AbstractsChemistry

In this thesis, structural effects on magnetic response properties: magnetically induced ring currents, the ESR g-tensor and hyperfine coupling tensor, and NMR chemical shifts, are investigated computationally with DFT methods, using various exchange-correlation functionals and basis sets. Magnetically induced currents are calculated for thieno-bridged porphyrins with the emphasis on the aromatic character of the systems, the degree of which is investigated for varying molecular modifications. The ESR g-tensor, as well as the hyperfine coupling tensors for Sn and O nuclei in the vicinity of a positively charged oxygen vacancy in solid tin dioxide, are reported with finite cluster methods using different cluster embedding techniques to define the structural environment. The NMR spectral trends for increasing-size nanoflakes of graphenic materials are predicted as functions of the size and boundary geometry of the flakes. Finally, a number of dye molecules are subjected to NMR chemical shift calculations where the intermolecular interaction effects present in liquid solution are studied with dynamic simulation techniques. The magnetically induced currents calculated for thieno-bridged porphyrins show that the changes in the molecular structure such as the direction of the thiophene ring or the substitution by Zn^2+ do not change the aromatic character of the molecule. It is possible to confirm the experimental assignment of the ESR signal with the g-factor around 2.00 to the positively charged vacancy in tin dioxide, whereas the other experimental assignment of a signal at g=1.89 is not supported by our calculations. Distinct characteristic NMR spectral patterns are found for graphene nanoflakes reflecting the effects of increasing size and different boundary geometries on the NMR shifts. Solvent effects on the NMR of dye molecules are found to be location-specific: nuclei from different regions of the systems display distinct response to solvation.