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The growth of controlled 1D carbon-based nanostructures on metal surfaces is a multistep process whose path, activation energies and intermediate metastable states strongly depend on the employed substrate. Whereas this process has been extensively studied on gold, less work has been dedicated to silver surfaces, which have a rather different catalytic activity. In this work, we present an experimental and theoretical investigation of the growth of poly-$p$-phenylene (PPP) chains and subsequent narrow graphene ribbons starting from 4,4''-dibromo-$p$-terphenyl molecular precursors deposited at the silver surface. By combing scanning tunneling microscopy (STM) imaging and density functional theory (DFT) simulations, we describe the molecular morphology and organization at different steps of the growth process and we discuss the stability and conversion of the encountered species on the basis of calculated thermodynamic quantities. Unlike the case of gold, at the debromination step we observe the appearance of organometallic molecules and chains, which can be explained by their negative formation energy in the presence of a silver adatom reservoir. At the dehydrogenation temperature the persistence of intercalated Br atoms hinders the formation of well-structured graphene ribbons, which are instead observed on gold, leading only to a partial lateral coupling of the PPP chains. We numerically derive very different activation energies for Br desorption from the Ag and Au surfaces, thereby confirming the importance of this process in defining the kinetics of the formation of molecular chains and graphene ribbons on different metal surfaces.

Circular economy is considered a new chance to build a more sustainable world from both the social and the economic point of view. In this Essay, the possible contribution of inorganic chemistry towards a smooth transition to circularity in inorganic materials design and production is discussed by adopting an interdisciplinary approach.

The relative stability of trans-[(η5-C5H5)Fe(η1-CO)(μ-CO)]2 (trans-I) and cis-I tautomers in a vacuum and in solvents with different dielectric constants (e) has been investigated by exploiting density functional theory (DFT). Theoretical results indicate that, in agreement with experimental evidence, trans-I is more stable than cis-I in a vacuum (∼1.5 kcal mol−1; e = 1), while the opposite is true in media with e > 7. Differently from solution, DFT outcomes pertaining to the vapor-phase cis-I ⇆ trans-I equilibrium at T = 368 K, the temperature at which the Fe L2,3-edges and the C and O K-edge X-ray absorption spectroscopy (XAS) data of I have been recorded, ultimately indicate the trans-I predominance (∼93%). Compositions, oscillator strengths (f) and excitation energy (EE) values of cis-I transitions substantially mirror those of trans-I; nevertheless, the weighted cis-If(EE) distributions negligibly contribute to the diverse simulated XA spectra of I.

This work is focused on the structural control of graphene nanoribbons (GNRs) and intermediate polymeric wires [poly(p-phenylene), PPP] during their thermoactivated bottom-up synthesis from room te...

Electrolyte-Gated Organic Field-Effect Transistors (EGOFETs) offer many opportunities for the development of low-cost and low-power electronics suitable for applications like sensors and point-of-care tests; however, EGOFETs can be affected by the drift of their operative point that causes signals distortion and loss of information during sensing applications. Here, a blend of 2,8-Difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene (diF-TES-ADT) and polystyrene (PS) is used as the active material for the fabrication of dual-gate EGOFETs. We exploited the dual-gate architecture to improve EGOFETs stability by implementing digital feedback that uses the back-gate electrode to compensate dynamically for the transistor threshold voltage allowing us to fix its operative point for prolonged tests (>10 h) with different aqueous solutions (Milli-Q water, NaCl 0.1 M and a physiological solution). The presented real-time threshold voltage compensation does not only allow to steady EGOFETs DC output current, but it also preserves EGOFETs sensing capability for the detection of signals with frequencies as low as 1 Hz., The research leading to these results has received funding from the University of Padua, Department of Chemical Sciences (Grants: P-DISC#09BIRD2019-UNIPD - SMOW -; P-DiSC#11NExuS_BIRD2020-UNIPD - CARBON-FET -). It is further funded by the Italian Ministry of Education, Universities and Research through the project entitled “Nanochemistry for Energy and Health, NExuS” (the national funding network termed “Dipartimenti di Eccellenza” awarded to the Department of Chemical Sciences at the University of Padua). This work was partially supported by the University of Padua, Department of Information Engineering, under the initiative Project PROACTIVE 2018, and by MIUR (Italian Minister for Education) under the initiative “Departments of Excellence” (Law 232/2016). This work was funded by the Spanish Ministry of Science and Innovation with the project GENESIS PID2019-111682RB-I00 and through the “Severo Ochoa” Programme for Centers of Excellence in R&D (FUNFUTURE CEX2019-000917-S), and the Generalitat de Catalunya (2017-SGR-918). S. R. acknowledges her FPI fellowship and is enrolled in the UAB PhD program., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

The unoccupied electronic structures of three closed-shell, highly popular organoiron complexes ([Fe(CO)5], [(η5-C5H5)Fe(CO)(μ-CO)]2, and [(η5-C5H5)2Fe]; 0, I, and II, respectively) have been investigated both experimentally and theoretically by combining original gas-phase X-ray absorption spectroscopy (XAS) outcomes recorded at the C and O K-edge with results of scalar relativistic time-dependent density functional calculations carried out within the zeroth order regular approximation. Experimental evidence herein discussed complement the Fe L2,3-edges XAS ones we recently recorded, modeled, and assigned for the same complexes (Carlotto et al. Inorg. Chem. 2019, 58, 5844). The first-principle simulation of the C and O K-edge features allowed us to univocally identify the electronic states associated to the ligand-to-metal charge transfer (LMCT) transitions both in I and in II. At variance to that, LMCT transitions with sizable oscillator strengths do not play any role in determining neither the C nor the O K-edge spectral pattern of 0. The higher π-acceptor capability of the CO ligand, regardless of its terminal or bridging coordination, with respect to [(η5-C5H5)]- is herein ultimately confirmed.

