We investigate the ultrafast electronic excitation dynamics of phycobiliproteins from cryptophyte algae using two-dimensional electronic spectroscopy and frequency-resolved transient absorption spectroscopy. We detail the development of a transient absorption spectrometer that utilizes balanced and fast detection methods to reduce noise and maintain high temporal and spectral resolution. We observe coherent oscillations and attribute them to vibrational coherences using the wave packet formalism. Analysis of the dynamic Stokes shift and motion of the wave packet on the potential-energy surface indicate the coherences are predominantly situated in the excited electronic state of the protein. These measurements imply that the ultrafast energy transfer within phycobiliproteins is coupled to the vibrational motion of its constituent chromophores. We demonstrate the capability and necessity of multiple ultrafast spectroscopic techniques for determining the origin of coherent motion in photosynthetic light-harvesting complexes.

Charge transport in self-assembled gold nanoparticle (NP)-alkanedithiol (HS(CH2)nSH) systems are investigated using break-junctions. A remarkably simple and reproducible method to fabricate break-junctions using electromigration is described. Using the break-junctions, self-assembled NP systems are studied in two limits: (1) at the single-NP and (2) at the NP-array limits. Single-NP devices exhibit Coulomb-blockade (CB) conductance suppressions at low temperatures. Contrary to predictions of an Orthodox theory, temperature-dependence of conductance inside CB exhibits multiple activation energies (Ea): A small Ea at low temperatures, and a larger Ea at high temperatures. The small Ea is independent of NP size and is attributed to an energy state at the metal--molecule contact, whereas the larger Ea scales with NP size and is attributed to NPs' charging energy. Importantly, a significant (~5-100fold) discrepancy is observed between values of charging energies obtained from Ea and CB thresholds. To account for the discrepancy, a new model is proposed in which electrons can temporarily be localized at the energy states at the contacts and lose energy. The model is supported by ultraviolet photoelectron spectroscopy which shows energy states close to Fermi level likely arising from gold-thiolate bonds. A suitably modified Orthodox theory can successfully explain the experimental observations. These results underscore the critical role of metal--molecule contacts in influencing energy-profiles of molecular junctions. Resistance-temperature dependencies of alkanedithiol-linked NP films show evidence of a metal-insulator transition (MIT) as n is varied. The MIT occurs at n = 5 and is explained in the context of a Mott-Hubbard model. Furthermore, all metallic films exhibit temperature coefficients of resistance that are smaller than that of bulk gold, and all insulating films exhibit a universal behavior, R ~ exp[(T0/T)^p], with p = 0.65. These observations are discussed in terms of temperature-independent elastic scattering and competitive thermally activated processes, respectively. The ability to tune properties of NP films thru an MIT implies that materials near the transition may be viewed as semiconductors. To explore this analogy, application of these materials in fabricating field-effect transistors is briefly described. These results highlight the utility of NP films as a platform for studying charge transport.

Charge transport in self-assembled gold nanoparticle (NP)-alkanedithiol (HS(CH2)nSH) systems are investigated using break-junctions. A remarkably simple and reproducible method to fabricate break-junctions using electromigration is described. Using the break-junctions, self-assembled NP systems are studied in two limits: (1) at the single-NP and (2) at the NP-array limits. Single-NP devices exhibit Coulomb-blockade (CB) conductance suppressions at low temperatures. Contrary to predictions of an Orthodox theory, temperature-dependence of conductance inside CB exhibits multiple activation energies (Ea): A small Ea at low temperatures, and a larger Ea at high temperatures. The small Ea is independent of NP size and is attributed to an energy state at the metal--molecule contact, whereas the larger Ea scales with NP size and is attributed to NPs' charging energy. Importantly, a significant (~5-100fold) discrepancy is observed between values of charging energies obtained from Ea and CB thresholds. To account for the discrepancy, a new model is proposed in which electrons can temporarily be localized at the energy states at the contacts and lose energy. The model is supported by ultraviolet photoelectron spectroscopy which shows energy states close to Fermi level likely arising from gold-thiolate bonds. A suitably modified Orthodox theory can successfully explain the experimental observations. These results underscore the critical role of metal--molecule contacts in influencing energy-profiles of molecular junctions. Resistance-temperature dependencies of alkanedithiol-linked NP films show evidence of a metal-insulator transition (MIT) as n is varied. The MIT occurs at n = 5 and is explained in the context of a Mott-Hubbard model. Furthermore, all metallic films exhibit temperature coefficients of resistance that are smaller than that of bulk gold, and all insulating films exhibit a universal behavior, R ~ exp[(T0/T)^p], with p = 0.65. These observations are discussed in terms of temperature-independent elastic scattering and competitive thermally activated processes, respectively. The ability to tune properties of NP films thru an MIT implies that materials near the transition may be viewed as semiconductors. To explore this analogy, application of these materials in fabricating field-effect transistors is briefly described. These results highlight the utility of NP films as a platform for studying charge transport.

