2D Assemblies Based on a Tetraphenylethylene D,L-Cyclic Peptide Scaffold

Abstract

Two dimensional (2D) materials and aggregation-induced emission (AIE) fluorophores have recently gained attention due to their unique properties and application potential. However, the combination of AIE probes into 2D self-assembled systems under nanometric control remains elusive due to the sensitivity of supramolecular assemblies to subtle changes in the monomer structure. Herein, we present a new scaffold based on four nanotube-forming cyclic peptide (CP) units attached to a tetraphenylethene (TPE) core whose pH-dependent self-assembly results in light-emitting 2D nanosheets. An oxime bond connection was exploited to synthesize a discrete library of tetrakis-(cyclopeptide) tetraphenylethene monomers that self-assemble into 2D macrotubular nanoarrays under the suitable external stimulus. This new tetrameric CP motif tolerates a broad range of molecular modifications, both on the peptide backbone and TPE core, without compromising the integrity of the 2D self-assembly. We also discovered that adjusting the molecular structure of the TPE aromatic core enabled precise height control of the supramolecular nanosheets. The alignment of the histidine residues within neighboring CPs allowed the application of 2D nanoarchitectures as enzyme mimics with esterase activity. The excellent tolerance to molecular diversity in both the external CP moiety and the internal aromatic AIE core, invites the design of new functional 2D supramolecular materials.