinuclear pseudorotaxanes, rotaxanes and catenanes. The structural uniqueness of these interlocked systems is advantageous owing to the presence of mechanical bonds with specific three-dimensional cavities. Furthermore, their multi-functionalities and preorganised structural entities exhibit a high potential for versatile applications, like switching, shuttling, dynamic properties, recognition and sensing. In this feature article, we describe some of the most recent advances in the construction and chemical behaviour of a new generation of interlocked molecules, primarily focusing on heteroditopic wheels and their applications in different directions of the modern research area. Furthermore, we outline the future prospects and significant perspectives of the new generation heteroditopic wheel based interlocked molecules in different emerging areas of science.

NDI-integrated rotaxane/catenane and their interactions with anions

Complexation of alkali and alkaline earth metal ions with the heteroditopic Phen-ester oxy-ether macrocyclic wheel (PhenMC) is established for the synthesis of interlocked molecular systems. The single crystal X-ray structure of Na-bound PhenMC confirms the hexacoordinated geometry around the Na ion in the macrocycle. Further, Ca-ion-bound PhenMC (Ca-PhenMC) is explored with a fluorophoric azide-terminated NDI (naphthalene diimide) axle (NDIAz) for the synthesis of fluorophoric [2]rotaxane (NDIROT) and [2]catenane (NDICAT) via Cu(I)-catalyzed cycloaddition reaction. Characterizations of these two new interlocked molecular systems are performed by ESI-MS, NMR, UV-vis and PL spectroscopic studies wherever applicable. Moreover, the new molecular systems are explored towards anion sensing applications via colorimetric, UV-vis-NIR, PL and other spectroscopic studies.