Light-Induced Contraction and Extension of Single Macromolecules on a Modified Graphite Surface

Abstract

Synthetic rigid-rod polymers incorporating multiple azobenzene photoswitches in the backbone were deposited from solution onto a monolayer of octadecylamine covering the basal plane of graphite. Large contractions and extensions of the single macromolecules on the surface were induced by irradiation with UV and visible light, respectively, as visualized by scanning force microscopy. Upon contraction, the single polymer chains form more compact nanostructures and also may move across the surface, resembling a crawling movement. We attribute the efficiency of these processes to the low mechanical and electronic coupling between the surface and polymers, the high density of azobenzenes in their backbones, and their rigidity, allowing for maximized photodeformations. The visualization of on-surface motions of single macromolecules directly induced by light, as reported herein, could help promote the development of optomechanical nanosystems.

Shape‐Shifting Azo Dye Polymers: Towards Sunlight‐Driven Molecular Devices

“…The synthesis of rigid‐rod azobenzene‐containing poly( para‐ phenylene) backbones is one strategy to maximize photo‐deformation, enabling accordion‐like compression and extension of chains upon cycling with UV and visible light ( Figure a) . Lee et al demonstrated that these single‐chain polymeric assemblies may even exhibit crawling movements when deposited onto a graphite surface modified with octadecylamine, and imaged with scanning force microscopy (Figure b) . Chemically or physically cross‐linked supramolecular assemblies of these linear photo‐mechanical polymers may be envisioned to lift weights, behave as actuators, and to perform other types of directed work with greater resistance against deformation fatigue than individual strands .…”

“…The functionalization or tethering of the polymer strands to scaffolds may enable the macromolecules to perform work by lifting weights or transporting cargo. Reproduced with permission . Copyright 2014, American Chemical Society.…”

“…[108] Lee et al demonstrated that these singlechain polymeric assemblies may even exhibit crawling movements when deposited onto a graphite surface modified with octadecylamine, and imaged with scanning force microscopy (Figure 7b). [109] Chemically or physically cross-linked supramolecular assemblies of these linear photo-mechanical polymers may be envisioned to lift weights, behave as actuators, and to perform other types of directed work with greater resistance against deformation fatigue than individual strands. [110] Fang et al, for example, reported using a simple method of melt spinning to fabricate azobenzene-containing main chain polymers hydrogen-bonded into cross-linked fibers (Figure 8).…”

“…Reproduced with permission. [109] Copyright 2014, American Chemical Society. the pulleys to 'pull' and 'push', the belt was driven continuously in counter-clockwise rotational motion when the light was on (Figure 9a).…”

Orchestrating Molecular Motion with Light – From Single (macro)Molecules to Materials

“…We have highlighted earlier the exciting opportunities associated with the on-command reversible binding of biological ligands to [ 41 ] Copyright 2014, American Chemical Society.…”