Electronic and Geometric Structure of Bimetallic Clusters: Density Functional Calculations on [M(4){Fe(CO)(4)}(4)](4-) (M = Cu, Ag, Au) and [Ag(13){Fe(CO)(4)}(8)](n)(-) (n = 0-5)

The results of all-electron density functional calculations on the bimetallic cluster compounds [M(4){Fe(CO)(4)}(4)](4-) (M = Cu, Ag, Au) and on the corresponding naked species M(4)Fe(4) are reported. The trends within the triad have been investigated. The bare metal clusters exhibit a strong magnetization which is quenched on addition of CO ligands. The bonding in the bare clusters is different for the silver derivative compared to that of copper and gold, resulting in comparatively weaker Ag-Fe and Ag-Ag bonds. This can be rationalized in terms of the different d-sp mixing, which for Cu and Au is larger than for Ag. Relativistic effects act to increase the 4d-5s mixing in Ag and to strengthen the intermetallic bond with Fe. In the carbonylated clusters a charge transfer from the metal M (M = Cu, Ag, or Au) to the Fe(CO)(4) groups occurs so that the atoms M can be considered in a formal +I oxidation state, rationalizing the nearly square-planar geometry of the metal frame. In fact, the local coordination of the M atoms is almost linear, as expected for complexes of M(I). The addition of extra electrons results in a stabilization of the clusters, indicating the electron-deficient nature of these compounds. Similar features have been found for the largest cluster synthesized so far for this class of compounds, [Ag(13){Fe(CO)(4)}(8)](n)(-), (n = 0-5). The nature and localization of the unpaired electron in the tetraanion is also discussed.     

Syntheses, characterization, and luminescence of Pt II-M I (M = Cu, Ag, Au) heterometallic complexes by incorporating Pt(diimine)(dithiolate) with [M2(dppm)2]2+ (dppm = Bis(diphenylphosphino)methane)

Reaction of Pt(diimine)(edt) (edt = 1,2-ethanedithiolate) with M(2)(dppm)(2)(MeCN)(2)(2+) (dppm = bis(diphenylphosphino)methane) gave heterotrinuclear complexes [PtCu(2)(edt)(mu-SH)(dppm)(3)](ClO(4)) (11) and [PtCu(2)(diimine)(2)(edt)(dppm)(2)](ClO(4))(2) (diimine = 2,2'-bpyridine (bpy), 12; 4,4'-dibutyl-2,2'-bipyridine (dbbpy), 13; phenanthroline (phen), 14; 5-bromophenanthroline (brphen), 15) when M = Cu(I). The reaction, however, afforded tetra- and trinuclear complexes [Pt(2)Ag(2)(edt)(2)(dppm)(2)](SbF(6))(2) (17) and [PtAu(2)(edt)(dppm)(2)](SbF(6))(2) (21) when M = Ag(I) and Au(I), respectively. The complexes were characterized by elemental analyses, electrospray mass spectroscopy, (1)H and (31)P NMR, IR, and UV-vis spectrometry, and X-ray crystallography for 14, 17, and 18. The Pt(II)Cu(I)(2) heterotrinuclear complexes 11-15 exhibit photoluminescence in the solid states at 298 K and in the frozen acetonitrile glasses at 77 K. It is likely that the emission originates from a ligand-to-metal charge transfer (dithiolate-to-Pt) (3)[p(S) --> d(Pt)] transition for 11 and from an admixture of (3)[d(Cu)/p(S)-pi(diimine)] transitions for 12-16. The Pt(II)(2)Ag(I)(2) heterotetranuclear complexes 17 and 18 are nonemissive in the solid states and in solutions at 298 K but show photoluminescence at 77 K. The Pt(II)Au(I)(2) heterotrinuclear complexes 19-21, however, are luminescent at room temperature in the solid state and in solution. Compounds 19 and 20 afford negative solvatochromism associated with a charge transfer from an orbital of a mixed metal/dithiolate character to a diimine pi orbital.     

Binding at molecule/gold transport interfaces. V. Comparison of different metals and molecular bridges

The geometric and electronic structural properties of symmetric and asymmetric metal cluster-molecule-cluster' complexes have been explored. The metals include Au, Ag, Pd, and Al, and both benzenedithiol and the three isometric forms of dicyanobenzene are included as bridging molecules. Calculated properties such as cluster-molecule interface geometry, electronic state, degree of metal --> molecule charge transfer, metal-molecule mixing in the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy region, the HOMO-LUMO gap, cluster --> cluster' charge transfer as a function of external field strength and direction, and the form of the potential profile across such complexes have been examined. Attempts are made to correlate charge transport with the characteristics of the cluster-complex systems. Indications of rectification in complexes that are asymmetric in the molecule, clusters, and molecule-cluster interfaces are discussed. The results obtained here are only suggestive because of the limitations of the cluster-complex model as it relates to charge transport.     

