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Nanowires occupy a prestigious place in nanoelectronics, nanomechanics, and biomimetics. Although there are notable methods to grow nanowires via self-assembly, there is a key drawback in the need to find out the specific conditions appropriate for each system. In this sense, universal techniques to fabricate such nanowires from various organic materials have been sought for the continued progress of the related research field. Here we report one of the promising and facile methodologies to quantitatively produce nanowires with controlled geometrical parameters. In this method, referred to as “Single Particle-Triggered Linear Polymerization (STLiP)”, organic thin films on a supporting substrate were irradiated with high-energy charged particles, accelerated by particle accelerators. Each particle penetrates from the top of the films to the substrate while gradually releasing kinetic energy along its trajectory (ion track), generating reactive intermediates such as radical species that eventually induce propagation reactions. The resulting polymerized products were integrated into nanowires with uniform diameter and length that can be isolated via development with appropriate organic solvents. Considering the widely applicable nature of STLiP to organic materials, the present technique opens a new door for access to a number of functional nanowires and their assembly.

Highly fluorescent nanowires were produced quantitatively by one-for-one reactions between a high energy charged particle and fluorescent organic molecules via efficient solid-state polymerization reactions. The initiation and propagation reactions take place non-homogeneously along the trajectories of the particles within nm-sized cylindrical area, thus giving uniform nanowires with controlled sizes after isolation by removing non-irradiated (unreacted) molecules by organic solvents. Highly emissive properties of the nanowires even after isolation were clearly observed similar to their initial films, indicating that the polymerization process might not spoil the efficient fluorescent framework of the compound: excited state intra-molecular proton transfer (ESIPT) process. We also demonstrated that the fluorescent nanowires have potential of sensing the trace amount of nitrobenzene that was monitored by fluorescence spectroscopy.

“Clickable” nanowires with well-defined and uniform structures made of conjugated polyfluorene polymers were successfully fabricated by single particle nanofabrication technique (SPNT). Poly[(9,9-dihex-5-yn-1-ylfluorenyl-2,7-diyl)-co-(9,9′-di-noctylfluorenyl- 2,7-diyl)] (F6E8) and poly[(9,9-dihex-5-yn-1-ylfluorenyl- 2,7-diyl)-co-(2,2′-bithiophene)] (F6E2T) underwent an efficient cross-linking reaction upon irradiation, resulting in formation of one-dimensional nanostructures with high and desired aspect ratio reaching up to 200. Alkyne groups on the surface of nanowires were functionalized effectively by click reaction with fluorescent 5- TAMRA-PEG3-azide, which was confirmed by confocal microscopy. Substrates functionalized with the nanowires provide dramatic expansion of “clickable” surface area immobilized directly with TAMRA, and the fluorescence resonance energy transfer (FRET) processes between TAMRA and nanowire backbones are demonstrated as biological sensing platforms.