title: Electronic delocalization in discotic liquid crystals: a joint experimental and theoretical study.
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.
authors.affiliation: Department of Physics and Measurement Technology, IFM, Linköping University, S-58183 Linköping, Sweden. xavcr@itn.liu.se
authors.forename: Xavier
authors.initials: X
authors.lastname: Crispin
authors.forename: Jérôme
authors.initials: J
authors.lastname: Cornil
authors.forename: Rainer
authors.initials: R
authors.lastname: Friedlein
authors.forename: Koji Kamiya
authors.initials: KK
authors.lastname: Okudaira
authors.forename: Vincent
authors.initials: V
authors.lastname: Lemaur
authors.forename: Annica
authors.initials: A
authors.lastname: Crispin
authors.forename: Gaël
authors.initials: G
authors.lastname: Kestemont
authors.forename: Matthias
authors.initials: M
authors.lastname: Lehmann
authors.forename: Mats
authors.initials: M
authors.lastname: Fahlman
authors.forename: Roberto
authors.initials: R
authors.lastname: Lazzaroni
authors.forename: Yves
authors.initials: Y
authors.lastname: Geerts
authors.forename: Göran
authors.initials: G
authors.lastname: Wendin
authors.forename: Nobuo
authors.initials: N
authors.lastname: Ueno
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Brédas
authors.forename: William R
authors.initials: WR
authors.lastname: Salaneck