Synthesis of mesoscale ordered two-dimensional π-conjugated polymers with semiconducting properties

Two-dimensional materials with high charge carrier mobility and tunable band gaps have attracted intense research effort for their potential use in nanoelectronics. Two-dimensional π-conjugated polymers constitute a promising subclass because the band structure can be manipulated by varying the molecular building blocks while preserving key features such as Dirac cones and high charge mobility. The major barriers to the application of two-dimensional π-conjugated polymers have been the small domain size and high defect density attained in the syntheses explored so far. Here, we demonstrate the fabrication of mesoscale ordered two-dimensional π-conjugated polymer kagome lattices with semiconducting properties, Dirac cone structures and flat bands on Au(111). This material has been obtained by combining a rigid azatriangulene precursor and a hot dosing approach, which favours molecular diffusion and eliminates voids in the network. These results open opportunities for the synthesis of two-dimensional π-conjugated polymer Dirac cone materials and their integration into devices.

Temperature-induced molecular reorganization on Au(111) driven by oligomeric defects

The formation of ordered molecular structures on surfaces is determined by the balance between molecule-molecule and molecule-substrate interactions. Whether the aggregation process is guided by non-covalent forces or on-surface reactions, a deeper understanding of these interactions is pivotal to formulating a priori predictions of the final structural features and the development of bottom-up fabrication protocols. Theoretical models of molecular systems corroborate the information gathered through experimental observations and help explain the thermodynamic factors that underpin on-surface phase transitions. Here, we report a scanning tunneling microscopy investigation of a tribromo-substituted heterotriangulene on the Au(111) surface, which initially forms an extended close-packed ordered structure stabilized by BrBr halogen bonds when deposited at room temperature. X-ray photoelectron spectroscopy reveals that annealing the self-assembled layer induces a fraction of the molecular precursors to partially dehalogenate that in turn leads to the formation of a less stable BrO non-covalent network which coexists with the short oligomers. Density functional theory (DFT) and Monte Carlo (MC) simulations illustrate how dimer moieties act as defects whose steric hindrance prevents the retention of the more stable configuration. A small number of dimers is sufficient to drive the molecular reorganization into a lower cohesive energy phase. Our study shows the importance of a combined DFT - MC approach to understand the evolution of molecular systems on substrates.

Binding geometry of hydrogen-bonded chain motif in self-assembled gratings and layers on Ag(111)

Upon adsorption on the (111) facet of Ag, 4-[trans-2-(pyrid-4-yl-vinyl)] benzoic acid (PVBA) self-assembles into a highly ordered, chiral twin chain structure at submonolayer coverages with domains that can extend for micrometers in one dimension. Using polarization-dependent measurements of C and N K-shell excitations in near-edge X-ray absorption fine structure (NEXAFS) spectra, we determine the binding geometry of single PVBA molecules within this unique ensemble for both low and high coverage regimes. At submonolayer coverage, the molecule is twisted to facilitate the formation of hydrogen bonds. The gas-phase planarity is gradually recovered as the coverage is increased, with complete planarity coinciding with loss of order in the overlayer. Thermal treatment of the PVBA film results in deprotonation of the carboxyl tail of the molecule, but despite the suppression of the stabilizing hydrogen-bonds, the overlayer remains ordered.

Resonant circular dichroism of chiral metal-organic complex

A sizable enhancement of the circular dichroism in photoelectron spectroscopy has been measured and computed for the metal complex Δ-cobalt(III) tris-acetylacetonate highest occupied molecular orbital state in the region of the Co 3p→3d Fano resonance. In the resonance the dichroism reaches the maximum value of 5% and even changes its sign as compared to the direct photoionization channel. We ascribe this enhancement to electron correlation processes, namely, with the coupling between discrete excitations and the continuum, which is correctly described in the time dependent density functional theory (TDDFT) framework. These findings open new physical aspects of photoelectron circular dichroism that now can be interpreted not only via the simple direct ionization, but also through more complex electron correlation processes.

