Multi-Stimuli-Responsive Directional Assembly of an Amphiphilic Donor-Acceptor Alternating Supramolecular Copolymer

Abstract

The stimuli-responsive supramolecular co-assembly of two π-amphiphiles, NDI-1 and Py-1, in which an acceptor (A) (naphthalene diimide) and a donor (D) (pyrene) chromophore, respectively, serve as the hydrophobic segment, is described. In addition, both contain an amide group in a designated location so that H-bonding and D–A charge-transfer (CT) interactions can operate simultaneously. H-bonding among the amide groups not only enhanced the CT interaction promoted by the alternating D–A stacking propensity, but also fixed the lateral orientation of the two chromophores and thus compelled the anionic and nonionic hydrophilic head groups, appended with the D and A amphiphiles, respectively, to remain segregated on two opposite sides of the amphiphilic alternating supramolecular copolymer. This copolymer showed spontaneous polymersome assembly with the D-appended anionic groups displayed at the outer surface, whereas the A-appended hydrophilic wedge converged at the inner lacuna. In contrast, spherical or cylindrical micellar structures were produced by Py-1 and NDI-1, respectively. Effective functional-group display in the D–A supramolecular polymersome enabled protein-surface recognition and inhibition of the enzymatic activity of Cht. Under a reducing environment, formation of NDI.− jeopardized the D–A interaction and thus the A chromophores were ejected out of the membrane of the polymersome causing its gradual contraction in size by >75 %. D–A supramolecular polymersomes also exhibited a lower critical solution temperature that could be tuned across a temperature window of 40 to 70 °C by varying the ratio of the A and D components in the alternating supramolecular copolymer.