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The research presented in this thesis makes use of theoretical/computational techniques to calculate nonlinear spectroscopic signals and molecular volumes. These techniques have become more practical with advances in computational resources and now are an integral part of research in these areas. Preliminary results allude to the power of these techniques when applied to relevant problems and suggest that much progress can be made in understanding the complex nature of nonlinear spectroscopic signals and molecular volume contributions. The nonlinear spectroscopy work involves writing the quantum mechanical response functions in terms of classical time correlation functions which are amenable to calculation using classical molecular dynamics. The response functions reported in this thesis include the fifth order response function, probed in the fifth order Raman experiment, and the third order response function probed in the two dimensional infrared experiment. The molecular volume calculations make use of modern algorithms used in molecular dynamics simulations to calculate the full thermodynamic volumes of molecules.

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This thesis presents an exploration of the photophysics of colloidal semiconductor nanocrystals using both linear and non-linear optical measurement techniques. These optical methodologies are used to follow population dynamics in both singly and multiply excited nanocrystal systems as well as determine material properties of the ensemble. Topics covered in the thesis include, the identification and characterization of bulk-like nanocrystals, study of the fine structure states of the lowest energy exciton, single and multiexciton population dynamics, acoustic phonon modes, elasticity and surface stress properties of a colloidal ensemble in solution.Through linear spectroscopy, the properties of both quantum confined and bulk-like colloidal semiconductor nanocrystals are compared. The identification of a model system of bulk-like nanocrystals with a non-standard absorption profile serves to resolve an ambiguity in literature concerning their characterization. The remainder of the thesis is focused on the size-dependent properties of quantum confined CdSe colloidal nanocrystals. The population dynamics and material properties of these systems are studied using a nonlinear optical technique called transient grating. A third order transient grating measurement with a cross-polarized configuration, which follows the relaxation within the fine structure levels of the lowest energy exciton state, is demonstrated and used to compare systems with different crystal field splittings. Transient grating experiments performed with specific polarization sequences allow for selective observation of the dynamics amongst nearly degenerate levels at room temperature. Cross-polarized transient grating is also used to observe a quantized acoustic phonon mode in a series of nanocrystal samples. The observation of this mode allows experimental determination of the elasticity and surface stress of the nanocrystal ensemble in solution. The anisotropic origin of the acoustic phonon is discussed using a combination of theoretical analysis, modelling and experimental data. In addition, third- and fifth-order transient grating experiments are used to study exciton and multiexciton population relaxation dynamics. The work presented here spans the optical and material properties of quantum confined and `bulk' nanocrystals. This thesis attempts to illustrate the broad scope of the observed behaviour of colloidal nanocrystal systems and to contribute to a greater understanding of their physical properties.

This thesis presents an exploration of the photophysics of colloidal semiconductor nanocrystals using both linear and non-linear optical measurement techniques. These optical methodologies are used to follow population dynamics in both singly and multiply excited nanocrystal systems as well as determine material properties of the ensemble. Topics covered in the thesis include, the identification and characterization of bulk-like nanocrystals, study of the fine structure states of the lowest energy exciton, single and multiexciton population dynamics, acoustic phonon modes, elasticity and surface stress properties of a colloidal ensemble in solution.Through linear spectroscopy, the properties of both quantum confined and bulk-like colloidal semiconductor nanocrystals are compared. The identification of a model system of bulk-like nanocrystals with a non-standard absorption profile serves to resolve an ambiguity in literature concerning their characterization. The remainder of the thesis is focused on the size-dependent properties of quantum confined CdSe colloidal nanocrystals. The population dynamics and material properties of these systems are studied using a nonlinear optical technique called transient grating. A third order transient grating measurement with a cross-polarized configuration, which follows the relaxation within the fine structure levels of the lowest energy exciton state, is demonstrated and used to compare systems with different crystal field splittings. Transient grating experiments performed with specific polarization sequences allow for selective observation of the dynamics amongst nearly degenerate levels at room temperature. Cross-polarized transient grating is also used to observe a quantized acoustic phonon mode in a series of nanocrystal samples. The observation of this mode allows experimental determination of the elasticity and surface stress of the nanocrystal ensemble in solution. The anisotropic origin of the acoustic phonon is discussed using a combination of theoretical analysis, modelling and experimental data. In addition, third- and fifth-order transient grating experiments are used to study exciton and multiexciton population relaxation dynamics. The work presented here spans the optical and material properties of quantum confined and `bulk' nanocrystals. This thesis attempts to illustrate the broad scope of the observed behaviour of colloidal nanocrystal systems and to contribute to a greater understanding of their physical properties.