Ultraviolet photoelectron spectroscopic study on the interface electronic structure of the L-cysteine on Pd surface

L-cysteine is one of the most versatile biomolecules with a unique metal-binding ability. L-cysteine has an outstanding role in the bioelectronics field as a linker between proteins of biomolecules and metal electrodes of the inorganic metals through multiple functional groups. The interface electronic structures between L-cysteine with metals deserve further investigation for applications in bioelectronics. However, the interface electronic structures of L-cysteine and metals have not been well understood. We have previously reported the existence of a new state between the highest occupied molecular orbital (HOMO) of L-cysteine and the Fermi level of the metals for L-cysteine/Au(111), L-cysteine/Ag(111), and L-cysteine/Cu(111) using photoemission spectroscopy and attributed the formation of the new state to an interaction of the d band with HOMO of L-cysteine. In this study, the electronic structure at the interfaces of L-cysteine on a Palladium (Pd) surface is investigated by ultraviolet photoemission spectroscopy (UPS) using synchrotron radiation including work function, secondary electron cutoff (SECO), and HOMO onset; the position of an interface state, charge injection barrier, and ionization energy are estimated. It is observed that thin-film spectra of L-cysteine on Pd surfaces in the valance top region are different from the L-cysteine thick films, and this can be attributed to an interaction between a sulfur-originated state of L-cysteine HOMO with Pd d orbitals. Also, a 0.6-eV SECO shift is estimated due to the charge transferring between L-cysteine and Pd. The results of SECO further confirm the weakening of the Pd–sulfur bond with increasing L-cysteine coverage on Pd.     

Luminescent heteronuclear Au(I)5Ag(I)8 complexes of [1,2,3-C6(C6H4R-4)3]3- (R = H, CH3, But) by cyclotrimerization of arylacetylides

Unusual AuI-AgI heterometallic complexes [Au5Ag8(mu-dppm)4{1,2,3-C6(C6H4R-4)3}(CCC6H4R-4)7]3+ (R = H 1, CH3 2, But 3) were isolated by reactions of polymeric silver arylacetylides (AgCCC6H4R-4)n with binuclear gold component [Au2(mu-dppm)2(MeCN)2]2+ (dppm = bis(diphenylphosphino)methane), in which cyclotrimerization of arylacetylide -CCC6H4R-4 affords trianion {1,2,3-C6(C6H4R-4)3}3- with an unprecedented mu5-bonding mode. Compounds 1(SbF6)3-3(SbF6)3 exhibit intense photoluminescence derived from an MLCT (Au5Ag8 --> CCC6H4R-4) transition, mixed with a metal cluster-centered excited states.     

Ordered phthalocyanine superstructures on Ag(110)

Organic-metal interfaces, in particular, self-assembling systems, are interesting in the field of molecular electronics. In this study, we have investigated the formation of the Ag(110)-iron phthalocyanine (FePc) interface in a coverage range of less than 1 and up to 2 ML using synchrotron based photoelectron spectroscopy and low energy electron diffraction. As-deposited FePc forms a densely packed first layer exhibiting a 3 x 2c(6 x 2) symmetry. Upon thermal treatment the order at the interface is modified depending on the initial FePc coverage, resulting in less densely packed but still ordered superstructures. The first monolayer is relatively strongly bound to the substrate, leading to the formation of an interface state just below the Fermi level. The highest occupied molecular orbital of FePc in the second layer is found at 1 eV higher binding energy compared to the interface state.     

Molecular layers of ZnPc and FePc on Au(111) surface: Charge transfer and chemical interaction

We have studied zinc phthalocyanine (ZnPc) and iron phthalocyanine (FePc) thick films and monolayers on Au(111) using photoelectron spectroscopy and x-ray absorption spectroscopy. Both molecules are adsorbed flat on the surface at monolayer. ZnPc keeps this orientation in all investigated coverages, whereas FePc molecules stand up in the thick film. The stronger inter-molecular interaction of FePc molecules leads to change of orientation, as well as higher conductivity in FePc layer in comparison with ZnPc, which is reflected in thickness-dependent differences in core-level shifts. Work function changes indicate that both molecules donate charge to Au; through the π-system. However, the Fe3d derived lowest unoccupied molecular orbital receives charge from the substrate when forming an interface state at the Fermi level. Thus, the central atom plays an important role in mediating the charge, but the charge transfer as a whole is a balance between the two different charge transfer channels; π-system and the central atom.     

