Nanostructures composed of conjugated polymers or π-conjugated molecules provide sensing platforms with large specific surface areas. One of the feasible approaches to accessing such nanostructured miniaturized sensors with ultrahigh sensitivity is to develop a network of organic nanowires with optical/electronic properties that can measure signals upon interacting with the analytes at their surfaces. In this work, organic nanowires with controlled number density and uniform length were fabricated by one-dimensional solid-state polymerization of 9,9'-spirobi[9 H-fluorene] (SBF) derivatives triggered by high-energy single particles. SBF was chosen as a conjugated molecular motif with the interplay of high density of π-electrons, high solubility, and uniform solid-state structures, allowing us to fabricate sensing platforms via solution processing. The as-deposited energy density in linear polymerization nanospace was theoretically analyzed by a collision model, interpreting nanowire sizes at subnanometer levels. The substitution of bromine atoms was confirmed to be effective not only for the higher collision probability of the incident particles but also for the remarkable increase in radiolytic neutral radical yield via C-Br cleavages or electron-dissociative attachments onto the bromine atoms. The fluorescence spectra of SBF-based nanowires were different from those of SBF derivatives due to extended bond formation as a result of polymerization reactions. Fluorescence was quenched by the addition of nitrobenzene, indicating the potential use of our nanowires for fluorometric sensing applications. Microwave-based conductivity measurements revealed that the SBF-based nanowires exhibited charge carrier transport property upon photoexcitation, and that the conductivity was changed upon treatment with nitrobenzene vapors. The presented strategy of bromination of aromatic rings for efficient fabrication of controlled nanowire networks with favorable fluorescent and charge transport properties of nanowires advances the development of nanostructured sensing systems.

Construction of large-area electron donor–acceptor (D–A) interfaces and hole/electron pathways is important for photoconducting and photovoltaic functions. Although blends of D- and A-type discotic π-systems have a possibility to realize one-dimensional charge carrier pathways as well as heterointerfaces, D–A segregated structures are difficult to develop by self-assembly because they are entropically unfavored structures. Here we report the use of shish-kebab-type hole-transporting discotic columns fixed by a self-threading polysiloxane chain and approach to such segregated nanostructures. Electron-donor/acceptor blends of soluble phthalocyaninato­polysiloxanes (Poly-SiPcs) and perylenedicarboximides (PDIs) were prepared, and their photoconductive property was investigated. Although Poly-SiPc1 shows a photoinduced charge separation with PDI1 analogous to the corresponding monomeric phthalocyanines (SiPc1 and H 2 Pc1), the Poly-SiPc1/PDI1 system displays a remarkably larger photoconductivity than SiPc1/PDI1 and H 2 Pc1/PDI1, which mostly results from the presence of hole-transporting pathways with the mobility μh,1D ∼ 0.1 cm2 V–1 s–1 in Poly-SiPc1 along the polysiloxane covalent bonds even upon mixing with PDI1. When π-stackable PDI2 is used instead of PDI1, X-ray diffraction analysis disclosed obvious signs of π-stacking periodicities for both Pc and PDI planes in the mixture, indicating the presence of donor–acceptor segregated domains of columnar structures. As a result, photoexcitation of Poly-SiPc1/PDI2 generates highly mobile holes and electrons, leading to the observation of a much larger conductivity.

Energy released from an accelerated high-energy single/cluster particle triggers solid-state polymerization and cross-linking reactions of porphyrin-based π-conjugated monomers within a nanometer-scaled one-dimensional spatial area along the ion trajectory, resulting in the formation of an insoluble nanowire with a precise diameter and length. The nanowires are isolated by the development processimmersion of the irradiated film in organic solventsand their shape and geometry are clearly characterized by atomic force microscopy. The obtained nanowire bundles, reflecting precisely the number of incident particles, show characteristic absorption spectra originating from porphyrin chromophores without significant degradation of the molecular cores. These porphyrin-based nanowires can be further functionalized into metallocomplexes by immersing the nanowires into solutions containing metal ion sources. The remarkable finding on the monomer structural parameters is that terminal alkyne groups are preferentially reacted and thus highly effective as a monomer structure for the present single particle-triggered linear polymerization method. The porphyrin-based nanowires show much higher photoconductivity than the precursor porphyrin films and enhanced fluorescence on silver nanoparticle layers via surface plasmon resonance. The porphyrin nanowires serve as photosensitizers mediating the generation of singlet oxygens, which is attractive for the use as a controlled nanosystem toward photocatalysis and photodynamic therapy.

A particle induces a pack of chemical reactions in nanospace: chemical reactions confined into extremely small space provide an ultimate technique for the nanofabrication of organic matter with a variety of functions. Since the discovery of particle accelerators, an extremely high energy density can be deposited, even by a single isolated particle with MeV-ordered kinetic energy. However, this was considered to cause severe damages to organic molecules due to its relatively small bond energies, and lack of ability to control the reactions precisely to form the structures while retaining physico-chemical molecular functionalities. Practically, the severely damaged area along a particle trajectory: a core of a particle track has been simply visualized for the detection/dosimetry of an incident particle to the matters, or been removed to lead nanopores and functionalized by refilling/grafting of fresh organic/inorganic materials. The use of intra-track reactions in the so-called “penumbra” or “halo” area of functional organic materials has been realized and provided us with novel and facile protocols to provide low dimensional nano-materials with perfect size controllability in the 21st century. These protocols are now referred to as single particle nanofabrication technique (SPNT) and/or single particle triggered linear polymerization technique (STLiP), paving the way towards a new approach for nanomaterials with desired functionalities from original molecules. Herein, we report on the extremely wide applicability of SPNT/STLiP protocols for the future development of materials for opto-electronic, catalytic, and biological applications among others.

The critical dimension of semiconductor devices is approaching the single-nm regime, and a variety of practical devices of this scale are targeted for production. Planar structures of nano-devices are still the center of fabrication techniques, which limit further integration of devices into a chip. Extension into 3D space is a promising strategy for future; however, the surface interaction in 3D nanospace make it hard to integrate nanostructures with ultrahigh aspect ratios. Here we report a unique technique using high-energy charged particles to produce free-standing 1D organic nanostructures with high aspect ratios over 100 and controlled number density. Along the straight trajectory of particles penetrating the films of various sublimable organic molecules, 1D nanowires were formed with approximately 10~15 nm thickness and controlled length. An all-dry process was developed to isolate the nanowires, and planar or coaxial heterojunction structures were built into the nanowires. Electrical and structural functions of the developed standing nanowire arrays were investigated, demonstrating the potential of the present ultrathin organic nanowire systems.