In this Communication, the preparation conditions of the molecular films were described incorrectly. During the deposition of [Fe(bpz) 2 phen], the Au(111) substrate temperature was kept at about 100 8C. This correction does not affect the conclusions of the original Communication.

Submono-, mono- and multilayers of the Fe(II) spin-crossover (SCO) complex [Fe(bpz)2 (phen)] (bpz=dihydrobis(pyrazolyl)borate, phen=1,10-phenanthroline) have beenprepared by vacuum deposition on Au(111) substrates and investigated with near edge X-ray absorption fine structure (NEXAFS) spectroscopy and scanning tunneling microscopy (STM). As evidenced by NEXAFS, molecules of the second layer exhibit a thermal spin crossover transition, although with a more gradual characteristics than in the bulk. For mono- and submonolayers of [Fe(bpz)2 (phen)] deposited on Au(111) substrates at room temperature both NEXAFS and STM indicate a dissociation of [Fe(bpz)2 (phen)] on Au(111) into four-coordinate complexes, [Fe(bpz)2 ], and phen molecules. Keeping the gold substrate at elevated temperatures ordered monolayers of intact molecules of [Fe(bpz)2 (phen)] are formed which can be spin-switched by electron-induced excited spin-state trapping (ELIESST).

Electronic self-decoupling of an organic chromophore from a metal substrate is achieved using a naphtalenediimide cyclophane to spatially separate one chromophore unit of the cyclophane from the substrate. Observations of vibronic excitations in scanning tunneling spectra demonstrate the success of this approach. These excitations contribute a significant part of the tunneling current and give rise to clear structure in scanning tunneling microscope images. We suggest that this approach may be extended to implement molecular functions at metal surfaces.electron transport | functional molecules at surfaces | scanning tunneling microscopy | vibronic states P redictions are difficult, especially about the future. We hope that this truism will be valid for the future of surface science, too. Nevertheless, it appears to be safe to predict that functional molecules at surfaces will be one of the foci of surface science over the next decade. The opportunities in this field are virtually unlimited and range from technological issues such as controlling interface effects in organic devices to adventurous endeavors such as building molecular machines at surfaces. Although these topics are most challenging, the present state of the experimental and theoretical methods of surface science is good reason for optimism that significant scientific progress will be made in this field.This article focuses on the electronic coupling between molecules and a metal substrate. At the interface, charge transfer and hybridization affect the levels of an adsorbed molecule, which may significantly modify its properties. To recover and use the intrinsic molecular properties, which may be taylored over a wide range, a degree of decoupling from the metallic surface may be desirable. Effective molecular decoupling has been achieved using multilayers of molecules (1) or ultrathin insulating layers (2-5). An alternative approach is to chemically modify a molecule using spacer groups in order to lift a particular subunit from the substrate. With this aim, for instance, bulky groups have been used to preserve switching capability of an azobenzene derivative (6-11). Previously, this approach was used to obtain an electrical insulation of a model molecular wire (12). However, these molecules turned out to be too flexible and thus deformed upon adsorption at metal substrates (13).Here we use designed cyclophanes to achieve decoupling of one chromophore from a metal surface. These cyclophanes consist of two rigidly separated parallel π-systems from which only one adsorbs to the surface, whereas the second one is expected to remain separated from the metal. Thus, cyclophanes represent a class of molecules that are particularly interesting for investigating columnar π-stacking and through-space or through-bond electronic conductance (14-16). A naphthalenediimide (NDI) cyclophane (Fig. 1) was chosen as a model compound for the present study. It is demonstrated that this organic molecule, with its height of a few angstroms on a metallic substrate, provide...

Quantum-dot Cellular Automata (QCA) exploit quantum confinement, tunneling and electrostatic interaction for transistorless digital computing. Implementation at the molecular scale requires carefully tailored units which must obey several structural and functional constraints, ranging from the capability to confine charge efficiently on different 'quantum-dot centers'-in order to sharply encode the Boolean states-up to the possibility of having their state blanked out upon application of an external signal. In addition, the molecular units must preserve their geometry in the solid state, to interact electrostatically in a controlled way. Here, we present a novel class of organometallic molecules, 6-3,6-bis(1-ethylferrocen)-9H-carbazol-9-yl-6-hexan-1-thiols, which are engineered to satisfy all such crucial requirements at once, as confirmed by electrochemistry and scanning tunneling microscopy measurements, and first principles density functional calculations.

