Self-assembled monolayers (SAMs) of nitrile-substituted oligo(phenylene ethynylene) thiols (NC-OPEn) with a variable chain\r\nlength n (n ranging from one to three structural units) on Au(111) were studied by synchrotron-based high-resolution X-ray photoelectron\r\nspectroscopy and near-edge absorption fine-structure spectroscopy. The experimental data suggest that the NC-OPEn\r\nmolecules form well-defined SAMs on Au(111), with all the molecules bound to the substrate through the goldââ?¬â??thiolate anchor and\r\nthe nitrile tail groups located at the SAMââ?¬â??ambient interface. The packing density in these SAMs was found to be close to that of\r\nalkanethiolate monolayers on Au(111), independent of the chain length. Similar behavior was found for the molecular inclination,\r\nwith an average tilt angle of ~33ââ?¬â??36Ã?° for all the target systems. In contrast, the average twist of the OPEn backbone (planar conformation)\r\nwas found to depend on the molecular length, being close to 45Ã?° for the films comprising the short OPE chains and\r\n~53.5Ã?° for the long chains. Analysis of the data suggests that the attachment of the nitrile moiety, which served as a spectroscopic\r\nmarker group, to the OPEn backbone did not significantly affect the molecular orientation in the SAMs.
Loading....