C6H6/Au(111): interface dipoles, band alignment, charging energy, and van der Waals interaction

We analyze the benzene/Au(111) interface taking into account charging energy effects to properly describe the electronic structure of the interface and van der Waals interactions to obtain the adsorption energy and geometry. We also analyze the interface dipoles and discuss the barrier formation as a function of the metal work-function. We interpret our DFT calculations within the induced density of interface states (IDIS) model. Our results compare well with experimental and other theoretical results, showing that the dipole formation of these interfaces is due to the charge transfer between the metal and benzene, as described in the IDIS model.     

Relativistic-consistent electron densities of the coinage metal clusters M2, M4, M4(2-), and M4Na2 (M = Cu, Ag, Au): a QTAIM study

We employ second-order M?ller-Plesset perturbation theory level in combination with recently developed pseudopotential-based correlation consistent basis sets to obtain accurate relativistic-consistent electron densities for small coinage metal clusters. Using calculated electron densities, we employ Bader's quantum theory of atoms in molecules (QTAIM) to gain insights into the nature of metal-metal bonding in the clusters M(2), M(4), M(4)(2-), and M(4)Na(2) (M = Cu, Ag, Au). For the simplest case of the metal dimer, M(2), we correlate the strength of the metal-metal bond with the value of the electron density at the bond critical point, the total energy density at the bond critical point, the sharing (delocalization) index, and the values of the two principle negative curvatures. We then consider changes to the metal-metal bonding and charge density distribution upon the addition of two metal atoms to form the metal tetramer, M(4), and then followed by the addition of an electron pair to form M(4)(2-) and finally followed by the addition of two alkali metal (sodium) ions to form M(4)Na(2). Using topological properties of the electron density, we present evidence for the existence of σ-aromaticity in Au(4)(2-). We also report the existence of two non-nuclear attractors in the molecular graph of Cu(4)(2-) and large negative charge accumulation in the nonbonded Cu basins of this cluster.     

Silver Makes Better Electrical Contacts to Thiol‐Terminated Silanes than Gold

We report that the single‐molecule junction conductance of thiol‐terminated silanes with Ag electrodes are higher than the conductance of those formed with Au electrodes. These results are in contrast to the trends in the metal work function Φ(Ag)<Φ(Au). As such, a better alignment of the Au Fermi level to the molecular orbital of silane that mediates charge transport would be expected. This conductance trend is reversed when we replace the thiols with amines, highlighting the impact of metal–S covalent and metal–NH₂ dative bonds in controlling the molecular conductance. Density functional theory calculations elucidate the crucial role of the chemical linkers in determining the level alignment when molecules are attached to different metal contacts. We also demonstrate that conductance of thiol‐terminated silanes with Pt electrodes is lower than the ones formed with Au and Ag electrodes, again in contrast to the trends in the metal work‐functions.     

双核Au(Ⅰ)配合物[Y+]2[Au(i-mnt)]2(Y+=[n-Bu4N]+,K+,[Ph4As]+)发光机制的从头计算研究

用从头算方法研究[Au(i-mnt)]22-(i-mnt=i-marononitriledithiolate)的电子吸收和磷光发射性质,利用MP2和CIS方法分别优化了[Au(i-mnt)]22-基态和激发态几何结构.计算的基态Au(Ⅰ)—Au(Ⅰ)键长为0.2825nm,表明Au(Ⅰ)之间存在弱吸引作用.采用SCRF方法中IPCM模型模拟配合物在乙氰溶液中的行为,计算得到的最大吸收波长为315.5nm,指认X1Ag→A1Au来源于i-mnt配体内电荷转移跃迁.在436.2nm处得到具有B3Au→1Ag跃迁的磷光发射,指认为i-mnt配体内电荷转移和金属到配体电荷转移跃迁,与500nm乙氰溶液的发射相对应,为金属修饰的有机配体发光机制.     

