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The aim of this thesis is to apply in situ infrared spectroscopy to improve our understanding of electrocatalytic CO2 reduction (a potential technology for renewable energy storage and synthesis of fuels) in ionic liquid-water mixtures. Imidazolium-based ionic liquids reportedly enable low overpotential CO2 reduction compared to conventional aqueous electrolytes. However, there is no agreement on the mechanism. In situ spectroscopy has enhanced our knowledge of aqueous systems but has scarcely been used with ionic liquid-water mixtures. This work shows that CO is the main adsorbed product of CO2 reduction on Au electrodes, like in aqueous media. Experiments yielded no evidence of intermediates proposed in the literature. The spectra revealed hydrogen-bond-free water and bulk-like water populations in the mixture. Theoretical work predicts that hydrogen-bond-free water may stabilise the CO2-radical and account for the low overpotentials. However, experiments with varying mol% ionic liquid-water mixtures provided no evidence to support this. A study on Pt electrodes revealed that exposed areas of the Si substrate beneath the Pt film generate an infrared signal assigned to SiHx in the same spectral region as adsorbed CO or H atop Pt. The potential dependence of the band indicates that parts of Si formed ohmic contact with the metal. The significance of this work is, first, to question theories on CO2 reduction intermediates in ionic liquids by failing to detect species proposed in the literature. Second, it shows that the interfacial behaviour of water populations is complex and worth investigating in more depth. Third, the results emphasise the importance of performing careful blank experiments on ionic liquid systems, because signals may be confused for intermediates of CO2 reduction or other electrocatalytic processes.

Reduced nicotinamide adenine dinucleotide (NADH) is the main electron donor in energy-related metabolic processes. NADH in cells exists as two conformations, taking a folded conformation when free and an unfolded conformation when protein bound. The local concentration of free NADH is physiologically significant and is an important parameter in energy-related metabolism because it determines the chemical reaction velocity. This work explores changes in intracellular NADH conformation when cells are subject to different metabolic regulators. Metabolic regulators (KCN, glucose, ethanol, FCCP, and O2) are used to change the metabolic status of the Saccharomyces cerevisiae. Intracellular NADH is excited at 337 nm using a nitrogen laser, and any wavelength shift in the excited-state emission is used to assess a change NADH conformation. The emission centroid wavelength and the emission intensity are recorded in real time. Results suggest that when NADH concentration increases or decreases due to the addition of a metabolic regulator, the proportion of free NADH in the NADH pool also increases or decreases.

In this thesis, the coherent nonlinear optical spectroscopy of negatively charged interface fluctuation GaAs/Al0.3Ga0.7As quantum dots is studied by utilizing differential transmission techniques in both frequency and time domains. In the frequency domain, a spectral hole burning (SHB) method with two independently tunable frequency-stabilized continuous wave lasers is employed to eliminate the broad inhomogeneous broadening effect. In SHB experiments, not only the stimulated Raman spin coherence is excited and measured, but spin population pulsation is also demonstrated. Both electron decoherence and population relaxation times (∼ 3 nsec) are extracted from the SHB experiments, which are theoretically discovered to be limited by the spin spectral diffusion processes. A novel nonlinear coherent optical phase-modulation spectroscopy is developed to measure the real electron spin relaxation time. Since the phase-modulation measurement is only sensitive to processes with relaxation rates on the same order or slower than the modulation rate, the relatively slow electron spin-flip relaxation process is distinguished from the fast spectral diffusion processes. The measured result of the electron spin-flip relaxation rates as a function of magnetic field and temperature is best explained in term of spin relaxation processes by the phonon-assisted Dresselhaus spin-orbit scattering. The spin-flip relaxation time approaches 46 musec for zero magnetic field at 4.5 K. With the help of sub-micron aperture arrays on the sample surface, coherent nonlinear optical response in the frequency domain is clearly observed in a single charged QD with magnetic field in both Faraday and Voigt geometries. The optically forbidden transitions are optically excited and detected experimentally through the spin ground state mixing with an applied in-plane magnetic field. Pauli blockade of the electron spins is clearly observed when the system is excited with different polarization. In addition, extremely long quantum beat oscillations due to the long spin Raman coherence excited through a sub-micron aperture are demonstrated using ultrafast laser pulses. By analyzing the dependence of the amplitude and phase of the quantum beat oscillations at various magnetic fields, it is evident that the spin Raman coherence not only arises from optical stimulated Raman transitions, but also from spontaneously generated coherence due to the trion population relaxation.