Computational techniques, mostly density functional theory (DFT), were applied to study metal-based catalytic processes for energy conversion reactions. In the first and second projects, the main focus was on activation of the light alkanes such as methane, which have thermodynamically strong and kinetically inert C–H bonds plus very low acidity/basicity. Two Mo-oxo complexes with the different redox non-innocent supporting ligands, diamide-diimine and ethylene-dithiolate, were modeled. These Mo-oxo complexes are modeled inspired by active species of a metalloenzyme, ethylbenzene dehydrogenase (EBDH). The results for the activation of the benzylic C–H bond of a series of substituted toluenes by modeled Mo-oxo complexes show there is a substantial protic character in the transition state which was further supported by the preference for [2+2] addition over HAA for most complexes. Hence, it was hypothesized that C–H activation by these EBDH mimics is controlled more by the pKa than by the bond dissociation free energy of the C–H bond being activated. The results suggest, therefore, promising pathways for designing more efficient and selective catalysts for hydrocarbon oxidation based on EBDH active site mimics. Also, it is found that the impact of supporting ligand and Brønsted/Lowry acid/base conjugate is significant on the free energy barrier of …

Donor-acceptor systems have unique properties that make them ideal candidates for solar energy harvesting through mimicry of natural photosynthesis. This dissertation is focused on unraveling those unique properties in various types of donor-acceptor systems. The systems investigated are categorized as closely linked, push-pull, supramolecular, and multi-unit. As part of the study, photosynthetic analogues based on BF2-chelated dipyrromethene (BODIPY), porphyrin, phthalocyanine, truxene, ferrocene, quinone, phenothiazine (PTZ), perylenediimide (PDI), fullerene (C60), dicyanoquinodimethane (DCNQ), tetracyanobutadiene (TCBD), and triphenylamine (TPA) are investigated. The effects of proximity between donor-acceptor entities, their geometrical orientation relative to each other, push-pull character of substituents, and competitive energy and electron transfer are examined. In all systems, primary events of photosynthesis are observed, that is absorption and energy transfer and/or electron transfer is witnessed. Ultrafast transient absorption spectroscopy is utilized to characterize the photo-induced events, while other methods such as steady-state luminescence, cyclic voltammetry, differential pulse voltammetry, chronoamperometry, and computational calculations are used to aid in the characterization of the donor-acceptor systems, in particular their applicability as solar energy harvesters.