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Chemical hybridization of fullerenes, [pi]-electron systems and inorganic nanomaterials

Authors Liu, Dongfang
Issue Date 2008
Summary Buckminsterfullerenes have been conjugated to CdSe nanocrystals by exchanging TOPO ligands on the CdSe nanocrystals with C60-bound dithiocarbamate ligands. To improve solubility of the C60-capped CdSe nanocrystals, a small molecular weight dithiocarbamate ligand was used as co-ligand in the ligand exchange reaction. The as synthesized (C60)8-CdSe conjugates were purified by dialysis against ethanol and characterized by 1H NMR, UV-vis and TEM. Photoelectrochemistry of a film cast from the (C60)8-CdSe conjugate revealed a significantly enhanced photocurrent compared with the film of CdSe-TOPO nanocrystals as well as that of C60 alone, suggesting that our conjugation strategy is viable for efficient photo-induced charge separation, transport and collection. C60 has been conjugated to PbSe by using the similar strategy to that of the C60-CdSe nanoconjugate in Chapter 1. The as synthesized C60-PbSe conjugates were characterized by H NMR, UV-Vis and TEM. The H NMR study shows that the dithiocarbamate ligands has stronger interaction with PbSe nanocrystals than that with CdSe nanocrystals. Photoelectrochemistry of a film cast from the C60-PbSe nanoconjugate revealed a cathodic photocurrent, although the individual C60 and PbSe nanocrystals generated anodic photocurrent respectively. The reversed polarity of the photocurrent suggesting the C60 can serve as p-dopants to the PbSe nanocrystals through the surface transfer doping process. A Cu(I)-assisted C60-polymerization method has been developed for the seamless coating on nanosized objects of Cu2O, forming novel Cu2O-C60 core-shell nanostructures. It is based on a reaction of C60 and ethyl isocyanoacetate to form polymerized fulleropyrolines, catalyzed by and thus coated on the Cu2O nanomaterials. Cu2O nanoribbons and nanocubes were used in this work to demonstrate the nano-coating method. The Cu2O-C60 core-shell nanostructures were characterized comprehensively, revealing a uniform, covalently-polymerized C60 shell that closely sheaths the Cu2O nanostructures. Details of the Cu(I)-assisted C60-polymerization process are proposed, which combines the solution chemistry and surface chemistry of C60. The Cu2O cores in the composite nanocubes could be removed, yielding monodispersed C60 nanoboxes. Preliminary measurements demonstrated enhanced photocurrent of the Cu2O-C60 nanoribbons arrayed on Cu foil compared to that of the Cu2O nanoribbons. Two strategies have been explored for organic functionalizations of ZnO nanotetrapods via anchor groups of carboxylate and phosphonate. With these methods, oleyl chains were assembled on surfaces of the ZnO nanotetrapods, significantly enhancing their solubility in nonpolar solvents, such as chloroform and toluene. The surface functionalization strategies have been extended to electroactive and photoactive molecules such as protoporphyrin and C60 on the ZnO nanotetrapods. The surface modified ZnO nanotetrapods were characterized comprehensively, revealing a uniform, covalently linked monolayer assembled on the surface. This work opens a broad perspective for the application of the organically functionalized nanotetrapods in optoelectronics and biomedicine. Two-photon luminescence (TPL) spectra were measured to study the effect of protoporphyrin and C60 to TPL properties of ZnO nanotetrapods. The results show that after modifying with protoporphyrin, the exciton emission of the ZnO nanotetrapods was red-shift for about 30 nm, which may be due to the surface charge transfer doping of protoporphyrin to ZnO nanotetrapods. After modified with C60, the TPL spectrum of ZnO nanotetrapods was obviously enhanced to the exposure of laser with the intensity of 140 mW. The stable C60-ZnO nanocomposites may have applications in the nonlinear optical devices.
Note Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2008
Language English
Format Thesis
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