Chirality transfer from a single chiral molecule to 2D superstructures in alaninol on the Cu(100) surface

The formation of 2D chiral monolayers obtained by self-assembly of chiral molecules on surfaces has been widely reported in the literature. Control of chirality transfer from a single molecule to surface superstructures is a challenging and important aspect for tailoring the properties of 2D nanostructures. However, despite the wealth of investigations performed in recent years, how chiral transfer takes place on a large scale still remains an open question. In this paper we report a coupling of scanning tunneling microscopy and low energy electron diffraction measurements with an original theoretical approach, combining molecular dynamics and essential dynamics with density functional theory, to investigate self-assembled chiral structures formed when alaninol adsorbs on Cu(100). The peculiarity of this system is related to the formation of tetrameric molecular structures which constitute the building blocks of the self-assembled chiral monolayer. Such characteristics make alaninol/Cu(100) a good candidate to reveal chiral expression changes. We find that the deposition of alaninol enantiomers results in the formation of isolated tetramers that are aligned along the directions of the substrate at low coverage or when geometrical confinement prevents long-range order. Conversely, a rotation of 14° with respect to the Cu(100) unit vectors is observed when small clusters of tetramers are formed. An insight to the process leading to a 2D globally chiral surface has been obtained by monitoring molecular assemblies as they grow from the early stages of adsorption, suggesting that the distinctive orientation of the self-assembled monolayer originates from a balance of cooperating forces which start acting only when tetramers pack together to form small clusters.

The valence electronic structure and conformational flexibility of epichlorohydrin

The electronic structure of epichlorohydrin is investigated in the whole valence region by a combined experimental and theoretical study. The issue of controversial assignments of the molecular electronic structure is here addressed. Photoelectron spectra (PES) and Threshold Photoelectron spectra (TPES) of room temperature molecules in the gas phase are recorded. Geometries and energies of the stable conformers due to internal rotation of the C-C-C-Cl dihedral angle, gauche-II (g-II), gauche-I (g-I), and cis, are calculated, and the effect of the conformational flexibility on the photoionization energetics is studied by DFT and 2h-1p Configuration Interaction (CI) methods. Strong breakdown of the Koopmans Theorem (KT) is obtained for the four outermost ionizations, which are further investigated by higher level ab initio calculations. The full assignment of the spectrum is put on a firm basis by the combination of experimental and theoretical results. The orbital composition from correlated calculations is found closer to the DFT orbitals, which are then used to analyze the electronic structure of the molecule. The Highest Occupied Molecular Orbital (HOMO) and HOMO--2 are n(O)/n(Cl) mixed orbitals. The nature of each valence MO is generally preserved in all the conformers, although the magnitude of the n(O)/n(Cl) mixing in HOMO and HOMO--2 varies to some extent with the C-C-C-Cl dihedral angle. The low energy part of the HOMO PE band is predicted to be substantially affected by the conformational flexibility, as experimentally observed in the spectra. The rest of the spectrum is described in terms of the dominant conformer g-II, and a good agreement between experiment and theory is found. The inner-valence PE spectrum is characterized by satellite structures, due to electron correlation effects, which are interpreted by means of 2h-1p CI calculations.

Vibrational state dependence of β and D asymmetry parameters: The case of the highest occupied molecular orbital photoelectron spectrum of methyl-oxirane

The beta angular asymmetry and D dichroic asymmetry parameters of the methyl-oxirane highest occupied molecular orbital (HOMO) band have been experimentally investigated with vibrational resolution using synchrotron radiation. A theoretical calculation of the Franck-Condon factors between vibrational ground state and different ionic vibrational states, in the Born-Oppenheimer harmonic approximation, has been performed in order to gain information on the vibrational states mainly involved in the HOMO photoelectron band. The general good agreement between theoretical and experimental results allows a reliable assignment of the major features. The experimental determination of beta and D shows their dependence on the different final vibrational states. This paper reports, for the first time, experimental evidence of the dependence of the dichroic D parameter on the vibrational excitation of the ion.