In this contribution we report on light-induced metal-free coupling of propynylbenzene molecular units on highly oriented pyrolytic graphite. The reaction occurs within the self-assembled monolayer and leads to the generation of covalently coupled 1,5-hexadiyne and para-terphenyl derivatives under topological control. Such photochemical uncatalysed pathway represents an original approach in the field of topological C-C coupling at the solid/liquid interface and provides new insight into the low temperature formation of aromatic compounds at the surface of carbonaceous supports.

International audience; Gold is an inert noble metal displaying superior chemical stability that renders it a suitable component for the manufacturing of electrodes for various types of devices. Despite being widely employed, the variation of gold surface properties occurring upon the material's exposure to ambient conditions have been often disregarded. While it is well-known that the contamination of a metallic surface can have a dramatic impact on its properties, the process of contamination itself is poorly understood. Changes of the work function by fractions of an electron-volt are commonly observed in gold surfaces that are processed at ambient laboratory conditions, but an exhaustive comprehension and control of this phenomenon are still lacking. Here, a multiscale characterization of Au(111) surfaces aiming to unravel the surface dynamics underlying the air contamination is presented. The visualization of the adventitious carbon contamination on Au(111) surface by atomic force microscopy is key to rationalize the mechanisms of surface reorganization ruling the change of Au work function between 5.25 and 4.75 eV by solely changing the storage conditions. Such a huge variation must be taken into account when optimizing the Au surface for both controlling its fundamental surface and interfacial physical processes, as well as its functional applications.

The ETS-NOCV bond analysis has been exploited to quantitatively estimate donation and back-donation properties of [(η5-C5H5)]−, CO, and FeI in the cis-/trans-[(η5-C5H5)Fe(η1-CO)(μ-CO)]2 (cis-I/trans-I) tautomers. Theoretical outcomes indicate that the Fe-CO bond, regardless to the CO monoapto (η1-) or bridging (μ-) coordination, has a sizeable π Fe → CO back-bonding contribution, which is stronger in trans-I than in cis-I. Moreover, [(η5-C5H5)]− has the weakest back-donation acceptor capability. The back-bonding behaviour of the Fe → η1-CO interaction well agrees with the experimental symmetric/antisymmetric infrared νCO (sνηjavax.xml.bind.JAXBElement@fc12185-CO/aνηjavax.xml.bind.JAXBElement@4c260f05-CO) trend for cis-I and trans-I and further confirms the infrared classical behaviour of the η1-CO group in this class of complexes.

In this paper we report on the use of an Ullmann-like aryl halide homocoupling reaction to obtain long Graphyne Molecular Wires (GY MWs) organized in dense, ordered arrays. Instead of using highly reactive terminal alkynes, we resort to a precursor wherein the acetylenic functional group is internal, namely protected by two phenyl rings, each bearing a Br atom in the para position to allow for linear homocoupling. In addition, two further factors concur with the production of dense and highly ordered arrays of very long GY MWs, namely the geometric compatibility between the substrate and both the organometallic intermediates and the final polymeric products of the synthesis, coupled with the presence of surface-adsorbed bromine atoms separating the MWs, which minimize inter-wire cross-linking secondary reactions.

Iron phthalocyanines (FePc) adsorbed onto a Ag(110) substrate self-assemble into different monolayer phases going from rectangular to different oblique phases, with increasing molecular density. We have investigated the oxygen uptake capability of the different phases and their associated magneto-structural changes. Our study combines scanning tunneling microscopy and spectroscopy (STM/STS), X-ray magnetic circular dichroism (XMCD), and density functional theory (DFT) calculations. STM measurements reveal that the oxygenation reaction of the FePc/Ag(110) generally involves a displacement and a rotation of the molecules, which affects the electronic state of the Fe centers. The oxygen intercalation between FePc and the substrate is greatly obstructed by the steric hindrance in the high-density phases, to the point that a fraction of oblique phase molecules cannot change their position after oxidizing. Depending on the oxidation state and adsoption geometry, the STS spectra show clear differences in the Fe local density of states, which are mirrored in the XAS and XMCD experiments. Particularly, XMCD spectra of the oxidized phases reflect the distribution of FePc species (nonoxygenated, oxygenated-rotated, and oxygenated-unrotated) in the different cases. Sum rule analysis yields the effective spin (mseff) and orbital (mL) magnetic moments of Fe in the different FePc species. Upon oxygenation, the magnetic moment of FePc molecules increases about an order of magnitude, reaching mTOT ∼ 2.2 μB per Fe atom., We acknowledge financial support from the Spanish MCINN Project (DWARFS MAT2017-83468-R) and the Aragonese Projects E12-17R RASMIA and E09-17R Q-MAD (co-funded by Fondo Social Europeo), and of the European Union FEDER (ES); from the University of Padova Grant CPDA154322 AMNES, and from the European Regional Development Fund (ERDF) under the program Interreg V-A España-Francia-Andorra (Contract EFA 194/16 TNSI). M.P. and A.M. are funded by the CERCA Program/Generalitat de Catalunya and the Severo Ochoa program from Spanish MINECO (Grant SEV-2017-0706).

