Studies of Metal-Organic and Organic Charge-Transport for Plastic Opto-Electronics

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0309131MarderThe aim of this program is to improve the state-of-the-art of molecular charge-transport agents by: i) developing an understanding of the relative importance of disorder and reorganization energy in high-mobility materials and ii) developing high-mobility materials. This will be accomplished by minimizing reorganization energy by using systems with more-or-less non-bonding frontier orbitals, and by using systems with highly delocalized frontier orbitals; maximizing intermolecular electronic coupling by using systems with diffuse orbitals delocalized towards the periphery of the molecule, by using species capable of more isotropic overlap than typical organic charge-transport agents, and by using columnar discotic liquid-crystalline materials.To minimize reorganization energy, the energy required to move the electron whilst leaving nuclei frozen, systems should be selected in which the frontier orbitals have little bonding or anti-bonding character, or in which they are extensively delocalized. Removal of electrons from metal based orbital in organometallic compounds will be investigated in this regard. To maximize orbital overlap two approaches will be pursued. Firstly, organometallic and coordination compounds with rather more three-dimensional shapes (e.g. octahedral, tetrahedral) than most organic charge-transport agents (which often contain basically planar cores; e.g. the biphenyl unit in TPD) will be investigated. In this way, it is anticipated that the overlap will not be dependent upon orientational factors in glassy media; i.e. that overlap between nearest neighbor molecules will always be good. Moreover, these materials are likely to form isotropic glasses with isotropic mobilities, which will be useful in some devices. This second approach involves examination materials that self-organize into columnar discotic mesophases in which overlap along the column of molecules is maximized. In the process of performing this research students will receive an interdisciplinary training, working on both synthesis and physical measurements.