AeMg(5)In(3) (Ae = Ba, Sr): new intermetallic compounds with well-differentiated roles for the normal cation types

The isostructural phases BaMg4.787(3)In3.213 and SrMg4.837(2)In3.163 were synthesized via high-temperature reactions of the elements in welded Ta tubes. The orthorhombic crystal structure established for these by single-crystal X-ray diffraction means (space group Pnma, Z = 4) features a 3D Mg-In network formed from condensed 21-vertex polyhedra that are centered by Ba (Sr), viz., Ae@Mg5M7In9 (M = Mg/In). Three of eight independent network sites are co-occupied by >90% Mg and <10% In(M). The network structure is the inverse of that found in the isopointal Ca(CaIn4)Au3, as clearly delineated by site charge estimates for the equivalent In3 versus Au3 positions. Tight-binding LMTO and extended Hückel calculations on the ordered AeMg5In3 support the differentiation of Mg and Ae in the structure, with substantial participation of Mg in dominant Mg-In bonding, but mainly an electron donor role for Ae. The Fermi energies lie close to pseudo gaps but with substantial DOS remaining, consistent with their measured metallic properties. An unmixed ideal AeMg5In3 would be isostructural with YCo5P3, with comparable polyhedra, but the small P in the latter lacks an effective interbridging role.     

A combined experimental and theoretical study on the effect of doping and interface formation on Ppv-ether copolymer

We present a detailed optoelectronic and vibrational study devoted to the transformation from neutral to doped PPV-ether copolymer in both powder and thin film states. The full geometries were optimized with the density functional theory (DFT) for neutral and doped states, where a comparative geometric study was established. The lowest singlet excited-state geometries have been investigated by using the configuration interaction single (CIS/3-21G(d)) method. The absorption spectra are then calculated respectively on the basis of the ground- and excited-state geometries. Our calculation results are in close agreement with those available from experiments. The charge distribution and excitation energies of singly charged PPV-ether are calculated, where two subgap absorption features are found to dominate the optical spectrum correlated with the polaron picture. These theoretical results are compared to experimental optical data illustrated by iodine-doped PPV-ether. Next, we have performed a simulation to model the conformations and the electronic structure modifications of interface formation of PPV-ether copolymer thin film with calcium (Ca), magnesium (Mg), and aluminum (Al) metal as a cathode and indium tin oxide (ITO) as anode in polymer LEDs. By providing the optical parameter obtained and the chemical reaction at the interface, we present the energetic diagram near the interface and the energy position of the lowest occupied molecular orbital with respect to the electrode Fermi level.     

Heterovalent Au(III)-M(I) (M=Cu, Ag, Au) complexes derived from incorporation of [Au(tdt)2]- (tdt = toluene-3,4-dithiolate) with [M2(dppm)2]2+ (dppm = Bis(diphenylphosphino)methane)

Polynuclear heterovalent Au(III)-M(I) (M = Cu, Ag, Au) cluster complexes [Au(III)Cu(I)8(mu-dppm)3(tdt)5]+ (1), [Au(III)3Ag(I)8(mu-dppm)4(tdt)8]+ (2), and [Au(III)Au(I)4(mu-dppm)4(tdt)2]3+ (3) were prepared by reaction of [Au(III)(tdt)2]- (tdt = toluene-3,4-dithiolate) with 2 equiv of [M(I)2(dppm)2]2+ (dppm = bis(diphenylphosphino)methane). Complex 3 originates from incorporation of one [Au(III)(tdt)2]- with two [Au(I)2(dppm)2]2+ components through Au(III)-S-Au(I) linkages. Formation of complexes 1 and 2, however, involves rupture of metal-ligand bonds in the metal components and recombination between the ligands and the metal atoms. The Au(tdt)2 component connects to four M(I) atoms through Au(III)-S-M(I) linkages in syn and anti conformations in complexes 1 (M = Cu) and 3 (M = Au), respectively, but in both syn and anti conformations in complex 2 (M = Ag). The tdt ligand exhibits five types of bonding modes in complexes 1-3, chelating Au(III) or M(I) atoms as well as bridging Au(III)-M(I) or M(I)-M(I) atoms in different orientations. Although complexes 1 and 2 are nonemissive, Au(III)Au(I)(4) complex 3 shows room-temperature luminescence with emission maximum at 555 nm (tau(em) = 3.1 micros) in the solid state and at 570 nm (tau(em) = 1.5 micros) in acetonitrile solution.     