The unoccupied electronic structures of three closed-shell, highly popular organoiron complexes ([Fe(CO)

The adsorption of tetrahydroxyquinone (THQ) on the Cu(111) surface at different temperatures gives rise to different ordered structures, unveiled by density functional theory (DFT) modelling of scanning tunnelling microscopy (STM) topography and by X-ray absorption spectroscopy (XAS) measurements. After annealing, the THQ films generated tetrameric Cu clusters embedded in a metal–organic tetraoxyquinone (TOQ) network, whose electronic properties were thoroughly studied. The remarkable agreement between the STM results and periodic calculations was exploited to model C and O K-edge XA spectra recorded before (room temperature, RT) and after annealing (high temperature, HT). The subsequent analysis of the C and O TOQ@Cu(111) K-edge XA spectra provides definitive information about the structural arrangement of the TOQ@Cu(111) coordination network, confirming the complete THQ dehydrogenation upon annealing, suggested by the simulations of the STM images. The obtained information is crucial to rationalize the evolution of THQ@Cu(111) upon heating, shedding light into the potential reactivity of the HT coordination network, and, more generally, to investigate the nature and character of low-lying virtual states, the most involved states in the chemical reactions.

This is an open access article published under an ACS AuthorChoice License.-- et al., The tunable properties of molecular materials place them among the favorites for a variety of future generation devices. In addition, to maintain the current trend of miniaturization of those devices, a departure from the present top-down production methods may soon be required and self-assembly appears among the most promising alternatives. On-surface synthesis unites the promises of molecular materials and of self-assembly, with the sturdiness of covalently bonded structures: An ideal scenario for future applications. Following this idea, we report the synthesis of functional extended nanowires by self-assembly. In particular, the products correspond to one-dimensional organic semiconductors. The uniaxial alignment provided by our substrate templates allows us to access with exquisite detail their electronic properties, including the full valence band dispersion, by combining local probes with spatial averaging techniques. We show how, by selectively doping the molecular precursors, the product's energy level alignment can be tuned without compromising the charge carrier's mobility., This work was partially funded by MIUR (PRIN 2010/11, Project 2010BNZ3F2: “DESCARTES”), by EU project PAMS (Agreement No. 610446), by the European Research Council (ERC) under the EU Horizon 2020 research and innovation programme (Grant Agreement No. 635919), by the European Community’s Seventh Framework Programme (FP7/2007-2013) CALIPSO under Grant Agreement No. 312284, by the Spanish Ministry of Science and Competitiveness (MINECO, MAT2013-46593-C6-6-P and MAT2013-46593-C6-4-P) and FEDER, by the Basque Government (Grant Nos. IT-621-13 and IT-627-13)) and by the University of Padova (Grant CPDA154322, Project AMNES).

Copper complexes of tetraphenylporphyrin (H2TPP) and tetrakis(pentafluorophenyl) porphyrin (H2TPP(F)) deposited as thin films on Au(111) have been studied experimentally and theoretically. Core level emissions from C 1s, N 1s, F 1s and Cu 2p as well as valence states of CuTPP and CuTPP(F) have been investigated using surface photoelectron spectroscopy. The interpretation of experimental results has been guided by theoretical calculations carried out on isolated species in the habit of the density functional theory. Reference to experimental and theoretical outcomes pertaining to H2TPP and H2TPP(F) allowed a confident and detailed assignment of the title molecules' X-ray and ultraviolet photoemission data. With specific reference to the latter, similar to copper phthalocyanine (CuPc), whose coordinative pocket mirrors the CuTPP/CuTPP(F) ones, the lowest ionization energy of the title compounds implies electron ejection from a ring orbital rather than from the Cu 3d-based singly occupied molecular orbital. Moreover, analogous to CuPc, the ionic contribution appears to play an important role in the Cu-N bonding. Nevertheless, differences in the number, symmetry, nature and relative position of CuTPP/CuTPP(F) occupied frontier orbitals compared to CuPc may be stated only by considering in great detail the Cu-ligand covalent interactions.

The structural, electronic, and spectroscopic properties of high- and intermediate-spin transition metal phthalocyaninato complexes (MPc, M = V, Cr, Mn and Fe) have been theoretically investigated to look into the origin, symmetry and strength of the M&ndash, Pc bonding. DFT calculations coupled to the Ziegler&rsquo, s extended transition state method and to an advanced charge density and bond order analysis allowed us to assess that the M&ndash, Pc bonding is dominated by s interactions, with FePc having the strongest and most covalent M&ndash, Pc bond. According to experimental evidence, the lightest MPcs (VPc and CrPc) have a high-spin ground state (GS), while the MnPc and FePc GS spin is intermediate. Insights into the MPc unoccupied electronic structure have been gained by modelling M L2,3-edges X-ray absorption spectroscopy data from the literature through the exploitation of the current Density Functional Theory variant of the Restricted Open-Shell Configuration Interaction Singles (DFT/ROCIS) method. Besides the overall agreement between theory and experiment, the DFT/ROCIS results indicate that spectral features lying at the lowest excitation energies (EEs) are systematically generated by electronic states having the same GS spin multiplicity and involving M-based single electronic excitations, just as systematically, the L3-edge higher EE region of all the MPcs herein considered includes electronic states generated by metal-to-ligand-charge-transfer transitions involving the lowest-lying p* orbital (7eg) of the phthalocyaninato ligand.

