Electronic delocalization in discotic liquid crystals: a joint experimental and theoretical study |
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Authors: | Crispin Xavier Cornil Jérôme Friedlein Rainer Okudaira Koji Kamiya Lemaur Vincent Crispin Annica Kestemont Gaël Lehmann Matthias Fahlman Mats Lazzaroni Roberto Geerts Yves Wendin Göran Ueno Nobuo Brédas Jean-Luc Salaneck William R |
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Affiliation: | Department of Physics and Measurement Technology, IFM, Link?ping University, S-58183 Link?ping, Sweden. xavcr@itn.liu.se |
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Abstract: | Discotic liquid crystals emerge as very attractive materials for organic-based (opto)electronics as they allow efficient charge and energy transport along self-organized molecular columns. Here, angle-resolved photoelectron spectroscopy (ARUPS) is used to investigate the electronic structure and supramolecular organization of the discotic molecule, hexakis(hexylthio)diquinoxalino[2,3-a:2',3'-c]phenazine, deposited on graphite. The ARUPS data reveal significant changes in the electronic properties when going from disordered to columnar phases, the main feature being a decrease in ionization potential by 1.8 eV following the appearance of new electronic states at low binding energy. This evolution is rationalized by quantum-chemical calculations performed on model stacks containing from two to six molecules, which illustrate the formation of a quasi-band structure with Bloch-like orbitals delocalized over several molecules in the column. The ARUPS data also point to an energy dispersion of the upper pi-bands in the columns by some 1.1 eV, therefore highlighting the strongly delocalized nature of the pi-electrons along the discotic stacks. |
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