Molecular electronic properties of fused rigid porphyrin-oligomer molecular wires

Porphyrin-derived materials may be linked together by fusion to rigid coplanar aromatic bridges such as substituted anthracenes to form linear or branched oligomers. Here, we consider linear oligomers of free-base porphyrin and meso-tetra-aryl derivatives, such as the tetramer. Previously, a number of semi-empirical quantum-chemical methods have been used to determine the geometries and electronic structures of the ground and excited electronic states. Here, the inter-ring coupling responsible for electron or hole conduction is discussed as a function of oligomer size and the predicted molecular-wire characteristics outlined. Comparisons with properties of other linear molecular wires are summarized, and possibilities of introducing switching capacity are indicated. It should be noted that the edge-to-edge length of the tetramer is ca. 56 إ, sufficient for trans-membrance spanning, while the length of the octamer, ca. 110 إ, is sufficient for nano-electrode spanning.