Abstract
Hoop-shaped or belt-like molecules have been fascinating not only due to their challenging synthesis, but also unique physical and chemical properties. The incorporation of heteroatoms (N, O, S, etc.) into these belts could alter both molecular structures and electronic properties which will lead to versatile applications, from advanced host-guest systems to functional materials. Despite numerous computational studies, the synthesis and characterization of heteroatom-bridged double-stranded molecular belts remains scarce. Here we report the synthesis, crystal structure, and host-guest chemistry of two novel heteroatom-bridged belt-like macrocycles composed of phenoxathiin. The bowl-shaped belt demonstrates a strong binding affinity (Ka = 3.6 × 109 M‒2) towards fullerene C60 and forms a 2:1 capsule-like complex with the aid of C‒H···S hydrogen bonds. The column-like belt can bind the cyclic guest [2,2]paracyclophane to form a ring-in-ring complex. The modular synthesis, structural specificity, and diverse host-guest chemistry of cyclophenoxathiins markedly expands the known chemistry of molecular belts.
Highlights
Hoop-shaped or belt-like molecules have been fascinating due to their challenging synthesis, and unique physical and chemical properties
The cyclization of subunits with double linkages has been shown to result in molecular belts or Möbius strips14, and the synthesis of all carbon nanobelts could enable the bottom-up synthesis of carbon nanotubes15
Despite the numerous theoretical studies20, there are few reported belt-like macrocycles with double-heteroatom bridges that are constructed via this synthetic method21,22. This strategy has been successfully applied to synthesis of polymers, including the phenoxathiin-based polyheteroacenes23
Summary
Hoop-shaped or belt-like molecules have been fascinating due to their challenging synthesis, and unique physical and chemical properties. A number of wellestablished families of synthetic macrocycles, including calixarenes, calixpyrroles, resorcinarenes, pillararenes, coronarenes, cyclophanes, and cycloparaphenylenes (CPPs), have found applications in the fabrication of diverse supramolecular architectures, and have led to advanced systems for sensing, adsorption/separation, drug delivery, and molecular machines. A number of wellestablished families of synthetic macrocycles, including calixarenes, calixpyrroles, resorcinarenes, pillararenes, coronarenes, cyclophanes, and cycloparaphenylenes (CPPs), have found applications in the fabrication of diverse supramolecular architectures, and have led to advanced systems for sensing, adsorption/separation, drug delivery, and molecular machines12 These macrocycles are singly bridged entities—those with repeating units linked via a single-bond bridge. Despite the numerous theoretical studies, there are few reported belt-like macrocycles with double-heteroatom bridges that are constructed via this synthetic method21,22 This strategy has been successfully applied to synthesis of polymers, including the phenoxathiin-based polyheteroacenes. We report the first synthesis, structures, and host–guest chemistry of two unique doubly bridged belt-like macrocycles, i.e., cyclo[8] phenoxathiins
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