Quadruple Switching of Pleated Foldamers of Tetrathiafulvalene-Bipyridinium Alternating Dynamic Covalent Polymers

• Published in: Angewandte Chemie International Edition Vol. 54; no. 13; pp. 4028 - 4031
• Main Authors: Chen, Lan, Wang, Hui, Zhang, Dan-Wei, Zhou, Yaming, Li, Zhan-Ting
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 23.03.2015; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: Acetonitrile; Conversion; Covalence; Dimerization; donor-acceptor interactions; dynamic covalent polymers; Dynamics; foldamers; Oxidation; Polymers; Protein folding; radical cations; Radicals; Switching; viologens; viologens; radical cations; donor-acceptor interactions; dynamic covalent polymers; foldamers
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201410757

Two dynamic covalent polymers P1 and P2 were prepared by alternately linking electron‐rich tetrathiafulvalene (TTF) and electron‐deficient bipyridinium (BIPY2+) through hydrazone bonds. In acetonitrile, the polymers were induced by intramolecular donor–acceptor interactions to form pleated foldamers, which unfolded upon oxidation of the TTF units to the radical cation TTF.+. Reduction of the BIPY2+ units to BIPY.+ led to the formation of another kind of pleated secondary structures, which are stabilized by intramolecular dimerization of the BIPY.+ units. The diradical dicationic cyclophane cyclobis(paraquat‐p‐phenylene) (CBPQT2(.+)) could further force the folded structures to unfold by including the BIPY.+ units of the polymers. Upon oxidation of the BIPY.+ units of the cyclophane and polymers to BIPY2+, the first folded state was regenerated. Switching or conversion between the four conformational states was confirmed by UV/Vis spectroscopic experiments. Dancing to four different tunes: Tetrathiafulvalene and bipyridinium can be oxidized and reduced, respectively, to radical cations. Depending on their redox state, a donor–acceptor interaction or a radical‐cation dimerization can occur. These noncovalent forces have been used to induce two tetrathiafulvalene–bipyridinium alternating dynamic covalent polymers to fold (see picture) and unfold reversibly in four ways.