Color-Tuned Highly Fluorescent Organic Nanowires/Nanofabrics: Easy Massive Fabrication and Molecular Structural Origin

Abstract

The development of one-dimensional fluorescent nanowires (1D-NWs) and their higher-dimensional architectures such as nanowebs and nanofabrics (2D-NFs) could open a new area in nanomaterials science and nanotechnology. In particular, fluorescent pi-electronic 1D-NWs are considered promising materials for realizing innovative nanodevices together with semiconductors and metallic NWs. We earlier reported that 1-cyano-trans-1,2-bis-(3',5'-bis-trifluoromethyl-biphenyl)ethylene (CN-TFMBE), a simple but very peculiar derivative of oligo(p-phenylene vinylene)s (OPV) composed of a cyano-stilbene backbone, self-assembles easily into 1D-NWs with highly enhanced fluorescence emission in the solid state. We report herein surprising new outcomes obtained from a more detailed exploration of the self-association behavior of CN-TFMBE and its analogues. We found that CN-TFMBE self-assembled into highly fluorescent 1D-NWs and 2-D NFs very easily and massively, irrespective of whether drop casting, spin coating, or vacuum deposition was used for processing. However, we additionally found that, if the backbone cyano group or trifluoromethyl substituents were removed from CN-TFMBE, the resulting molecule did not form 1D-NWs under any conditions. Through structural analyses using mid- and wide-angle X-ray diffraction methods and multiscale computer simulation techniques, we formulated molecular structural guidelines for programming pi-electron molecules into highly fluorescent 1D-NWs and 2-D NFs. Interestingly, we demonstrated that R,G,B,Y-color tuned 1D-NWs and NFs could be easily and massively fabricated based on our guidelines. This class of highly fluorescent color-tuned organic pi-electronic nanomaterial is expected to open a new phase in applications such as nanoscale optoelectronics, sensing, and biological devices.