Amphiphilic dendron-rod molecules with three hydrophilic poly(ethylene oxide) (PEO) branches attached to a hydrophobic octa-p-phenylene rod stem were investigated for their ability to form two-dimensional micellar structures on a solid surface. A treelike shape of the molecules was reported to be a major factor in the formation of nonplanar micellar structures in solution and in the bulk state (cylindrical and spherical). We observed that in these treelike amphiphilic molecules the hydrophilic terminated dendron branches assemble themselves in surface monolayers with the formation of two-dimensional layered or circular micellar structures. We suggested the formation of the planar ribbon-like structures with interdigitated layering within the loosely packed monolayers and circular, ringlike structures (2D circular aggregates) in the precollapsed state.
Hybrid inorganic–organic colloidal nanoparticles can be designed to achieve specific and complementary optoelectronic properties different from their sole organic and inorganic counterparts. The efficient coupling between organic and inorganic moieties facilitates optimization of these optoelectronic properties as single particles. Simply dispersing inorganic nanoparticles in an organic (polymer) matrix permits nanocomposite formation, but are usually prone to phase segregation. To achieve more-efficient energy transfer, charge carrier transport, and correspondence between energy levels of the inorganic and organic moieties, direct coupling is necessary. Ligand exchange with highly π-conjugated organic ligands or polymerization of optoelectronically active organic polymer on the surface of the inorganic nanoparticles, results in core–shell-like structures. This increases the surface-area-to-volume ratio contact between organic and inorganic moieties. Because of this advantage, energy transfer mechanism in hybrids can be tuned more efficiently for radiative or nonradiative decay. Recombination of excitons (bound electron–hole pairs) or the isolation of electrons (modulating charge transport) by controlling the conduction band-valence band (highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO)) level becomes more tunable in donor–acceptor materials systems. Such optoelectronic property fine-tuning in a hybrid colloidal system can also be applied toward ultrathin film preparation and two-dimensional patterning (e.g., photovoltaic systems, light-emitting diode materials, sensors, and patterned arrays). A compatible organic shell facilitates greater solubility and dispersion of the inorganic core in a host polymer matrix. The use of a dendronic ligand provides an interesting method for facilitating surface functionalization, nanoparticle solubility, and electrochemical reactivity. By focusing on chalcogenide and semiconductor nanocrystals (NCs) or quantum dots (QDs), it is possible to limit these properties directly to charge carrier transport and energy transfer mechanisms. Each hybrid nanoparticle in essence carries the same properties replicated or dispersed within a film or a pattern. This review focuses on the design, preparation, and properties of such nanomaterial systems.
Carbazole containing ligand dendrons are designed based on second generation polybenzyl ether dendrons (2GPO). This is subsequently used for directly synthesizing and capping CdSe nanoparticles in contrast to ligand exchange for introducing functionality. The stable hybrid CdSe‐2GPO quantum dot nanoparticles have characteristic energy‐transfer properties from the donor carbazole peripheral groups to the acceptor CdSe nanoparticles, i.e., overlap of the fluorescence of the carbazole with the absorbance of the CdSe nanoparticle resulting in an enhanced fluorescence with concentration through Förster resonance energy transfer (FRET). However, electropolymerization of the peripheral electroactive carbazole units result in a red‐shift in absorbance and quenching in fluorescence. This is attributed to a reversed molecular orbital energy order with respect to the electropolymerized carbazole dendron and CdSe nanoparticle. The hole‐transfer results in fluoresence quenching and charge transfer between the CdSe nanoparticles and the polycarbazole peripheral units. The photoelectric alteration may yet provide for an interesting electro‐optical or sensing device application based on electrochemical properties of the hybrid material.
The photopatterning of CdSe quantum dots (QDs) films is facilitated by preparing defect-rich QDs on selective sites on the film. A key step is UV irradiation in the presence of a polar solvent such as methanol in situ as a "developer" which readily dissolves trioctylphosphine oxide (TOPO) but not the QDs. This results in a dramatically reduced photopatterning time and irradiation intensity requirement. The optical property changes were examined by UVÀvis and fluorescence spectroscopy. Furthermore, the photo-oxidized pattern of the CdSe QD film was readily observed by fluorescence microscopy. The chemical change due to attenuation of the PdO vibration of TOPO (due to its removal) could be detected by FT-IR imaging or FT-IR chemical mapping. Thus, the protocol is a simple yet effective way of patterning PL properties of QD films at much reduced exposure time compared to previously reported methods. It may find utility for a host of cellbased film assays and PL display device applications at various resolutions.
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