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UBC Theses and Dissertations

Gold and cadmium selenide (CdSe) nanoparticles capped with oligothiophenes Sih, Bryan Christian

Abstract

The preparation and characterization of hybrid materials composed of oligothiophene-capped Au and CdSe nanoparticles with novel chemical, structural, electronic and optical properties are reported. α-Phosphino-oligothiophenes (12-15 and 23) and thiol-substituted oligothiophenes (26, 29, 32) were prepared by metal-catalyzed coupling reactions and studied using absorption and emission spectroscopy, and cyclic voltammetry. These functionalized oligothiophenes were used to passivate the surface of Au (16-19) and CdSe (CdSe-26, CdSe-29, CdSe-32) nanoparticles. Oligothiophene-capped Au nanoparticles were prepared directly by reducing a Au salt in the presence of the phosphino-oligothiophene. Attachment to the Au nanoparticles has little effect on the electronic structure of the oligothiophene as determined from the absorption spectra. On the other hand, the oligothiophenes appear to affect the electronic structure of the Au nanoparticle, as observed via a red-shift in the surface plasmon absorption. Electrochemical oxidation of the phosphino-terthiophene capped Au nanoparticles lead to crosslinking where the nanoparticles are linked both structurally and electronically by observed increases in conjugation, conductivity and plasmon coupling relative to the unlinked particles. The oligothiophene bridge linking the Au nanoparticles is shown to facilitate plasmon coupling between adjacent nanoparticles. The crosslinked material also demonstrates tunable conductivity where the conductivity in the material can be increased by oxidative doping of the π-conjugated bridge. Oligothiophene-capped CdSe nanoparticles were prepared through an exchange reaction between thiol-substituted oligothiophenes and trioctylphosphine oxide-capped CdSe nanoparticles. Attachment of the oligothiophenes to the CdSe nanoparticle has little effect on the electronic structure of the oligothiophene as determined from the absorption spectra. However, the optical properties are significantly affected where the oligothiophene emission is quenched after attachment to the CdSe surface due to either an energy or electron transfer mechanism. Depending on the number of oligothiophenes attached to the CdSe surface, the optical properties of the CdSe nanoparticles are affected differently. An excess number of thiols act as hole traps leading to quenching of the nanoparticle emission. Attempts to electrochemically crosslink these oligothiophene-capped CdSe nanoparticles were unsuccessful possibly due to the intrinsic resistivity in the particles.[See Thesis for Diagrams]

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