title: Quadruple switching of pleated foldamers of tetrathiafulvalene-bipyridinium alternating dynamic covalent polymers.
abstract: Two dynamic covalent polymers P1 and P2 were prepared by alternately linking electron-rich tetrathiafulvalene (TTF) and electron-deficient bipyridinium (BIPY(2+) ) 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 BIPY(2+) 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) (CBPQT(2(.+)) ) 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 BIPY(2+) , the first folded state was regenerated. Switching or conversion between the four conformational states was confirmed by UV/Vis spectroscopic experiments.
authors: Department of Chemistry, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Fudan University, 220 Handan Road, Shanghai 200433 (China).
authors: Lan
authors: L
authors: Chen
authors: Hui
authors: H
authors: Wang
authors: Dan-Wei
authors: DW
authors: Zhang
authors: Yaming
authors: Y
authors: Zhou
authors: Zhan-Ting
authors: ZT
authors: Li
keywords: donor-acceptor interactions; dynamic covalent polymers; foldamers; radical cations; viologens