We investigate the ultrafast electronic excitation dynamics of phycobiliproteins from cryptophyte algae using two-dimensional electronic spectroscopy and frequency-resolved transient absorption spectroscopy. We detail the development of a transient absorption spectrometer that utilizes balanced and fast detection methods to reduce noise and maintain high temporal and spectral resolution. We observe coherent oscillations and attribute them to vibrational coherences using the wave packet formalism. Analysis of the dynamic Stokes shift and motion of the wave packet on the potential-energy surface indicate the coherences are predominantly situated in the excited electronic state of the protein. These measurements imply that the ultrafast energy transfer within phycobiliproteins is coupled to the vibrational motion of its constituent chromophores. We demonstrate the capability and necessity of multiple ultrafast spectroscopic techniques for determining the origin of coherent motion in photosynthetic light-harvesting complexes.

The heterogeneous oxidation of n-hexane soot surfaces by gas-phase ozone has been studied in a coated-wall flow tube connected to a mass spectrometer. Uptake measurements confirm earlier studies that the initial uptake is primarily non-catalytic and that the number of reactive surface sites is close to that of a full monolayer. The initial uptake kinetics exhibit an inverse dependence on ozone gas-phase concentration, as expected if the reaction proceeds via a Langmuir-Hinshelwood mechanism. Support for this reaction not being an Eley-Rideal process comes from the lack of temperature dependence of the initial uptake coefficient, and that a saturated surface coverage of adsorbed dodecane does not affect the kinetics. It is demonstrated that there is a strong similarity between the initial uptake kinetics for ozone loss on a wide variety of surfaces. This suggests that the reactions proceed through a common rate determining step, most likely involving adsorbed ozone molecules.

The heterogeneous oxidation of n-hexane soot surfaces by gas-phase ozone has been studied in a coated-wall flow tube connected to a mass spectrometer. Uptake measurements confirm earlier studies that the initial uptake is primarily non-catalytic and that the number of reactive surface sites is close to that of a full monolayer. The initial uptake kinetics exhibit an inverse dependence on ozone gas-phase concentration, as expected if the reaction proceeds via a Langmuir-Hinshelwood mechanism. Support for this reaction not being an Eley-Rideal process comes from the lack of temperature dependence of the initial uptake coefficient, and that a saturated surface coverage of adsorbed dodecane does not affect the kinetics. It is demonstrated that there is a strong similarity between the initial uptake kinetics for ozone loss on a wide variety of surfaces. This suggests that the reactions proceed through a common rate determining step, most likely involving adsorbed ozone molecules.

The increasing environmental impact of society has created the need for the modification of current and the implementation of new industrial processes which are less environmentally harmful. However, these new or modified processes must be less material-, time-, and cost-intensive such that they are more economically beneficial than the processes they are to supplant. The described research was inspired by these two ideas and is comprised of two projects, both focused on the creation of recyclable, CO2-switchable methods of separating organic compounds. The development and optimization of switchable water, a CO2-switchable ionic strength aqueous solvent is described. The solvent system, an amine/aqueous mixture, had the ability to switch from low to high ionic strength via the application and removal of CO2. This solvent system was able to achieve salting-out of water-miscible organics in comparable amounts to several inorganic salts typically used for salting-out. The switchable water system was explored for use in several industrial applications. A homogeneous catalysis recycling system was developed for the hydroformylation of styrene. A catalyst was able to be recovered and recycled five times with minimal loss of activity. The use of switchable water to expedite the settling of clay suspensions was also explored. Switchable water, when used as process water did not settle bulk clay solids as quickly as a CO2-only treatment, but did however increase the settling rate of small clay fines resulting in lower turbidities of the supernatant. The solvent could be recovered from settled clay suspensions and recycled up to three times. Finally, efforts towards the realization of CO2-switchable chiral resolving agents are presented. It is hypothesized that chiral nitrogenous bases could be used as switchable resolving agents by forming diastereomeric salt pairs with racemic alcohols via the application of CO2. After separation of the diastereomers, removal of CO2 would afford the resolved alcohol enantiomers and the chiral base. Efforts towards the synthesis of a library of chiral nitrogenous bases and the screening of their reactivity with CO2-treated alcohols are described. Several bases were generated, but the necessary reactivity between the bases and the racemic alcohols in the presence of CO2 was not observed. / Thesis (Ph.D, Chemistry) -- Queen's University, 2012-12-20 16:26:50.635

