Pitt Logo LinkContact Us

Spectroscopic Investigations of Nanoscale Aggregates and Their Electron Transfer Properties in Solution

Wu, Mingyan (2011) Spectroscopic Investigations of Nanoscale Aggregates and Their Electron Transfer Properties in Solution. Doctoral Dissertation, University of Pittsburgh.

[img]
Preview
PDF - Primary Text
Download (4Mb) | Preview

    Abstract

    In part I, the changes in the absorption and fluorescence properties of poly-(p-phenylene-ethynylene) (PPE)-based conjugated polyelectrolytes were investigated as a function of the solution conditions such as concentration, temperature, solvent, surfactant, and the ionic strength. The equilibrium between unaggregated and aggregated forms of the polymer was described and quantified. The fluorescence quenching of polymers by positively charged and neutral macromolecules were also investigated and showed that the quenching depends on electrostatic, hydrophobic, and energy transfer interactions with the quencher. A detailed study using fluorescence correlation spectroscopy was performed and allowed us to probe the templating of a surfactant OTAB on the polyelectrolytes well below its critical micelle concentration. Furthermore, it was found that the optical and aggregation properties of these conjugated polyeletrolytes can be manipulated by changing the charge density along the polymer backbone. In part II, assemblies of CdSe and CdTe NPs were controlled by the electrostatic attraction of the charged functionalities placed on the NP surface coating. Electron transfer (ET) in assemblies of these NPs was studied in aqueous solution by fluorescence quenching. Three factors were found to determine how the ET depends on the nature of the NP assemblies by both steady-state and time-resolved fluorescence measurements: the interparticle distance, the energetic alignment of the NP bands (hence the size of the NPs), and the direction of the electric field between the NPs, created by their surface charges. In addition, the assemblies of CdSe NPs on a dithiol coated Au electrode were created and their electronic energetics were quantified. The energy level alignment of the filled and unfilled electronic states of CdSe NPs with respect to the Au Fermi level was investigated by both cyclic voltammetry and photoemission spectroscopy separately. These two measurements showed that the CdSe filled states become ‘pinned' to the Fermi level of the Au electrode. Furthermore, the preliminary electrochemical studies at the interface were carried out in order to investigate the organization and reactivity of nanoparticles/dyads at ITIES.


    Share

    Citation/Export:
    Social Networking:

    Details

    Item Type: University of Pittsburgh ETD
    ETD Committee:
    ETD Committee TypeCommittee MemberEmail
    Committee ChairWaldeck, David H.dave@pitt.edu
    Committee MemberLee, Jung-Kunjul37@pitt.edu
    Committee MemberSaxena, Sunilsksaxena@pitt.edu
    Committee MemberMeyer, Taratmeyer@pitt.edu
    Title: Spectroscopic Investigations of Nanoscale Aggregates and Their Electron Transfer Properties in Solution
    Status: Unpublished
    Abstract: In part I, the changes in the absorption and fluorescence properties of poly-(p-phenylene-ethynylene) (PPE)-based conjugated polyelectrolytes were investigated as a function of the solution conditions such as concentration, temperature, solvent, surfactant, and the ionic strength. The equilibrium between unaggregated and aggregated forms of the polymer was described and quantified. The fluorescence quenching of polymers by positively charged and neutral macromolecules were also investigated and showed that the quenching depends on electrostatic, hydrophobic, and energy transfer interactions with the quencher. A detailed study using fluorescence correlation spectroscopy was performed and allowed us to probe the templating of a surfactant OTAB on the polyelectrolytes well below its critical micelle concentration. Furthermore, it was found that the optical and aggregation properties of these conjugated polyeletrolytes can be manipulated by changing the charge density along the polymer backbone. In part II, assemblies of CdSe and CdTe NPs were controlled by the electrostatic attraction of the charged functionalities placed on the NP surface coating. Electron transfer (ET) in assemblies of these NPs was studied in aqueous solution by fluorescence quenching. Three factors were found to determine how the ET depends on the nature of the NP assemblies by both steady-state and time-resolved fluorescence measurements: the interparticle distance, the energetic alignment of the NP bands (hence the size of the NPs), and the direction of the electric field between the NPs, created by their surface charges. In addition, the assemblies of CdSe NPs on a dithiol coated Au electrode were created and their electronic energetics were quantified. The energy level alignment of the filled and unfilled electronic states of CdSe NPs with respect to the Au Fermi level was investigated by both cyclic voltammetry and photoemission spectroscopy separately. These two measurements showed that the CdSe filled states become ‘pinned' to the Fermi level of the Au electrode. Furthermore, the preliminary electrochemical studies at the interface were carried out in order to investigate the organization and reactivity of nanoparticles/dyads at ITIES.
    Date: 30 September 2011
    Date Type: Completion
    Defense Date: 03 June 2011
    Approval Date: 30 September 2011
    Submission Date: 22 July 2011
    Access Restriction: No restriction; The work is available for access worldwide immediately.
    Patent pending: No
    Institution: University of Pittsburgh
    Thesis Type: Doctoral Dissertation
    Refereed: Yes
    Degree: PhD - Doctor of Philosophy
    URN: etd-07222011-101340
    Uncontrolled Keywords: aggregates; conjugated polymer; electron transfer; nanoparticle; polyelectrolyte; solar cell.; spectroscopy
    Schools and Programs: Dietrich School of Arts and Sciences > Chemistry
    Date Deposited: 10 Nov 2011 14:53
    Last Modified: 06 Jan 2012 11:56
    Other ID: http://etd.library.pitt.edu/ETD/available/etd-07222011-101340/, etd-07222011-101340

    Actions (login required)

    View Item

    Document Downloads