Reversible Control of Radius and Morphology of Fluorene-Azobenzene Copolymer Nanowires by Light Exposure

The preparation of photoresponsive polymer nanowires comprising photochromic azobenzene (Azo) and p-conjugated fluorene (FO) units is reported. Well-defined and uniform nanowires of the copolymer (PFOAzo) were successfully fabricated by the single particle nanofabrication technique after optimizing the FO: Azo ratio and the development conditions. Azo units in the PFOAzo nanowires underwent reversible trans-cis-trans isomerization upon exposure to ultraviolet or visible light, leading to changes in the radius (between ca. 6 and 8 nm) and morphology (straight or wavy) of the nanowires. The oligo(alkylfluorene) units in the backbone are found to profit the crosslinking efficiency upon high-energy ion beam irradiation, and more importantly, provide sufficient flexibility to allow reversible photoswitching. This demonstration of the photoluminescence, semiconducting, and mechanical properties of the PFOAzo nanowires is an important advance in the evolution of electro-mechanical nanomaterials.