The challenge of synthesizing graphene nanoribbons (GNRs) with atomic precision is currently being pursued along a one-way road, based on the synthesis of adequate molecular precursors that react in predefined ways through self-assembly processes. The synthetic options for GNR generation would multiply by adding a new direction to this readily successful approach, especially if both of them can be combined. We show here how GNR synthesis can be guided by an adequately nanotemplated substrate instead of by the traditionally designed reactants. The structural atomic precision, unachievable to date through top-down methods, is preserved by the self-assembly process. This new strategy’s proof-of-concept compares experiments using 4,4′′-dibromo-para-terphenyl as a molecular precursor on flat Au(111) and stepped Au(322) substrates. As opposed to the former, the periodic steps of the latter drive the selective synthesis of 6 atom-wide armchair GNRs, whose electronic properties have been further characterized in detail by scanning tunneling spectroscopy, angle resolved photoemission, and density functional theory calculations., The project leading to this publication has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant Agreement No 635919), from the Spanish Ministry of Economy, Industry and Competitiveness (MINECO, Grant No. MAT2016-78293-C6), from the Basque Government (Grant No. IT-621-13), from the regional Government of Aragon (RASMIA Project), and from the University of Padova (Grant CPDA154322, Project AMNES).

Dioxygen adsorbs in the end-on configuration on-top of the Fe atoms of an iron phthalocyanine monolayer supported on Ag(100) and is partly cleaved at room temperature to produce O/FePc/Ag(100). Scanning tunnelling microscopy coupled to density functional theory calculations gives the first experimental evidence of the substrate involvement in the O2 bond dissociation.

The electronic properties of three vanadium phthalocyaninato (Pc) based complexes (PcV, PcVO, and PcVI; I-III, respectively) were theoretically investigated and corresponding VL2,3-edge XAS spectra modeled. Ground state (GS) DFT outcomes indicated that II is more stable than III by 141 kcal/mol; moreover, the Ziegler transition state method allowed us to estimate the PcV-X bond dissociation energy and to quantify ?/? contributions to the V-X interaction. As such, the Nalewajski-Mrozek V-X and V-N bond multiplicity indexes (V-O/V-I = 2.48/1.22; V-N = 0.64, 0.51, and 0.58 in I-III, respectively) state that the V-X bond strength and nature affect the V-N interaction. The coordination of X to V in the I -> II/I -> III reactions implies the transfer of two/one electrons from I to X. In both cases, the oxidation involves only the V ion; moreover, V 3d based orbitals from which electrons are transferred were identified. Literature I/IIL2,3-edge XAS data were modeled by exploiting the DFT/ROCIS method. The same protocol was adopted to predict IIIL2,3-edge XAS spectra. Theoretical results indicated that, along the whole series, spectral features lying at the lowest excitation energies (EEs) are mostly generated by states having the same GS spin multiplicity and involve 2pV -> SOMO (single occupied molecular orbital) single electronic excitations. XAS features at higher EEs include only states with the same GS spin multiplicity in I, while states with both ?S = 0 and ?S = +1 (S = total spin quantum number) are present in II and III with significant, in some cases prevailing, contributions from metal to ligand charge transfer (MLCT) excitations. Beyond the role played by MLCT transitions in determining XAS patterns, it is noteworthy that they involve only Pc-based empty orbitals with no participation of the X-based virtual levels.

The consequences of the evolution of the active site in the oxygen reduction reaction catalyzed by iron phthalocyanine (FePc) submonolayers deposited on the Ag(110) surface are explored. The capacity of reversibly and sharply switching the magnetic state of FePc molecules by chemical means is conclusively evidenced by X-ray magnetic circular dichroism (XMCD) at the Fe L2,3 absorption edge. In the molecular oxygen-dosed phase, oxygen intercalates between the molecule and the surface, thereby switching the Fe magnetic moment from a nearly negligible (mTotexp ≈ 0.26(1) μB) to an order of magnitude larger value (mTotexp ≈ 2.1(2) μB). Moreover, the characteristic XMCD spectrum undergoes a crossover from metallic to oxidized Fe(III)-like line shape, in accordance with an oxygen-induced decoupling of the molecular electronic states from the underlying metal surface. The FePc acts as a reversible bifunctional chemical–magnetic switch at the atomic monolayer scale., Financial support from the projects MINECO MAT2011/23791, MAT2014-53921-R, and DGA IMANA E34, as well as MIUR project PRIN 2010BNZ3F2 “DESCARTES” and Progetti di Ricerca di Ateneo, (CPDA118475/11) are acknowledged here.

