On the transfer of cooperative self-assembled π-conjugated fibrils to a gold substrate.

The transfer of the cooperative self-assembled fibrils to a gold substrate has been studied by means of scanning probe microscopy techniques revealing the crucial role of the early formation of a monolayer.

Atomic force microscopy nanomanipulation of shape persistent, spherical, self-assembled aggregates of gold nanoparticles.

Gold (Au) nanoparticles have been synthesized that are stabilized by an organic ligand bearing a dithiolane functional group for binding to Au, an oligo(p-phenylene vinylene) (OPV) chromophoric group to drive self-assembly via π-π interactions, and a hydroxy functionality for interparticle hydrogen bonding. The OPV-Au particles reversibly self-assemble in n-heptane solution, forming shape persistent, spherical, nanometer-sized aggregates that do not collapse on a substrate. Optical absorption and transmission electron microscopy tomography studies show that the size and shape persistency can be tuned by modification of the ligands, adjustment of the core size, and variation of the concentration. The spherical assemblies can be manipulated with the tip of an atomic force microscope: an aggregate can be pushed over the surface for at least 20 times with nanometer precision and without substantial loss of material.

Disk micelles from amphiphilic Janus gold nanoparticles.

Janus gold nanoparticles are synthesised via a simple preparation method and behave as amphiphiles self-assembling in water into disk-shaped micelles.

The influence of hydrogen bonding and pi-pi stacking interactions on the self-assembly properties of C3-symmetrical oligo(p-phenylenevinylene) discs.

Three C3-symmetrical discotics containing a 1,3,5-benzenetricarboxamide unit functionalized with pi-conjugated oligo(p-phenylenevinylene)s (OPV)s have been synthesized and fully characterized. For the two amide OPV discs a two-step transition from helical stacks to molecularly dissolved species was observed and surprisingly, the topology of the amide determines the stability and helicity of the fibers in solution and the length of the fibrils at a surface. In case of the bipyridine disc, aggregates were formed that show little chiral ordering while the stacks remain present over a large temperature range. At a surface, completely disordered structures exist probably as a result of competing types of pi-pi stacking interactions that differ in strength and orientation. The results show that the design of functional self-assembled architectures based on hydrogen bonding and pi-pi stacking interactions is an extremely delicate matter and reveal that special demands have to be taken into account to balance the topology, directionality and strength of multiple secondary interactions.

Fractal-like self-assembly of oligo(p-phenylene vinylene) capped gold nanoparticles.

Reversible interparticle self-organization is reported for gold nanoparticles functionalized with an oligo(p-phenylene vinylene) moiety in butanol. The aggregates show a clear melting temperature at 80 degrees C, and atomic force microscopy and transmission electron microscopy indicate a fractal-like organization of the particles.

Synthesis of n-type perylene bisimide derivatives and their orthogonal self-assembly with p-type oligo(p-phenylene vinylene)s.

Four different (chiral) electron-deficient (n-type) perylene bisimides containing aliphatic, aromatic, or ethyleneoxide side chaines have been synthesized and fully characterized. All of them form supramolecular stacks in apolar methylcyclohexane (MCH) solution as demonstrated by concentration- and temperature-dependent absorption, circular dichroism, and fluorescence studies. One derivative was investigated in more detail in the solid state and proven to be liquid crystalline and capable of forming nanometer-sized fiberlike networks when drop-cast from MCH. Optical spectroscopy techniques show that perylene bisimide and an oligo(p-phenylene vinylene) (p-type) derivative orthogonally self-assemble into separate nanosized p-and n-type stacks in MCH. In contrast in toluene only molecularly dissolved species are present. In films deposited from MCH as well as from toluene photoinduced electron transfer takes place from the p-type material to the n-type material. As a result of the orthogonal self-assembly process, in films from MCH an ordered network of fibers was formed, whereas in films from toluene no ordering was observed. However, probably due to the lateral orientation on the surface and the presence of long aliphatic chains pointing toward the electrodes, efficient bulk heterojunction solar cells could not be constructed.

Transfer of pi-conjugated columnar stacks from solution to surfaces.

Three hydrogen-bonded oligo(p-phenylenevinylene)s, OPV3, OPV4, and OPV5, that differ in conjugation length have been synthesized and fully characterized. All three compounds contain chiral side chains, long aliphatic chains, and a ureido-s-triazine hydrogen bonding unit. (1)H NMR and photophysical measurements show that the OPV oligomers grow hierarchically in an apolar solvent; initially, dimers are formed by hydrogen bonds that subsequently develop into stacks by pi-pi interactions of the phenylenevinylene backbone with induced helicity via the chiral side chains. SANS measurements show that rigid cylindrical objects are formed. Stacks of OPV4 have a persistence length of 150 nm and a diameter of 6 nm. OPV3 shows rigid columnar domains of 60 nm with a diameter of 5 nm. Temperature and concentration variable measurements show that the stability of the stacks increases with the conjugation length as a result of more favorable pi-pi interactions. The transfer of the single cylinders from solution to a solid support as isolated objects is only possible when specific concentrations and specific solid supports are used as investigated by AFM. At higher concentrations, an intertwined network is formed, while, at low concentration, ill-defined globular objects are observed. Only in the case of inert substrates (graphite and silicium oxide) single fibers are visible. In the case of the repulsive surfaces (mica and glass), clustering of the stacks occurs, while, at attractive surfaces (gold), the stacks are destroyed.