Noori, Mohammed and Lambert, Colin (2017) Quantum Theory of Electron Transport Through Photo-Synthetic Porphyrins. PhD thesis, Lancaster University.
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Abstract
Optoelectronic properties of metallo-porphyrins play a central role in photosynthesis and are therefore crucial to life on earth. This thesis presents a series of studies into the electronic and thermoelectric properties of various families of molecular junction of metalloporphryins Two main techniques will be included in the theoretical approach; Density Functional Theory, which is implemented in the SIESTA code, and the Green’s function formalism of electron transport (Chapter 2), which is implemented in the GOLLUM code. Both techniques are used extensively to study a family of metallo-porphyrin molecules. In this thesis, I cover three main results in the areas of electical and thermoelectrical properties of metallo-porphyrin molecular wires, in which a Co, Ni, Cu, or Zn metal ion in the center of the porphyrin skeleton is coordinated to pyridyl moieties attached to gold electrodes and demonstrate that the current-perpendicular-to-the-plane (CPP) electrical conductances of the series of Ni, Co, Cu or Zn-5,15-diphenylporphyrins increase with the atomic weight of the divalent metal ion. This supramolecularly wired arrangement with the aromatic plane perpendicular to the current is stable at room temperature and provides a unique family of high-conductance molecular wires, whose electrical transport properties can be tuned by metal substitution. I deal with the thermoelectric properties of the same metallo-porphyrin junction (CPP) in chapter four, where I demonstrate that varying the transition metal-centre of a porphyrin molecule allows the molecular energy levels to be tuned relative to the Fermi energy of the electrodes thereby creating the ability to optimise the thermoelectric properties of metallo-porphryins. In chapter six I compare thermoelectric properties of three zinc porphyrin (ZnP) dimers and a ZnP monomer. The results show that the “edge-over-edge” dimer formed from stacked ZnP rings possesses a highest room temperature ZT ever reported for an organic material.