High surface-to-volume ratio Co3O4/TiO2 heterojunctions were fabricated by combining different methods. Atomic layer deposition (ALD) and a photochemical method were used to coat polystyrene (PS) 3D-Direct Opal (3D-DO) structures on conductive ITO substrates. Firstly, 3D-DO of PS were crystallized on ITO substrates to form the high surface-to-volume ratio template via a self-assembly method. A low-temperature ALD TiO2 film was infiltrated onto the PS opal structure. Then, the PS template was removed by a thermal treatment in air at 450 °C for 5 h. Hollow anatase phase nanospheres were obtained, crystallized in a face centered cubic (FCC) lattice with the (111) plane oriented parallel to the substrate surface. Finally, the hollow TiO2 nanospheres were coated with Co3O4 via a photochemical method. This ordered 3D nanostructure with designed morphology may find applications as surface-enhanced materials for photovoltaic devices. TiO2 hollow nanospheres obtained via low-pressure ALD (a) and Co3O4/TiO2 heterostructure (scanned region: 1.5 μm) (b).

We report on a stepwise on-surface polymerization reaction leading to oriented graphene nanoribbons on Au(111) as the final product. Starting from the precursor 4,4″-dibromo-p-terphenyl and using the Ullmann coupling reaction followed by dehydrogenation and C-C coupling, we have developed a fine-tuned, annealing-triggered on-surface polymerization that allows us to obtain an oriented nanomesh of graphene nanoribbons via two well-defined intermediate products, namely, p-phenylene oligomers with reduced length dispersion and ordered submicrometric molecular wires of poly(p-phenylene). A fine balance involving gold catalytic activity in the Ullmann coupling, appropriate on-surface molecular mobility, and favorable topochemical conditions provided by the used precursor leads to a high degree of long-range order that characterizes each step of the synthesis and is rarely observed for surface organic frameworks obtained via Ullmann coupling.

The unoccupied electronic structure of tetrakis(phenyl)- and tetrakis(pentafluorophenyl)-porphyrin thick films deposited on SiO2/Si(100) native oxide surfaces has been thoroughly studied by combining the outcomes of near-edge X-ray absorption fine structure spectroscopy at the C, N, and F K-edges with those of scalar relativistic zeroth order regular approximation time-dependent density functional theory calculations carried out on isolated molecules. Both experimental and theoretical results concur to stress the electronic inertness of pristine porphyrin macrocycle based 1sC -> ?* and 1sN -> ?* transitions whose excitation energies are substantially unaffected upon fluorination. The obtained results complement those published by the same group about the occupied states of both molecules, thus providing the missing tile to get a thorough description of the halide decoration effects on the electronic structure of the tetrakis(phenyl)-porphyrin.

The surface-assisted synthesis of gold-organometallic hybrids on the Au(111) surface both by thermo- and light-initiated dehalogenation of bromo-substituted tetracene is reported. Combined X-ray photoemission (XPS) and scanning tunneling microscopy (STM) data reveal a significant increase of the surface order when mild reaction conditions are combined with 405 nm light irradiation.

Single- and multi-boron, nitrogen, sulphur doped graphene oxide quantum dots and three-dimensional foams are synthesized by a simple and environmentally friendly electrochemical method. The electrochemical activity of these materials in the oxygen reduction reaction is investigated by cyclic voltammetry and rotating disk electrode measurements. The experimental data demonstrate that the reaction selectivity is controlled by the oxidation degree of the materials: as-prepared graphene oxide quantum dots, which present highly oxidized functional groups, follow a two-electron reduction pathway and produce hydrogen peroxide, whereas after a reduction treatment by NaBH4, the same materials favour a four-electron reduction of oxygen to water. The high selectivity and high efficiency of the graphene oxide quantum dots for the production of hydrogen peroxide can be efficiently used for water remediation applications (phenol decomposition).

We report on the assembly of a highly ordered array of copper tetrameric clusters, coordinated into a metal-organic network. The ordered cluster array has been achieved by the deposition of tetrahydrox- yquinone molecules on the Cu(111) surface at room temperature, and subsequent thermally activated dehydrogenation with the formation of tetraoxyquinone tetra-anions with a 4 × 4 periodicity. The16 supramolecular organic network acts as a spacer for the highly ordered two-dimensional network of copper tetramers at the very surface.

The occupied and unoccupied electronic structures of three high spin TM(acac) 3 (TM = Cr, Mn, and Fe) complexes (I, II, and III, respectively) were studied by revisiting their literature vapour- phase He(I) and, when available, He(II) photoemission (PE) spectra and by means of original near- edge X- ray absorption fine structure (NEXAFS) spectroscopic data recorded at the OK-edge (OK-edge) and TM (L2,3)- edges (TML2,3- edges). The assignments of the vapour-phase He(I)/He(II) PE spectra were guided by the results of spin- unrestricted non- relativistic Slater transition state calculations, while the OK- edge and TM(L2,3)edge spectroscopic pieces of evidence were analysed by exploiting the results of spin-unrestricted scalar-relativistic time-dependent density functional theory (DFT) and DFT/ROCIS calculations, respectively. Although the actual symmetry (D-3, in the absence of any Jahn-Teller distortion) of the title molecules allowed an extensive mixing between TM t(2g)- like and eg- like atomic orbitals, the use of the Nalewajski- Mrozek TM-O bond multiplicity index combined with a thorough analysis of the ground state (GS) outcomes allowed the assessment of the TM-O bond weakening associated with the progressive TM 3d- based e(g)- like orbital filling. The experimental information provided by K-O- edge spectra was rather poor; nevertheless, the combined use of symmetry, orbitals and spectra allowed us (i) to rationalise minor differences characterizing spectral features along the series, (ii) to quantify the contribution provided by the ligand-to-metal-charge-transfer (LMCT) excitations to the different spectral features, and (iii) to recognize the t2g-/eg- like nature of the TM 3d- based orbitals involved in LMCT transitions. As far as the TML2,3- edge spectra and the DFT/ROCIS results were concerned, the lowest lying L-I, II(3) spectral features included states having either the GS spin multiplicity (S(I) = 3/2, S(II) = 2) or, at higher excitation energies (EEs), states with Delta S = +/- 1. In contrast to that, only states with Delta S = 0, -1 significantly contributed to the IIIL3 spectral pattern. Along the whole series, the L-3 higher EE side was systematically characterized by states involving (TM)2p pi(4) MLCT excitations; as such, coupled- single excitations with DS = 0 were involved in I and II, while single MLCT (TM)2p pi(4) transitions with Delta S = -1 were involved in III.

