In Silico Design and Synthesis of Small-Molecule Intrinsic Organic Semiconductors for Organic Electronics

On a global scale, the mass production of organic semiconductors for electronic applications in flexible display technology, among others, is linked to both research and consumer demand. To overcome challenges, the fabrication of the organic electronic devices has moved from high cost small-molecule vapour-phase deposition type techniques, to relatively low cost solution processing of the organic thin film transistors (OTFTs). Initial studies in this work focused on the modelling, prediction and synthesis of two dimensional planar structures. These studies probed the isomeric structures of pentacene. Quantum mechanics/density functional theory calculations found that at least five out of a total of 12 isomers (inclusive) are both air stable and have the same order of magnitude for the hole and electron rates of charge transfer as that of pentacene; suggesting that isomeric candidates of the initial target structure are worthy of thorough investigation. A second study on planar structures focused on novel and rationally designed molecules, six isomers inclusive, in an attempt to develop a challenging but high performing seven fused ring heteroacene. The study gave the interesting result that one structure is suitable for not just OTFTs, but also non linear optics, inferring that highly functional optoelectronic switches are possible from a single OTFT. A small library of rod-like structures were probed to contrast with the nature of the structures investigated so far. These contain linear components that separate the planar aromatic components in the molecules. It was discovered that these structures are highly flexible and soluble in common organic solvents, showing promise for applications as solution processed OTFTs. In summary, key discoveries of the study include (i) world-class candidates could be out-competed by their own isomers; (ii) new heteroacenes conceived could have bifunctional outputs for two separate fields in organic electronics; (iii) novel molecular rods were synthesised and found to have excellent solubility in common organic solvents, thereby enabling large scale fabrication of flexible display technologies.