Poly (para-phenylenevinylene) (PPV), and its derivatives such as poly [2-methoxy, 5-(2'-ethyl-hexoxy)-1,4-phenylene vinylene] (MEH-PPV), are typical conjugated polymers. In order to implement conjugated polymers into processable electronics technologies, we must first understand their complex photophysical properties as their efficiencies depend on the balance between exciton recombination and charge carrier formation. The inherent complexities of these materials arise from entanglement of the pi-electron system with disorder and nuclear motions of the polymer backbone. This disorder breaks the polymer chain into conformational subunits which can couple, giving rise to a set of delocalized states formed by Coulombic interactions between proximate subunits. Characteristics of PPVs include high quantum yields, non-mirror image absorption and fluorescence line shapes, and large apparent Stokes' shifts. These properties are discussed in the context of the relationships between polymer conformation, electronic structure, coupling, disorder and polymer photophysics. These important influences are often manifest in the dynamics of what happens after photoexcitation. In this work, we present 3-pulse photon echo peak shift (3PEPS) studies of conjugated polymers in both solution and film. To elucidate timescales characteristic of relaxation processes, we have simulated the 3PEPS data simultaneously with absorption and fluorescence, observing a rapid localization of the exciton in the initial ~ 20 fs. Additional contributions to the decay of the peakshift are discussed. We also present transient anisotropy data for PPV polymers and oligomers which is compared to dynamics simulation for isolated chains of PPVs. This work demonstrates the influence of microscopic structure on ultrafast dynamics. We show that relaxation between exciton states can lead to rapid depolarization of the anisotropy, even though the spatial extent of exciton migration may be small. Generally, the connection between conformation and electronic structure is a theme throughout this thesis.

Scanning Tunneling Microscopy (STM) has been used to study the physisorption and chemisorption behaviour for three simple organic haloalkanes; 1,5 Dichloropentane (DCP), Bromomethane (CH3Br) and Chloromethane (CH3Cl)) on Si(100) 2x1, at temperatures ranging from 270 K to room temperature. The results were interpreted by Density Functional Theory (DFT) performed by collaborators at McGill University and the University of Liverpool. Physisorbed molecules of DCP were found to self assemble into stable lines aligned predominantly perpendicular to the Si dimer pair rows on the surface. A novel mechanism for line formation of Dichloropentane, termed, Dipole Directed Assembly (DDA), was elucidated by DFT calculations. For CH3Br three different patterns of dissociative attachment of reaction products (CH3 and Br/Cl) were observed, and assigned to three reaction pathways. These experimentally determined relative yields were used to obtain differences in reaction activation energy, Delta Ea, between the reaction pathways. These, in turn, were compared with computed differences in reaction barriers, Delta Eb, obtained ab initio for the same pathways by DFT. For CH3Cl, two single-molecule patterns of attachment were found, and a new reaction pathway for attaching CH3Cl in long chains of alternating CH3 and Cl was discovered. The mechanisms for chain growth were determined experimentally by examination of single molecular steps. This mechanism was explained ab initio by DFT to be the result of relative barrier heights for the possible chain-growth pathways.

Poly (para-phenylenevinylene) (PPV), and its derivatives such as poly [2-methoxy, 5-(2'-ethyl-hexoxy)-1,4-phenylene vinylene] (MEH-PPV), are typical conjugated polymers. In order to implement conjugated polymers into processable electronics technologies, we must first understand their complex photophysical properties as their efficiencies depend on the balance between exciton recombination and charge carrier formation. The inherent complexities of these materials arise from entanglement of the pi-electron system with disorder and nuclear motions of the polymer backbone. This disorder breaks the polymer chain into conformational subunits which can couple, giving rise to a set of delocalized states formed by Coulombic interactions between proximate subunits. Characteristics of PPVs include high quantum yields, non-mirror image absorption and fluorescence line shapes, and large apparent Stokes' shifts. These properties are discussed in the context of the relationships between polymer conformation, electronic structure, coupling, disorder and polymer photophysics. These important influences are often manifest in the dynamics of what happens after photoexcitation. In this work, we present 3-pulse photon echo peak shift (3PEPS) studies of conjugated polymers in both solution and film. To elucidate timescales characteristic of relaxation processes, we have simulated the 3PEPS data simultaneously with absorption and fluorescence, observing a rapid localization of the exciton in the initial ~ 20 fs. Additional contributions to the decay of the peakshift are discussed. We also present transient anisotropy data for PPV polymers and oligomers which is compared to dynamics simulation for isolated chains of PPVs. This work demonstrates the influence of microscopic structure on ultrafast dynamics. We show that relaxation between exciton states can lead to rapid depolarization of the anisotropy, even though the spatial extent of exciton migration may be small. Generally, the connection between conformation and electronic structure is a theme throughout this thesis.