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