The DFT/ROCIS method has been used to model the Mn(acac)2 (I) and Mn(acac)3 (II) L2,3-edges absorption spectra. Non-hybrid (BP86 and PBE), hybrid (B3P, PBE0 and B3LYP) and hybrid meta-GGA (M06) functionals have been considered to test their efficiency in reproducing experimental features. Structural parameters of both I and II are scarcely affected by the functional selection and the same holds as far as the IL2,3-edges absorption spectrum is concerned. At variance to that, the use of the hybrid meta-GGA functional is decisive for a detailed assignment of the IIL2,3-edges spectral features. The role played by the structural arrangement about the central Mn ion appears less important than the Mn oxidation number in determining the overall spectrum appearance and the spectral features’ excitation energies (EEs). DFT/ROCIS results indicate that, both in I and II, the lower EE side of the L3 intensity distribution mainly includes states having the ground state spin multiplicity (S = 5/2 in I and S = 2 in II), whereas states with different spin multiplicity contribute, both in I and II, to the L3 higher EE side. The occurrence of states involving metal to ligand charge transfer transitions and implying low lying empty ligand-based orbitals on the I/IIL3 higher EE sides has been further confirmed herein.

Due to the donor–acceptor nature of their supramolecular interactions, nanostructured porphyrin-fullerene self-assembled architectures show attractive properties that can be exploited in high efficiency solar cells. In this work, we show that six different ordered bicomponent porphyrin-fullerene (C60) networks are obtained by controlling the peripheral functionalization of meso-tetraphenylporphyrins (TPP) with amino groups and the stoichiometry of their aggregates with C60 on Ag (110). Such networks can be grouped in two general classes, depending on their structural habit: the so-called “stripes” phases, formed by alternating monomolecular stripes of C60 and TPP, and the so-called “pores” phases, where a fullerene net accommodates isolated TPP molecules in nanometer-sized pores. These phases are of general interest in the field of surface-supported electron donor–acceptor systems, since they represents a rare example of fullerene-containing surface-supported bicomponent supramolecular networks where the ...

L2,3 spectra of Cu(ii) complexes have been simulated by means of time dependent DFT. Besides the agreement between theory and experiment, the adopted approach provided further insights into the use of the Cu(ii) L3-edge intensity and position to investigate the Cu–ligand symmetry-restricted covalency and the ligand-field strength.

On-surface synthesis involving the homocoupling of aryl-alkynes affords the buildup of bisacetylene derivatives directly at surfaces, which in turn may be further used as ingredients for the production of novel functional materials. Generally, homocoupling of terminal alkynes takes place by thermal activation of molecular precursors on metal surfaces. However, the interaction of alkynes with surface metal atoms often induces unwanted reaction pathways when thermal energy is provided to the system. In this contribution we report about light-induced metal-free homocoupling of terminal alkynes on highly oriented pyrolitic graphite (HOPG). The reaction occurred with high efficiency and selectivity within a self-assembled monolayer (SAM) of aryl-alkynes and led to the generation of large domains of ordered butadiynyl derivatives. Such a photochemical uncatalyzed pathway represents an original approach in the field of topological C–C coupling at the solid/liquid interface.

L-edges absorption spectra of FePc (I) and FePc(η-O) (II) on Ag(110) have been modelled using the DFT/ROCIS method. Despite disregarding the presence of the substrate, the agreement between experiment and theory is remarkable. Moreover, theoretical results confirm the fraction of II (70%) present on the surface, thus allowing a thorough assignment of each experimental spectral feature. Ground state (GS) theoretical outcomes pertaining to I and II provide an intimate understanding of the electron transfer pathway ruling the I-based catalytic oxygen reduction reaction. DFT/ROCIS outcomes indicate that the lower excitation energy (EE) side of the L intensity distributions mainly includes states having the GS number of unpaired electrons (two in I and six in II), whereas states with higher/lower spin multiplicity contribute to the L higher EE side. The occurrence of states involving metal to ligand charge transfer transitions implying low lying empty π∗ ligand-based orbitals on the L higher EE sides have been confirmed., The Italian Ministry of the University and Research (PRIN-2010BNZ3F2, project DESCARTES), the University of Padova (CPDA134272/13, project S3MArTA), and the Computational Chemistry Community (C3P) of the University of Padova are kindly acknowledged. This work has been partially financed by the Spanish projects MINECO MAT2014-53921-R and DGA IMANA E34.

