Surface-functionalized semiconducting nanoparticles in polymers: From self -assembly to functional materials
Seminconducting nanoparticles, also known as quantum dots or quantum rods depending on the shape, have unique optical and electronic properties. Polymers, on the other hand, have excellent processing properties. Therefore, it is desirable, in many cases, to integrate nanoparticles in polymers. The surface chemistry of nanoparticles is the key for them to be integrated into a polymer matrix in a controlled way. Nanoparticles are generally covered with alkyl ligands directly from typical synthetic procedures and surface modification is required to provide them with desired surface chemistry. First, water-soluble cadmium selenide (CdSe) nanoparticles and nanorods were made by modifying nanoparticle surfaces with charged ligands or poly(ethylene oxide) ligands and these water-soluble nanoparticles were selectively assembled into the holes and channels of nanotemplates fabricated from diblock copolymers.
Second, nanoparticle surfaces were functionalized with ligands (e.g., poly(ethylene oxide)) that were compatible with a polymer matrix (e.g., poly(methyl methacylate)) such that the nanoparticles were well-dispersed into the polymer matrix and a self-healing bilayer material was developed using these well-dispersed nanoparticle-filled polymer matrix.
Third, CdSe nanorods were oriented normal to a substrate in regioregular poly(3-hexylthiophene) matrix. However, the oriented CdSe nanorods were found to phase separate from poly(3-hexylthiophene) matrix. Then, chemistry was developed to synthesize vinyl-terminated poly(3-hexylthiophene) and Heck coupling was used to attach vinyl-terminated poly(3-hexylthiophene) (hole transporting material) onto aryl bromide-covered CdSe nanorods (electron transporting material) for photovoltaic applications. The poly(3-hexylthiophene) functionalized CdSe nanorods showed the expected charge transfer between these two semiconductors, a prerequisite for an efficient photovoltaic material.
Stimulated by the design of poly(3-hexylthiophene)-functionalized CdSe nanorods, donor-acceptor poly(3-hexylthiophene)-b-poly(perylene diimide acrylate) block copolymer was synthesized. This block copolymer also showed photoluminescence quenching in solid states.