Light-Gated Nano-Porous Capsules from Stereoisomer-Directed Self-Assemblies

Structuring pores into stable membrane and controlling their opening is extremely useful for applications that require nanopores as channels for material exchange and transportation. In this work, nanoporous vesicles with aggregation-induced emission (AIE) properties were developed from the amphiphilic polymer PEG550-TPE-Chol, in which the hydrophobic part is composed of a tetraphenylethene (TPE) group and a cholesterol moiety and the hydrophilic block is a poly(ethylene glycol) (PEG, M_n = 550 Da). Two stereoisomers, trans-PEG550-TPE-Chol and cis-PEG550-TPE-Chol, were successfully synthesized. These thermally stable stereoisomers showed distinct self-assembly behavior in water: trans-PEG550-TPE-Chol formed classical vesicles, while cis-PEG550-TPE-Chol self-assembled into cylindrical micelles. Interestingly, trans/cis mixtures of PEG550-TPE-Chol (trans/cis = 60/40), either naturally synthesized without isomers' separation during the synthesis or intentionally mixed using trans- and cis-isomers, constructed perforated vesicles with nanopores. Moreover, under the illumination of high intensity UV light (365 nm, 15 mW/cm²), the classical vesicles of trans-PEG550-TPE-Chol were perforated by its cis counterparts generated from the trans-cis photoisomerization, while the cylindrical micelles of cis-PEG550-TPE-Chol interweaved to form meshes and nanoporous membranes due to the trans-isomers produced by cis-trans photoisomerization. All of these assemblies in water emitted bright cyan fluorescence under UV light, while their constituent molecules were not fluorescent when solubilized in organic solvent. The AIE fluorescent normal vesicles and nanoporous vesicles may find potential applications in biotechnology as light-gated delivery vehicles and capsules with nanochannels for material exchange.