The unoccupied electronic structure of thick films of tetraphenylporphyrin and tetrakis(pentafluorophenyl)porphyrin Cu(II) complexes (hereafter, CuTPP and CuTPP(F)) deposited on Au(111) has been studied by combining the outcomes of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy with those of spin-unrestricted time-dependent density functional (TD-DFT) calculations carried out either within the scalar relativistic zeroth order regular approximation (ZORA) framework (C, N and F K-edges) or by using the Tamm-Dancoff approximation coupled to ZORA and including spin-orbit effects (Cu L-2,L-3-edges). Similarly to the modelling of NEXAFS outcomes pertaining to other Cu(II) complexes, the agreement between theory and experiment is more than satisfactory, thus confirming the open-shell TD-DFT to be a useful tool to look into NEXAFS results pertinent to Cu(II) compounds. The combined effect of metalation and phenyl (Ph) fluorine decoration is found to favour an extensive mixing between (Ph)sigma* and pristine porphyrin macrocyle (pmc) (pmc)pi* virtual levels. The lowest lying excitation in the C and N K-edge spectra of both CuTPP and CuTPP(F) is associated with a ligand-to-metal-charge-transfer transition, unambiguously revealed in the N-CuTPP K-edge spectral pattern. Moreover, the comparison with literature data pertaining to the modelling of the L-Cu(II)(2,3) features in the phthalocyanine-Cu(II) (CuPc) complex provided further insights into how metal-to-ligand-charge-transfer transitions associated with excitations from 2p(Cu(II)) AOs to low-lying, ligand-based pi* MOs may contribute to the Cu(II) L-2,L-3-edge intensity and thus weaken its believed relationship with the Cu(II)-ligand symmetry-restricted covalency. Despite the coordinative pocket of CuTPP/CuTPP(F) mirroring CuPc, the ligand-field strength exerted by the phthalocyanine ligand on the Cu(II) centre is experimentally found and theoretically confirmed to be slightly stronger than that experienced by Cu in CuTPP and CuTPP(F). On the whole, the obtained results complement those published in the near past by the same group on the occupied and empty states of the H2TPP and H2TPP(F) free ligands as well as on the occupied states of both CuTPP and CuTPP(F), thus providing the final piece to get a thorough description of electronic perturbations associated with the metalation and the Ph halogen decoration of H2TPP.

Mn(acac)2 (I) and Co(acac)2 (II) L2,3-edge absorption spectra have been modeled using the DFT/ROCIS method. In addition to the agreement between experiment and theory, the combined use of the B3LYP exchange-correlation functional and the def2-TZVP(-f) basis set provided useful information about the coordinative geometry around the M(ii) ions as well as about the nature and the strength of the Mn-O and Co-O interaction. The lower excitation energy (EE) side of both (I)(/)(II)L3 and (I)(/)(II)L2 intensity distributions mainly includes states having ground state spin multiplicity (S = 5/2 in I and S = 3/2 in II), whereas states with lower spin multiplicity (S = 3/2 in I and S = 1/2 in II) significantly contribute to the higher EE side of both (I)(/)(II)L3 and (I)(/)(II)L2. Hence, the occurrence of states involving metal to ligand charge transfer transitions in the presence of ligands with low lying empty π* orbitals on the L3 and L2 higher EE sides is herein confirmed.

A novel two-step bottom-up approach to construct a 2D long-range ordered, covalently bonded fullerene/porphyrin binary nanostructure is presented: in the first place, reversible supramolecular interactions between C60 and 5,15-bis(4-aminophenyl)-10,20-diphenylporphyrin are exploited to obtain large domains of an ordered binary network, subsequently a reaction between fullerene molecules and the amino-groups residing on porphyrin units, triggered by thermal treatment, is used to freeze the supramolecular nanostructure with covalent bonds. The resulting nanostructure resists high temperature treatments as expected for an extended covalent network, whereas very similar fullerene/porphyrin nanostructures held together only by weak interactions are disrupted upon annealing at the same or at lower temperatures.

A semiempirical addition of dispersive forces to conventional density functionals (DFT-D) has been implemented into a pseudopotential plane-wave code. Test calculations on the benzene dimer reproduced the results obtained by using localized basis set, provided that the latter are corrected for the basis set superposition error. By applying the DFT-D/plane-wave approach a substantial agreement with experiments is found for the structure and energetics of polyethylene and graphite, two typical solids that are badly described by standard local and semilocal density functionals. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009

Au nanoparticles deposited on titania films, where two nanophases of different stoichiometry and defectivity are co-present, were imaged on the same spot by scanning tunneling microscopy. The observed sizes are rather dissimilar as a consequence of the different mobility of An on the two surfaces. The role of the stoichiometry, which can influence the Au-substrate interaction, and of the defects, which can trap the metal atoms, is discussed on the basis of theoretical calculations of diffusion energy barriers on the two surfaces.

