Hybrid semiconductor nanoparticles: π-conjugated ligands and nanostructured films

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.