Luminescent gold(I) and silver(I) complexes of 2-(diphenylphosphino)-1-methylimidazole (dpim): characterization of a three-coordinate Au(I)-Ag(I) dimer with a short metal-metal separation

The Au(I) and Ag(I) closed-shell metal dimers of 2-(diphenylphosphino)-1-methylimidazole, dpim, were investigated. dpim formed the discreet binuclear species [Ag2(dpim)2(CH3CN)2](2+) (1) when reacted with appropriate Ag(I) salts. Likewise, [Au2(dpim)2](2+) (3) and [AuAg(dpim)3](2+) (4) were produced via reactions with (tht)AuCl, tht is tetrahydrothiophene, and Ag(I). Compound 3 exhibits an intense blue luminescence (lambdamax=483 nm) in the solid state. However, upon initial formation of 3, a small impurity of Cl- was present giving rise to an orange emission (lambdamax=548 nm). Attempts to form [Au2(dpim)2]Cl2 yielded only (dpim)AuCl (2), which is not visibly emissive. The rare three-coordinate heterobimetallic complex [AuAg(dpim)3](2+) (4) exhibits intense luminescence in the solid-state resembling that of 3. The crystal structures of 1-4 were determined, revealing strong intramolecular aurophilic and argentophilic interactions in the dimeric compounds. Compound 1 has an Ag(I)-Ag(I) separation of 2.9932(9) A, while compound 3 has a Au(I)-Au(I) separation of 2.8174(10) A. Compound 4 represents the first example of a three-coordinate Au(I)-Ag(I) dimer and has a metal-metal separation of 2.8635(15) A. The linear Au(I) monomer, 2, has no intermolecular Au(I)-Au(I) interactions, with the closest separation greater than 6.8 A.     

Structural, photophysical, and catalytic properties of Au(I) complexes with 4-substituted pyridines

Ionic gold(I) complexes with general formula of [Au(Py)2][AuCl2] and [Au(Py)2][PF6] (Py = 4-substituted pyridines) have been synthesized. Structures of five Au(I) complexes and a Ag(I) complex were determined by single crystal X-ray diffraction. Evidence for cationic aggregation of [Au(py)2][PF6] complexes in solution was obtained by conductivity measurements and by the isosbestic point observed from variable temperature UV-visible absorption spectra. All compounds were luminous in the solid state. Calculations employing density functional theory were performed to shed light on the nature of the electronic transitions. While the [Au(4-dmapy)2][AuCl2] (4-dmapy = 4-dimethylaminopyridine) and [Au(4-pic)2][AuCl2] (4-pic = 4-picoline) emissions were found to be mainly ligand in nature, their [PF6](-) counterparts involved a Au...Au-interaction imbedded in the highest occupied molecular orbital. [Au(4-dmapy)2][AuCl2] was found to be an efficient catalyst for Suzuki cross-coupling of aryl bromide and phenylboronic acid.     

Excited-state interactions for [Au(CN)(2)(-)](n) and [Ag(CN)(2)(-)](n) oligomers in solution. Formation of luminescent gold-gold bonded excimers and exciplexes.

Solutions of K[Au(CN)(2)] and K[Ag(CN)(2)] in water and methanol exhibit strong photoluminescence. Aqueous solutions of K[Au(CN)(2)] at ambient temperature exhibit luminescence at concentration levels of > or =10(-2) M, while frozen methanol glasses (77 K) exhibit strong luminescence with concentrations as low as 10(-5) M. The corresponding concentration limits for K[Ag(CN)(2)] solutions are 10(-1) M at ambient temperature and 10(-4) M at 77 K. Systematic variations in concentration, solvent, temperature, and excitation wavelength tune the luminescence energy of both K[Au(CN)(2)] and K[Ag(CN)(2)] solutions by >15 x 10(3) cm(-1) in the UV-visible region. The luminescence bands have been individually assigned to *[Au(CN)(2)(-)](n) and *[Ag(CN)(2)(-)](n) excimers and exciplexes that differ in "n" and geometry. The luminescence of Au(I) compounds is related for the first time to Au-Au bonded excimers and exciplexes similar to those reported earlier for Ag(I) compounds. Fully optimized unrestricted open-shell MP2 calculations for the lowest-energy triplet excited state of staggered [Au(CN)(2)(-)](2) show the formation of a Au-Au sigma single bond (2.66 A) in the triplet excimer, compared to a weaker ground-state aurophilic bond (2.96 A). The corresponding frequency calculations revealed Au-Au Raman-active stretching frequencies at 89.8 and 165.7 cm(-1) associated with the ground state and lowest triplet excited state, respectively. The experimental evidence of the exciplex assignment includes the extremely large Stokes shifts and the structureless feature of the luminescence bands, which suggest very distorted excited states. Extended Hückel (EH) calculations for [M(CN)(2)(-)](n) and *[M(CN)(2)(-)](n) models (M = Au, Ag; n = 2, 3) indicate the formation of M-M bonds in the first excited electronic states. From the average EH values for staggered dimers and trimers, the excited-state Au-Au and Ag-Ag bond energies are predicted to be 104 and 112 kJ/mol, respectively. The corresponding bond energies in the ground state are 32 and 25 kJ/mol, respectively.     