Thermal self-assembly of C-60 on (1 x 2)-Pt(110) following room-temperature deposition has been studied by means of scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and density functional theory (DFT) calculations. Two distinct C-60 chemisorption phases have been identified and characterized as a function of the annealing temperature. After a thermal treatment at 700 K, islands of a C-60 quasi-hexagonal lattice form. These islands are characterized by the highest surface density so far reported for a two-dimensional surface-supported fullerene phase (the surface area per molecule is 87.0 angstrom(2)), with intermolecular nearest-neighbor distances equal to 9.6 +/- 0.1 angstrom. Embedded nanowires of fullerene dumbbell dimers (with an intermolecular distance equal to 9.2 +/- 0.1 A) occasionally nucleate within this high-density phase following a "molecular zip" mechanism. Highly site selective chemisorption driven by the particularly strong overlayer-substrate bonding is proposed to be responsible for the first reported example of surface-templated chemical bond formation between fullerene molecules. After annealing at 850 K, an oblique C-60 chemisorption phase forms. This is characterized by a tetramolecular basis associated to each lattice point of the two-dimensional superstructure and by a peculiar bright-dim contrast in STM images acquired at positive sample bias values. The combination of high-resolution STM images with LEED data and DFT calculations leads to the conclusion that the (1 x 2) substrate reconstruction is lifted at the fullerene-platinum interface and also provides a detailed description of the molecular bonding sites and orientations found within the phase. It is proposed that the main factor ruling the interconversion of chemisorption phases is the variation of substrate atom mobility as a function of temperature.

Photochemically activated reactions, despite being a powerful tool to covalently stabilize self-organized molecular structures on metallic surfaces, have struggled to take off due to several not yet well understood light-driven processes that can affect the final result. A thorough understanding of the photoinduced charge transfer mechanisms at the organic/metal interface would pave the way to controlling these processes and to developing on-surface photochemistry. Here, by time-resolved two-photon photoemission measurements, we track the relaxation processes of the first two excited molecular states at the interface between porphyrin, the essential chromophore in chlorophyll, and two different orientations of the silver surface. Due to the energy alignment of the porphyrin first excited state with the unoccupied sp-bands, an indirect charge transfer path, from the substrate to the molecule, opens in porphyrin/Ag(100) 250 fs after the laser pump excitation. The same time-resolved measurements carried out on porphyrin/Ag(111) show that in the latter case such an indirect path is not viable.

The low-lying empty orbitals of bis(acetylacetonato)copper have been probed by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy at the Cu L2,3 edges and time-dependent density functional theory (TDDFT) calculations within the Tamm-Dancoff approximation (TDA) coupled to the relativistic zeroth-order regular approximation including spin-orbit effects (SO-ZORA TDDFT-TDA). Both the relative positions of NEXAFS features and their linear dichroism are satisfactorily reproduced. Moreover, a comparison with literature data pertaining to two other square-planar CuII complexes ([CuCl4]2- and copper phthalocyanine) provided information about how metal-to-ligand charge-transfer transitions associated with excitations from CuII 2p orbitals to low-lying, ligand-based ?* molecular orbitals in a simplified one-electron picture may contribute to the CuII L2,3 edge intensity and, thus, weaken its believed relationship with the CuII-ligand symmetry-restricted covalency.

The growth of ultrathin nickel oxide overlayers (nanolayers) on Pd(1 0 0) from submonolayer coverages up to 20 monolayer thick films has been investigated by scanning tunneling microscopy (STM), in conjunction with LEED and high-resolution electron energy loss spectroscopy (HREELS). The first nickel oxide monolayer on Pd(1 0 0) forms a wetting layer with a c(4 × 2) structure, which has been interpreted in terms of an interface stabilised Ni3O4-type structure. Stoichiometric NiO grows on top of the c(4 × 2) monolayer in a strained lattice with the (1 0 0) surface orientation parallel to the substrate. The lattice relaxation of the NiO phase occurs gradually and is completed after ∼10 monolayers, where a bulk-type NiO phase is obtained. The phonon spectra of the c(4 × 2) monolayer and the subsequent NiO layers, as measured by HREELS, are characteristic and of diagnostic value to identify the different oxide phases. The morphology of the nickel oxide nanolayers has been analysed by quantitative evaluation of the STM images in terms of their roughness parameters. The roughness of nickel oxide nanolayers prepared by different kinetic routes has been compared and the optimal preparation conditions for obtaining smooth morphologies are proposed.

Periodic density functional calculations have been used to investigate the structure and stability of epitaxial vanadium oxide films grown on the TiO(2)(001) anatase surface. The formation energy of films of V(2)O(5) stoichiometry, initially low, is found to rapidly increase with the film thickness, at variance to what is obtained for reduced pseudomorphic VO(2) films. This is in tune with results of oxygen-assisted molecular beam epitaxy. The oxidation of thick, viz.2 monolayers (ML), VO(2) films yields a c(2 x 2) reconstructed surface, in agreement with low energy electron diffraction. These films are composed by partially reduced inner V atoms in a distorted-octahedral environment, and by isolated surface dioxovanadium centers exhibiting a distorted trigonal-bipyramidal coordination. Single scattering simulations of X-ray photoelectron diffraction patterns have also been performed, taking both 2- and 3-ML surface surface-oxidized films as models. Results are in fair agreement with experiments referring to films grown in oxidizing conditions, which suggests that coherent vanadia ultrathin films could be formed in vanadia-titania catalysts. The electronic structure of the films has been finally studied, finding that the terminal oxygens carried by the surface dioxovanadium species have a strong nucleophilic character, which makes them potential active centers for selective oxidation catalysis.