AVS 52nd International Symposium
    Electronic Materials and Processing Thursday Sessions
       Session EM1-ThA

Paper EM1-ThA9
Photoelectron Spectroscopy of Phenylene Ethynylene versus Phenylene Vinylene Oligomers: a Search for Bond Alternation Effects

Thursday, November 3, 2005, 4:40 pm, Room 309

Session: Organic and Molecular Optoelectronics
Presenter: L.B. Picraux, NIST
Authors: L.B. Picraux, NIST
C.D. Zangmeister, NIST
S.W. Robey, NIST
R.D. van Zee, NIST
Correspondent: Click to Email
Interest in factors controlling transport through conjugated molecular systems has lead to a significant experimental effort investigating conductivity in various configurations of metal-molecule junctions. One interesting result of these efforts was an investigation of the relative conductivity in junctions formed using crossed wire techniques containing phenylene ethynylene (OPE) or phenylene vinylene (OPV) oligomers. Vinylene-based oligomers were found to exhibit higher conductivity, a result that was attributed to an increased bandgap in phenylene ethynylene systems due to the larger impact of bond alternation effects in the triple bond containing system. We have used photoelectron spectroscopy to investigate the @pi@ electronic structure of these two systems, namely three-ring phenylene ethynylene oligomers with thiol bound to gold and the analogous three-ring OPV system, which were the compounds employed in the crossed-wire investigations. Spectra for the two oligomers are quite similar but the @pi@ levels in the OPV variant are approximately 0.2 eV closer to the Fermi level than in OPE, possibly consistent with the higher conductivity measured in crossed-wire junctions.@footnote 1@ While this could be construed as being consistent with a narrowing of the band gap in the OPV system, it appears to arise from a rigid shift of the levels. There is no evidence of increased dispersion within the @pi@ manifold as expected if reduced bond alternation were the cause. Finally, we will also discuss the potential impact of the self-assembled monolayer structure on transport measurements. @FootnoteText@@footnote 1@Kushmerick JG, Hold DB, Pollack SK, et al., J. Am. Chem. Soc. 124(36): 10654-10655 2002.