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A scanning tunneling microscope is used to induce the emission of light from a monolayer of naphtalenediimide cyclophane, a molecule comprising two separate π -electron systems. Spectra of the emission exhibit clear features related to vibrational molecular states. They are interpreted in terms of the unusual density of unoccupied states of the molecule, which causes a drastic preference of inelastic tunneling to the molecular affinity level.

Self-assembled monolayers (SAMs) of cobalt(II) 5,10,15,20-tetrakis(4-tert-butylphenyl)-porphyrin, a promising material for optical, photoelectrochemical, and chemical sensor applications, were prepared on Au(111) via axial ligation to 4-aminothiophenol, and studied by several surface science techniques. Scanning tunneling microscopy (STM) and spectroscopy (STS) measurements showed the apparent topology of the Au(111) herringbone structure reconstruction, but with bias-dependent contrast images and asymmetric I/V characteristics. Photoelectron spectroscopy confirmed the presence of metalloporphyrins on the surface, whereas near-edge X-ray absorption (NEXAFS) measurements revealed that the porphyrin ring was tilted by about 70 degrees with respect to the surface plane. The above effects are ascribed to the presence of oriented molecular dipole layers between the metal and the organic material as confirmed by a comparison with first-principles density-functional theory calculations. The measured bias-dependent STM profiles have been reproduced by a simple monodimensional tunneling model.

A new azopyridine functionalized Ni-porphyrin was synthesized as a model compound for deposition and switch on surfaces. Two geometrically and electronically different states of single molecules on Au(111) were found by scanning tunneling microscopy/ spectroscopy and analyzed with density functional calculations.Switching is an elementary step in many sophisticated functions, such as directed motion, pumping, information storage and processing, in the macroscopic world as well as at the molecular scale.1 For nanoscale applications of such functions, molecules have to be immobilized on solid supports in a well defined geometry and orientation, in order to achieve advanced and reproducible dynamic functions. Moreover, a controlled electronic coupling with the surface as well as sufficient space for molecular movement during an isomerization process are required to avoid charge transfer and hybridization with the surface or intermolecular interactions.2 Immobilization and decoupling have been achieved by anchoring functional molecules with a thiol group and an alkane spacer on gold surfaces.3 Sterical hindrance within a densely packed selfassembled monolayer can be avoided by dilution of the functional molecules using short alkane thiols. 4 However, usually stochastic rather than ordered monolayers are obtained. To achieve decoupling from the surface, bulky tert-butyl substituents were attached to a molecular framework to lift it away from the surface. 5,6 Vertical alignment at a large distance from the surface and control over the distance of the functional groups with respect to each other were attempted by constructing molecular tripods with thiol feet.7 Anyway, ordered monolayers are difficult to obtain and it has been shown that not all feet touch the gold surface.7i Modular platforms and spacers have been recently introduced to control distance from the surface, orientation and packing density. 8 In view of the construction of controllable functional surfaces, further chemical methodologies for a rational vertical design of complex surface architectures are needed.To combine the cis-trans switching capability of azopyridine with the property of porphyrins to form ordered self-assembled monolayers we covalently attached a 3-azopyridine unit to a Ni(II) tetraphenylporphyrin (Ni-TPP). The porphyrin platform provides bonding to the surface, electronic decoupling and a fixed orientation of the azopyridine unit. Azobenzene functionalized porphyrins have been synthesized previously. However, the azo group was attached in the para position to the meso phenyl substituents, thus lying within the porphyrin molecular plane. 9 We attached an azopyridine unit in the ortho position to one of the meso phenyl groups of tetraphenylporphyrin, thus allowing the azopyridine to protrude from the surface. Direct synthesis from a mixture of pyrrole, benzaldehyde, and an azopyridine functionalized benzaldehyde in a 4 : 3 : 1 ratio failed. Using prefabricated dipyrromethane units for cyclization furnished the monosubstituted tetraph...