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

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.