Polymers as Multidentate Ligands for Surface Modification and Hierarchical Organization of Colloidal Quantum Dots

This thesis describes the design and synthesis of homopolymers and copolymers for tuning surface properties of colloidal semiconductor quantum dots (QDs), and directing QD self-assembly to create well-defined 3D structures in which the spatial organization of QDs and other functional materials (e.g. conjugated polymers) is properly controlled. A common feature of all of the polymers described in this thesis is that they contain multiple pendant anchoring groups such as tertiary amines, pyridines and acrylic acids, which bind strongly to QD surfaces as multidentate ligands. This thesis starts by describing a quantitative analytical method based on size exclusion chromatography (SEC) to characterize the interaction of poly(2-N,N-dimethylaminoethyl methacrylate) (PDMA) with TOPO-coated CdSe QDs. In addition, the separation of polymer-bound QDs from excess free polymer can be scaled up by preparative high-performance liquid chromatography. The second part of this thesis explores a method to disperse CdSe and core/shell CdSe/ZnS QDs into water using a poly(ethylene glycol-b-N,N-dimethylaminoethyl methacrylate) (PEG–b–PDMA) diblock copolymer. Alternatively, statistical copolymers, such as poly(oligoethyleneglycol)-co-PDMA (POEG-co-PDMA) and poly(N,N-dimethylacrylamide)-based statistical copolymers carrying pendant pyridine or imidazole groups play the same role as PEG–b–PDMA for dispersion of the QDs into water. The third part of this thesis describes the synthesis and characterization of a water-soluble pH-responsive PDMA-grafted polythiophene (denoted as PT-g-PDMA). The relatively rigid and extended conformation of the polythiophene backbones provides new opportunity for studying the correlation of between optical responses of conjugated polymers and their conformational transitions. In addition, the favorable interaction between the PDMA arms of PT-g-PDMA and CdSe nanorods allows enhanced interface-compatibility of the nanorods with the polythiophene backbone. The last part of this thesis presents a straightforward and versatile approach to achieving nanoscale co-organization of colloidal QDs (e.g. CdSe, CdSe/ZnS core/shell or PbS QDs) with conjugated polymers (e.g. poly(3-hexylthiphene)) by using polymer micelles of poly(styrene-b-4-vinylpyridine) as the structural motif. The spatially defined organization allows photoinduced excited state interaction between the QDs and poly(3-hexylthiphene) at the micellar interface, reminiscent of structures of light harvesting complexes in nature. This strategy is also applicable to other morphologies of polymer self-assemblies, such as poly(styrene-b-acrylic acid) (PS-b-PAA) vesicles.Ph