The overarching theme of this thesis involves the investigation of the electronic structures of porphyrin and phthalocyanine derivatives and the predictable manipulation of their molecular orbital energy levels induced via changes in aromatic macrocyclic structure, peripheral substitution, or axial ligation. Using both experimental spectroscopic (UV-vis, circular dichroism, magnetic circular dichroism) and theoretical (density functional theory and time-dependent DFT) techniques, the electronic structures of these macrocyclic systems were studied to provide tunable platforms to best suit their specific applications. Intended outcomes for these compounds include their use as photosensitizers for the photodynamic therapy of cancer, chemical sensors, and molecular wires.