Positional Isomers of Chromophore–Peptide Conjugates Self‐Assemble into Different Morphologies

Abstract

Ordering π-systems into defined supramolecular structures is important for the development of organic functional materials. In recent years, peptides with defined secondary structures and/or self-assembly properties were introduced as powerful tools to order peptide-chromophore conjugates into different morphologies. This work explores whether or not the directionality of peptides can be used to control the self-assembly. The position of the π-system in conjugates between oligoprolines and perylene monoimide (PMI) chromophores was varied by attaching the PMI moiety to the second-to-last residue from the C- and N-termini, respectively. Microscopic and diffraction analysis revealed that the positional isomers form distinctly different supramolecular architectures that extend into the micrometer regime. NMR spectroscopic studies in solution phase allowed correlation of the self-assembly properties with markedly different conformational preferences of the isomeric building blocks. These insights enabled the design of building blocks with predictable self-assembly properties. Thus, the directionality of peptides offers exciting opportunities for controlling the self-assembly and electronic properties of π-systems.

Oligoprolines guide the self-assembly of quaterthiophenes

“…Thus, the results provide guidelines for the rational design of related conjugates with predictable self-assembly properties. In addition, prior studies with oligoproline–perylene monoimide conjugates had provided supramolecular assemblies with unique molecular arrangements 21–23. The present study thus suggests to target triades comprising perylene chromophores, oligothiophenes, and the oligoproline scaffold as this design creates a combination of electron-donor and electron-acceptor components.…”

“…Thus, within these conjugates the quaterthiophene is located at the same position with only the length of the oligoproline changing. The second proline residue was chosen as an anchoring site since this conjugation site had resulted in highly ordered assemblies with PMI–oligoproline conjugates 23. For the sake of comparison with these oligomers, we also linked the quaterthiophene to a monomeric azidoproline (Azp) residue to form conjugate 1 (Fig.…”

“…We have previously shown that a minimalistic (A–B) design based on conjugates of a single proline residue and a quaterthiophene moiety results in chiral, micellar assemblies 19,20. We have also demonstrated that oligoproline scaffolds can guide the hierarchical self-assembly of sterically demanding electron-poor perylene monoimide (PMI) chromophores into a variety of unprecedented nanostructures 21–23. Oligoprolines adopt the left-handed PP II helix in which every third residue is stacked on top of each other at a distance of 9 Å (Fig.…”

“…Also in contrast to other peptides, short oligoprolines do not aggregate with each other and have therefore been used as inert molecular rulers and scaffolds 28,29. The studies on oligoproline–PMI conjugates furnished a remarkable outcome: two moieties that do not assemble on their own can, once conjugated, self-assemble into complex nanostructures 21–23. The question now arises whether oligoprolines can also control the self-assembly of electron-rich oligothiophenes, which have a pronounced intrinsic tendency toward π–π stacking 6…”

Peptide–Protein Interactions: From Drug Design to Supramolecular Biomaterials

“…Interestingly, supramolecular assemblies, including nanostructured sheets, curls, or ribbons with variable length of the oligoproline moiety, could shape the assembly of the quaterthiophenes into parallel or antiparallel π-π stacked aggregates and could affect the molecular organization of the conjugates from monolayers to double- layered sheets and helically twisted ribbons. As the performance of organic electronic devices depends on their molecular organization in the solid state [ 191 , 192 ], the study provided guidelines for the rational design of related conjugates with predictable self-assembly properties and a combination of electron-donor and electron-acceptor components for supramolecular assemblies with unique molecular arrangements [ 186 , 187 , 188 , 193 ].…”