From π-conjugated macrocycles to heterocycloarenes based on benzo[2,1-b:3,4-b′]dithiophene (BDTh): size- and geometry-dependent host–guest properties

Abstract

π-Conjugated macrocycles have been highly attractive due to their challenging synthesis, fascinating aesthetic structure and unique physical and chemical properties. Although some progress has been made in synthesis, the study of π-macrocycles with different structural characteristics and supramolecular interactions still faces major challenges. In this paper, two new single-bond linked macrocycles (MS-4T/MS-6T) were reported, and the corresponding vinyl-bridged heterocycloarenes (MF-4T/MF-6T) were synthesized by the periphery fusion strategy. Further studies have indicated that the structure of these four macrocycles is determined by both size and curvature, showing unique variations from nearly planar to bowl and then to saddle. Interestingly, the nearly planar MS-4T with a small size and the rigid saddle-shaped MF-6T show no obvious response to fullerenes C₆₀ or C₇₀, while the bowl-shaped MS-6T and MF-4T demonstrate a strong binding affinity towards fullerenes C₆₀ and C₇₀. What's more, two kinds of co-crystals with capsule-like configurations, MS-6T@C₆₀ and MS-6T@C₇₀, have been successfully obtained, among which the former shows a loose columnar arrangement while the latter displays a unique three-dimensional honeycomb arrangement that is extremely rare in supramolecular complexes. This work systematically studies the π-conjugated macrocycles and provides a new idea for the development of novel host–guest systems and further multifunctional applications.