One- and two-photon photoemission spectra have been measured for monolayers of oligo(para-phenylene-ethynylene) thiolate chemisorbed on gold surfaces. Within 5 eV of the Fermi level, four states are observed, two occupied (2.0 eV and 4.0 eV below the Fermi level) and two unoccupied (2.5 eV and 5.3 eV). The two states closest the Fermi level are assigned to conjugated states along the backbone of the molecule, and the other two are assigned to electronic conjugated states formed the ortho carbons. From this assignment, the charge-transport gap energy is estimated to be between 3.7 eV and 5.4 eV.
Citation: Journal of the American Chemical Society
Issue: No. 11
Pub Type: Journals
OPE, photoemission, SAM, self-assembly, valence levels