The influence of electron confinement,quantum size effects,and film morphology on the dispersion and the damping of plasmonic modes in Ag and Au thin films

Plasmons are collective longitudinal modes of charge fluctuation in metal samples excited by an external electric field. Surface plasmons (SPs) are waves that propagate along the surface of a conductor. SPs find applications in magneto-optic data storage, optics, microscopy, and catalysis.The investigation of SPs in silver and gold is relevant as these materials are extensively used in plasmonics. The theoretical approach for calculating plasmon modes in noble metals is complicated by the existence of localized d electrons near the Fermi level. Nevertheless, recent calculations based on linear response theory and time-dependent local density approximation adequately describe the dispersion and damping of SPs in noble metals.Furthermore, in thin films the electronic response is influenced by electron quantum confinement. Confined electrons modify the dynamical screening processes at the film/substrate interface by introducing novel properties with potential applications. The presence of quantum well states in the Ag and Au overlayer affects both the dispersion relation of SP frequency and the damping processes of the SP.Recent calculations indicate the emergence of acoustic surface plasmons (ASP) in Ag thin films exhibiting quantum well states. The slope of the dispersion of ASP decreases with film thickness.High-resolution electron energy loss spectroscopy (HREELS) is the main experimental technique for investigating collective electronic excitations, with adequate resolution in both the energy and momentum domains to investigate surface modes.Herein we review on recent progress of research on collective electronic excitations in Ag and Au films deposited on single-crystal substrates.     

Density functional theory study of the carbonyl-ene reaction of encapsulated formaldehyde in Cu(I), Ag(I), and Au(I) exchanged FAU zeolites

Carbonyl-ene reactions, which involve C-C bond formation, are essential in many chemical syntheses. The formaldehyde-propene reaction catalyzed by several of the group 11 metal cations, Cu(+), Ag(+), and Au(+) exchanged on the faujasite zeolite (metal-FAU) has been investigated by density functional theory at the M06-L/6-31G(d,p) level. The Au-FAU exhibits a higher activity than the others due to the high charge transfer between the Au and the reactant molecules, even though it is located at a negatively charged site of the zeolite. This site enables it to compensate for the charge of the Au(+) ion. The NBO analysis reveals that the 6s orbital of the Au atom plays an important role, inducing a charge on the probe molecules. Moreover, the effect of the zeolite framework makes the Au-FAU more active than the others by stabilizing the high charge induced transition structure. The activation energy of the reaction catalyzed by Au-FAU is 13.0 kcal/mol whereas that of Cu and Ag-FAU is found to be around 17 kcal/mol. The product desorption needs to be improved for Au-FAU; however, we suggest that catalysts with high charge transfer might provide a promising activity.     

Determination of the electronic structure of self-assembled L-cysteine/Au interfaces using photoemission spectroscopy

The electronic and chemical structure of the interface between the amino acid L-cysteine and Au was determined by photoemission spectroscopy (PES). L-cysteine was deposited by repeatedly dipping Au substrates into solutions of L-cysteine in methanol with various concentrations. To enable repeat deposition without significant contamination, the dipping procedure was performed in a glovebox directly connected to the ultrahigh vacuum (UHV) chamber in a N2 atmosphere. X-ray photoemission spectroscopy (XPS) measurements between deposition steps allowed to characterize the chemical interaction at the interface to be characterized. Ultraviolet photoemission spectroscopy (UPS) measurements yielded the orbital line-up at the interface as well as the highest occupied molecular orbital (HOMO) structure of L-cysteine. The charge injection barrier between the L-cysteine HOMO and the Au Fermi level was found to be 3.0 eV. The interface dipole between the Au substrate and the L-cysteine overlayer was determined to be 1.03 eV. The results also indicate the formation of an interface state approximately 1.5 eV above the HOMO of the L-cysteine.