Wrapping of Self-Organized Fluorescent Nanofibers with a Silica Wall

Abstract

Amphiphilic compounds 1 and 2, composed of an aromatic pyrene core and an amphiphilic three-branched unit, were synthesized and investigated for their self-organizing process in solution by UV-vis, fluorescence spectra, Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and fluorescence microscopes. While 2 formed spherical objects in a mixed solvent of methanol and water, 1 assembled into long, flexible, and fluorescent fibers through pi-pi stacking of pyrene cores and hydrogen bonding among amide groups. The fluorescence spectra and morphologies strongly depended on the concentration and solution temperature. The fibrous assemblies were wrapped with an ultrathin silica wall by the acidic sol-gel polymerization of tetraethoxysilane (TEOS). A transmission electron microscopy (TEM) image after the sol-gel polymerization showed discrete fibrous structures with a uniform diameter of 3.5 nm and several micrometers in length. The thickness of the silica wall and the inner diameter of one fiber were estimated to be 0.5 nm and 2.5 nm, respectively. The observed inner diameter of the fiber was almost compatible with the width of the cylindrical assembly made of 1. The pyrene unit in 1 can interact with the sidewall of single-walled carbon nanotubes (SWNTs) through pi-pi interaction, and the adsorption of 1 onto the surface of SWNTs could disrupt the formation of bundles. The accumulation of oligomeric silica species at the hydrophilic surface created organic-inorganic nanoscopic fibers containing electronic conductive SWNTs.

Pyrene-functionalized organogel and spacer effect: from emissive nanofiber to nanotube and inversion of supramolecular chirality

“…It has been reported that the pyrene excimer emission band depends on the conformation of the excimer: the sandwich type excimer shows an emission band at 460 nm, and the band at 416 nm is ascribed to the partial overlap type excimer. [37][38][39][40] Here, the pyrene moiety in the PyC0 gels formed an excimer with a partial overlap as a result of pyrene being linked to glutamide directly. In the self-assemblies of the gels, an intermolecular hydrogen-bonding array of the glutamide moieties disturbed the formation of excimer structures.…”

Organic Fluorescent Nanofibers and Sub-Micrometer Rods

“…4). Amphiphilic compounds that self-organize into fluorescent nanofibers can be obtained by branching, for example, three poly(ether) segments to a pyrene core (12) (Kimura et al, 2009). In the T-shaped aromatic amphiphiles based on oligo(ethylene oxide) dendrons (13), the aromatic segments are stacked with dimeric association to maximize π−π interactions.…”

“…It is noteworthy that the fibers made of 12 were subsequently wrapped with an ultrathin silica wall, using a sol-gel process. The resulting fibers can then be considered as electronic cables that are composed of a conductive organic core and an insulating inorganic layer (Kimura et al, 2009). …”

Fabrication of organogels composed from carbon nanotubes through a supramolecular approach

“…25,26 For example, Chen et al 26 have obtained the organogels of SWNTs with ferrocene-grafted poly (p-phenyleneethynylene)s through non-covalent interactions. Considering pyrene is the most popular species for non-covalent attachment with CNT through p-p stacking, [27][28][29] in this paper, we designed a new low molecular gelator bearing a pyrene group and fabricated organogels with pristine SWNTs through mixing with LPG.…”