Surface Functionalization Of Semiconductor Nanocrvstals And Their Composite With A Functional Polymer

In recent years, semiconductor nanocrystals （NCs） have attracted much attentiondue to their many unique optical properties, high surface-to-volume ratio and otherproperties related to their nanometer dimension. Their optical properties depend onnot only the particle size and morphology, but also on ions doping and surface state.The perfect degree for the surface state of nanocrystals can also affect their opticalproperties. The stability and dispersion of nanocrystals can be improved through thesurface engineering realizing the functionalization of nanocrystals. The opticalproperties of nanocrystals can also be tuned by the energy transfer or electron transferbetween nanocrystals and the organic functionalized ligands or chromophore on thesurface of nanocrystals. So tailoring the optical properties of nanocrystals through thesmall molecules functionalization on the surface of nanocrystals becomes one ofimportant development directions in this area.In this thesis, we used8-hydroxyquinoline and its derivatives as the organicsmall molecule ligands, and established the effective methods for the surfacefunctionalization of nanocrystals with these small molecules. The synergistic effect ofoptical properties between these molecules and nanocrystals were investigated and themechanism for tuning the optical properties of nanocomposites by these moleculeswas explored. We also designed and synthesized a functional and luminescentconjugated polymer which has good compatibility and synergistic optical propertieswith the functionalized nanocrystals, and the effect of their interaction on thephotophysical properties of bulk nanocomposite materials was studied. The detailedcontent of this thesis includes:1. We presented a simple and novel method for the preparation of QS-ZnS:Mncomposite nanocrystals from Mn2+-doped ZnS NCs through the surface chelating of8-hydroxyquinoline-5-sulfonic acid （HQS）. The emission colors of the novel NCscomposite can be tuned from orange to cyan by carefully controlling the dosage ofHQS. The efficient white light-emitting NCs with color coordinates （0.35,0.34） can be carried out, which light was very close to pure white light. The white lightemission is contributed to the surface-coordination emission and dopant emission ofNCs host.2. We synthesized CdSe/ZnS core-shell NCs and Cd_1-xZn_xSe_1-yS_yNCs withasymptotic chemical composition structure by high-temperature implantation method,and then the8-hydroxyquinoline （HQ）,4-hydroxy-1,5-naphthyridine （ND） and5-（2-methacryloylethyloxymethyl）-8-quinolinol （MQ） with the importantoptoelectronic applications were used as the ligands to functionalize the surface ofNCs via ligand exchange process. The study found that the structures and ratios of thefunctional ligands had an important effect on the photophysical properties of theresultant NCs. The charge separation and recombination process were observed in thefunctionalized Cd_1-xZn_xSe_1-yS_yNCs, which can lead the luminescent intensity ofnanocomposites weaken even quench. The ligands with electron-withdrawingproperties and the increasing surface ligand concentration can enhance the chargerecombination rate. However, for the CdSe/ZnS core-shell NCs, increasing ZnS shellthickness of NCs can decrease the charge recombination rate, and improve theluminous efficiency of NCs. We hope that these surface-functionalized NCs can bepotentially used in the design and fabrication of electroluminescence and photovoltaicdevices。3. We adopted a new synthetic strategy and successfully synthesized a type ofnovel conjugated/nonconjugated PPV derivatives containing the styrene group andcarboxyl group in the side chains. The possible reaction mechanism was proposed.We also dispersed the novel polymer into styrene, mixed with CdSe/ZnS core-shellNCs obtained by high-temperature implantation method. Then, the mixture wascopolymerized with5-（2-methacryloylethyloxymethyl）-8-quinolinol, and the bulknanocomposites with white light emission were obtained. The white light emissionoriginate from the trichromatic superposition of emission PPV derivative （blue）,CdSe/ZnS NCs emission （red） and the surface-coordination emission （green）.