An experimental study of the bonding geometry and electronic coupling of cis-bis(isothiocyanato)bis(2,2(')-bipyridyl-4,4(')-dicarboxylato)-ruthenium(II) (N3) adsorbed on rutile TiO(2)(110) is presented, along with supporting theoretical calculations of the bonding geometry. Samples were prepared in situ using ultrahigh vacuum electrospray deposition. Core-level photoemission spectroscopy was used to characterize the system and to deduce the nature of the molecule-surface bonding. Valence band photoemission and N 1s x-ray absorption spectra were aligned in a common binding energy scale to enable a quantitative analysis of the bandgap region. A consideration of the energetics in relation to optical absorption is used to identify the photoexcitation channel between the highest occupied and lowest unoccupied molecular orbitals in this system, and also to quantify the relative binding energies of core and valence excitons. The core-hole clock implementation of resonant photoemission spectroscopy is used to reveal that electron delocalization from N3 occurs within 16 fs.

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The “core-hole clock” implementation of resonant photoemission has been used to investigate the charge-transfer dynamics of bi-isonicotinic acid molecules (4,4‘-dicarboxy-2,2‘-bipyridine) adsorbed on a rutile TiO2(110) surface containing varying densities of gold islands. In the presence of, nominally, a few monolayers of gold there exists a strong coupling between the adsorbed molecules and the surface. This is derived from the measurement of a <3 fs charge-transfer time for the injection of a core-excited electron into the substrate. This ultrafast charge-transfer time is quenched for a fraction of the molecules upon the addition of only a few further monolayers of gold. There is evidence to suggest that this effect derives from a change in the bonding configuration of bi-isonicotinic acid molecules. However, results also support the occurrence of ultrafast back-transfer from Au states to core-excited unoccupied molecular states.

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