Comparison between angular dependent NEXAFS analysis and theoretical calculations of molecular orientation of new functional mixed aromatic molecules deposited onto Au/Si(111)

Self-assembled mixed component aromatic layers oil gold, prepared from solutions of 4'(4-mercaptophenyl)-2,2':6',2"-terpyridine (MPTP) and mercaptobenzene (MB), have been investigated by means of angular dependent NEXAFS spectroscopy at the C K-edge and N K-edge. For such a system, angular dependent NEXAFS data analysis provides information on the molecular arrangement ill excellent agreement with theoretical calculations. The presence of mercaptobenzene molecule forces the terpyridine-containing molecule to an organized molecular arrangement. Analysis of the angular dependence of a few selected resonances of both the C K-edge and N Kedge spectra, i.e. the pi* C=C, the pi* C=N and the pi* N-C, for the mixed layer (MPTP/MB) and for the terpyridine (MPTP), allowed to establish that in the mixed conditions the three external pyridine rings are arranged in a geometry in which they stand up respect to the Au surface and they are nearly coplanar to each other, in a completely similar fashion to the MPTP sample itself. The presence of MB in the mixed system induces a tilting up of the phenyl ring of MPTP, as evidenced by the calculations, but seems to leave virtually unaffected the arrangement of the three external pyridine rings. (c) 2005 Elsevier B.V. All rights reserved.