Light-induced ostwald ripening of organic nanodots to rods

Ostwald ripening allows the synthesis of 1D nanorods of metal and semiconductor nanoparticles. However, this phenomenon is unsuccessful with organic π-systems due to their spontaneous self-assembly to elongated fibers or tapes. Here we demonstrate the uses of light as a versatile tool to control the ripening of amorphous organic nanodots (ca. 15 nm) of an azobenzene-derived molecular assembly to micrometer-sized supramolecular rods. A surface-confined dipole variation associated with a low-yield (13–14%) trans–cis isomerization of the azobenzene moiety and the consequent dipole–dipole interaction in a nonpolar solvent is believed to be the driving force for the ripening of the nanodots to rods

Evolution of nano- to microsized spherical assemblies of a short oligo(p-phenyleneethynylene) into superstructured organogels

Wires to particles: A subtle balance of H-bonding, π-stacking, and van der waals interactions facilitates the concentration-controlled self-assembly of a short molecular wire (see figure) into nanoparticles and fluorescent microspheres in nonpolar hydrocarbon solvents. Above a critical concentration, a blue-light emitting organogel is formed

Role of complementary H-bonding interaction of a cyanurate in the self-assembly and gelation of melamine linked tri(p-phenyleneethynylene)s

Melamine-functionalized tri(p-phenyleneethynylene) 1 self-assembles to form opaque and weak gels in aliphatic solvents which turned transparent and stable upon addition of a cyanurate, affording supramolecular nanostructures with distinct physical properties

Reversible self-assembly of entrapped fluorescent gelators in polymerized styrene gel matrix: erasable thermal imaging via recreation of supramolecular architectures

The reversible shift of emission in fluorescent molecular gelators has been explored for the preparation of a composite polymer film useful for erasable thermal imaging and secret documentation. A gelation-assisted photopolymerization of styrene allowed the entrapment of the fluorescent gelator molecules within a polystyrene matrix with a weak green fluorescence, which upon heating above the Tg of the polymer resulted in high-contrast fluorescence images due to the strong blue fluorescence of the individual molecules. The blue emission from the disassembled oligo(p-phenylenevinylene) molecules (OPVs) could be reversed to the green emission of the self-assembled OPVs by exposing the polymer film to chloroform vapors. The thermally written images are visible only under UV light and cannot be photocopied. A solvent-vapor-controlled recreation of the self-assembly of a fluorescent organogelator within a polymer matrix and its application in erasable secret documentation has not been reported previously

From vesicles to helical nanotubes: a sergeant-and-soldiers effect in the self-assembly of oligo(p-phenyleneethynylene)s

Coassembly of short molecular wires OPE1 with chiral analogues OPE2, both of which are CD silent, exhibited a sergeant-and-soldiers effect that resulted in transformation of vesicular aggregates of OPE1 into CD-active helical nanotubes (see schematic picture), as revealed by CD, dynamic light scattering, and atomic force and transmission electron microscopies (TEM). OPE=oligo(p-phenyleneethynylene)

Solvent-directed self-assembly of π gelators to hierarchical macroporous structures and aligned fiber bundles

Morphology variation: The Boc-alanine linked OPV exhibits an unprecedented formation of periodic macroporous honeycomb structures in chloroform and aligned fiber bundles in toluene (see SEM images). This represents a unique example for a distinct morphology change of an organogelator from macroporous honeycomb to aligned fiber bundles upon changing the solvent

Light-Induced Ostwald Ripening of Organic Nanodots to Rods

Ostwald ripening allows the synthesis of 1D nanorods of metal and semiconductor nanoparticles. However, this phenomenon is unsuccessful with organic π-systems due to their spontaneous self-assembly to elongated fibers or tapes. Here we demonstrate the uses of light as a versatile tool to control the ripening of amorphous organic nanodots (ca. 15 nm) of an azobenzene-derived molecular assembly to micrometer-sized supramolecular rods. A surface-confined dipole variation associated with a low-yield (13–14%) <i>trans–cis</i> isomerization of the azobenzene moiety and the consequent dipole–dipole interaction in a nonpolar solvent is believed to be the driving force for the ripening of the nanodots to rods

Toroidal nanoobjects from rosette assemblies of melamine-linked oligo(p-phenyleneethynylene)s and cyanurates

Nanodonuts: A hydrogen-bonded cyclic assembly (rosette, left) of a melamine featuring π-conjugated oligo(p-phenyleneethynylene) hierarchically self-organizes with a cyanurate in decane under dilute conditions to form toroidal nanostructures (right) with a diameter of 40 nm

Sustainable Electronic Materials: Reversible Phototuning of Conductance in a Noncovalent Assembly of MWCNT and Bioresource-Derived Photochromic Molecule

Tuning the microstructure, conductance, band gap of a single molecule with an external stimuli such as light have vital importance in nanoscale molecular electronics. Azobenzene systems are inimitable light responsive molecules suitable for the development of optically modulated materials. In this work we have demonstrated the development of an optically active Multiwalled Carbon Nanotube (MWCNT)-hybrid material by the noncovalent functionalization of azo based chromophore derived from cardanol, a bioresource material. This photoresponsive noncovalent hybrid shows trans–cis photoisomerization induced switching of conductance. We report this as the first example in which the photochromic assembly developed from a bioresource material exhibited tunable conductivity. We expect that this novel photoswitchable hybrid with reversible conductance may have potential applications in nanoscale molecular electronics, solar cells, OLEDs, etc

Rational design of nanofibers and nanorings through complementary hydrogen-bonding interactions of functional π systems

A simple protocol to create nanofibers and -rings through a rational self-assembly approach is described. Whereas the melamine-oligo(p-phenylenevinylene) conjugate 1 a self-aggregates to form ill-defined nanostructures, conjugate 1 b, which possesses an amide group as an additional interactive site, self-aggregates to form 1D nanofibers that induce gelation of the solvent. AFM and XRD studies have shown that dimerization through the melamine-melamine hydrogen-bonding interaction occurs only for 1 b. Upon complexation with 1/3 equivalents of cyanuric acid (CA), conjugate 1 a provides well-defined, ring-shaped nanostructures at micromolar concentrations, which open to form fibrous assemblies at submillimolar concentrations and organogels in the millimolar concentration range. Apparently, the enhanced aggregation ability of 1 a by CA is a consequence of columnar organization of the resulting discotic complex 1 a<SUB>3</SUB>CA. In contrast, coaggregation of 1 b with CA does not provide well-defined nanostructures, probably due to the interference of complementary hydrogen-bonding interactions by the amide group