Valence photoionization dynamics in circular dichroism of chiral free molecules: the methyl-oxirane

The dynamical behavior of circular dichroism for valence photoionization processes in pure enantiomers of randomly oriented methyl-oxirane molecules has been studied by circularly polarized synchrotron radiation. Experimental results of the dichroism coefficient obtained for valence photoionization processes as a function of photon energy have been compared with theoretical values predicted by state-of-the-art ab initio density-functional theory. The circular dichroism measured at low electron kinetic energies was as large as 11%. Trends in the experimental dynamical behavior of the dichroism coefficients D(i)(omega) have been observed. Agreement between experimental and theoretical results permits unambiguous identification of the enantiomer and of the individual orbitals.

[Mortality of psychiatric patients. A retrospective cohort study of in-patients at the Psychiatric Hospital of Reggio Emilia]

The authors report the results of historical cohort study in long-term patients of psychiatric hospitals in Reggio Emilia. The cohort was formed by 790 patients hospitalized before 1978, and has been followed-up until 31/12/'89. The results of the study are: 269 subjects deceased (34%); 117 discharges (14.8%) and 411 (52.1%) still in hospital on 1/1/'90. An excess mortality was observed in the cohort. Mortality appears to be particularly high among young patient and females.

[Acting out and schizoid personality]

The Authors examine the crime-symptoms, sole index of an asymptomatic clinic history, and make some remarks on the indexes of social dangerousness. By this point of view, the structural traits of pre and post-critic personality seem to be a first predictory index. In relation to this question the Authors make mention to schizoidia.

[Intracoronary thrombolytic treatment with urokinase in myocardial infarct: clinical angiographic findings and effects on left ventricular function]

The effect of selective intracoronary thrombolysis was studied in 27 patients with evolving myocardial infarction. In the acute phase, angiography demonstrated complete occlusion in 22 cases (81,5%) (group A), and incomplete stenosis with diminished distal blood flow in 5 cases (18,5%) (group B). Urokinase was infused into the infarct-related coronary artery at a rate of 8000 u/min u/min until reperfusion was obtained and subsequently at a rate of 2-4000 u/min for 20-40 min. In group A, coronary recanalization was achieved in 18 of 22 patients (81,8%) (group A1), while in 4 patients (group A2) the procedure was unsuccessful. Group B patients showed no angiographic modifications following fibrinolytic therapy. Left ventricular function was studied during the acute phase (before and after therapy) in 9 patients; 22 patients were studied immediately after thrombolysis and before hospital discharge. Preliminary studies of patients in group A1 after reperfusion showed a decrease in telediastolic pressure from 18,9 to 24,4 mmHg and an increase in ejection fraction from 0,40 to 0,43 (p = ns). No modifications in these parameters were observed in group A2 or B. Follow-up examination of group A, revealed an increase in ejection fraction from 0,40 +/- 0,12 to 0,50 +/- 0,15 (p less than 0,05) and a decrease in the length of the akinetic segment from 6,49 +/- 2,4 to 4,40 +/- 1,35 (p less than 0.05). In group B, the ejection fraction increased from 0,41 +/- 0,06 to 0,50 +/- 0,04 (p less than 0.05) and the length of the akinetic segment decreased from 7,52 +/- 2,0 to 3,38 +/- 1,14 (p less than 0.05). On the contrary, in group A2, ejection fraction diminished from 0,39 +/- 0,06 to 0,34 +/- 0,07 and the length of the akinetic segment remained unchanged. Our results suggest that: A) coronary artery thrombosis is frequent in evolving myocardial infarction B) selective intracoronary thrombolysis and subsequent reperfusion of the infarcted area is readily obtainable with urokinase infusion C) no significant acute modifications of left ventricular function were observed D) 2-3 weeks after initial treatment, patients in which recanalization of an occluded vessel was achieved (group A1) and patients that presented with subocclusive stenosis and reduced blood flow (group B), showed an improvement in left ventricular function and a reduction in the akinetic area.