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Corralarenes: A Family of Conjugated Tubular Hosts

       Han Han,^1,2 Rong Fu,¹ Ruiguo Wang,¹ Chun Tang,² Miao-Miao He,¹ Jia-Ying Deng,¹ Dong-Sheng Guo,¹ J. Fraser Stoddart,^2,3,4,5 Kang Cai¹*

        ¹College of Chemistry, Nankai University, 94 Weijin Road, Tianjin 300072, China

        ²Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States

        ³ Stoddart Institute of Molecular Science, Department of Chemistry, Zhejiang University, Hangzhou 310027, China

        ⁴ZJU-Hangzhou Global Scientific and Technological Innovation Center, Hangzhou 311215, China

          ⁵School of Chemistry, University of New South Wales, Sydney, NSW 2052, Australia

ABSTRACT: Despite the advances in host-guest chemistry, macrocyclic hosts with deep cavities are far from abundant among the large number of wholly synthetic hosts described in the literature. Herein, we describe the design and synthesis of two new tubular hosts—namely, corral[4]arene and corral[5]arene. The former has been isolated and characterized as two conformational diastereoisomers—one is centrosymmetric and the other is asymmetric. The latter—a five fold symmetrical and flexible host—has also been investigated in detail. It is composed of five 4,4′-dimethoxybiphenyl units bridged by ethynylene linkers at their 2,2′-positions and adopts a pentagonal conformation with a tubular-shaped cavity in the presence of guests. This structure endows corral[5]arene, not only with a conjugated backbone, capable of bright fluorescent emission (quantum yield, 56%), but also a deep π-electron-rich aromatic cavity with remarkable conformational flexibility. The adaptive cavity of corral[5]arene allows it to accommodate a wide range of neutral and positively charged electron-deficient guests with different molecular sizes and shapes. Binding constants between this host and these guests in three different non-polar organic solvents lie in the range of 10³ to 10⁷ M⁻¹. Moreover, corral[5]arene exhibits dynamic chirality on account of the axes of chirality associated with each of the five biphenyl units and displays first-order transformation as exhibited by circular dichroism in response to the addition of chiral guests. All these stereochemical features render corral[5]arene an attractive host for a variety of supramolecular and nanotechnological applications