Protonation-induced switching of pleated foldamers of diaminonaphthalene-bipyridinium polymers

1,5-diaminonaphthalene (DAN) and bipyridinium (BIPY²⁺) were copolymerized into NP1 and NP2 linked by acylhydrazone bonds. The formed intramolecular charge-transfer (CT) complex drove the linear foldamers to adopt pleated folding conformation. Upon protonation of the DAN units by triflic acid (TFSA), the pleated folding conformation unfolded to linear structure because of electron repulsion. And this linear structure can be refolded to pleated structure by titrating with triethylamine (TEA). 1,5-dinaphtho38]crown-10 (DN38C10) can encapsulate bipyridinium group on the polymers after protonation. These processes were supported by UV–vis and fluorescence spectroscopy studies.