The Fe(II) spin crossover complex [Fe{H B(pz) } (bipy)] (pz = pyrazol-1-yl, bipy = 2,2'-bipyridine) can be locked in a largely low-spin-state configuration over a temperature range that includes temperatures well above the thermal spin crossover temperature of 160 K. This locking of the spin state is achieved for nanometer thin films of this complex in two distinct ways: through substrate interactions with dielectric substrates such as SiO and Al O , or in powder samples by mixing with the strongly dipolar zwitterionic p-benzoquinonemonoimine C H (-⋯ NH ) (-⋯ O) . Remarkably, it is found in both cases that incident X-ray fluences then restore the [Fe{H B(pz) } (bipy)] moiety to an electronic state characteristic of the high spin state at temperatures of 200 K to above room temperature; that is, well above the spin crossover transition temperature for the pristine powder, and well above the temperatures characteristic of light- or X-ray-induced excited-spin-state trapping. Heating slightly above room temperature allows the initial locked state to be restored. These findings, supported by theory, show how the spin crossover transition can be manipulated reversibly around room temperature by appropriate design of the electrostatic and chemical environment.

The two-dimensional self-assembly of a terbium(III) double-decker phthalocyanine on highly oriented pyrolitic graphite (HOPG) was studied by atomic force microscopy (AFM), and it was shown that it forms highly regular rectangular two-dimensional nanocrystals on the surface, that are aligned with the graphite symmetry axes, in which the molecules are organized in a rectangular lattice as shown by scanning tunneling microscopy. Molecular dynamics simulations were run in order to model the behavior of a collection of the double-decker complexes on HOPG. The results were in excellent agreement with the experiment, showing that-after diffusion on the graphite surface-the molecules self-assemble into nanoscopic islands which align preferentially along the three main graphite axes. These low dimension assemblies of independent magnetic centers are only one molecule thick (as shown by AFM) and are therefore very interesting nanoscopic magnetic objects, in which all of the molecules are in interaction with the graphite substrate and might therefore be affected by it. The magnetic properties of these self-assembled bar-shaped islands on HOPG were studied by X-ray magnetic circular dichroism, confirming that the compounds maintain their properties as single-molecule magnets when they are in close interaction with the graphite surface.

Optical metasurfaces-patterned arrays of plasmonic nanoantennas that enable the precise manipulation of light-matter interactions-are emerging as critical components in many nanophotonic materials, including planar metamaterials, chemical and biological sensors, and photovoltaics. The development of these materials has been slowed by the difficulty of efficiently fabricating patterns with the required combinations of intricate nanoscale structure, high areal density, and/or heterogeneous composition. One convenient strategy that enables parallel fabrication of periodic nanopatterns uses self-assembled colloidal monolayers as shadow masks; this method has, however, not been extended beyond a small set of simple patterns and, thus, has remained incompatible with the broad design requirements of metasurfaces. This paper demonstrates a technique-shadow-sphere lithography (SSL)-that uses sequential deposition from multiple angles through plasma-etched microspheres to expand the variety and complexity of structures accessible by colloidal masks. SSL harnesses the entire, relatively unexplored, space of shadow-derived shapes and-with custom software to guide multiangled deposition-contains sufficient degrees of freedom to (i) design and fabricate a wide variety of metasurfaces that incorporate complex structures with small feature sizes and multiple materials and (ii) generate, in parallel, thousands of variations of structures for high-throughput screening of new patterns that may yield unexpected optical spectra. This generalized approach to engineering shadows of spheres provides a new strategy for efficient prototyping and discovery of periodic metasurfaces.

The hysteresis of magnetization of the anionic, neutral, and cationic forms of a bis(phthalocyaninato)terbium-based complex ([Pc(2)Tb](-/0/+)) have been determined using magnetic circular dichroism (MCD) spectroscopy in frozen dilute solutions at low temperatures (1.5 K) showing that the three oxidation states of the complex exhibit single-molecule magnetic behaviors.

This paper describes charge transport by tunneling across self-assembled monolayers (SAMs) of thiolterminated derivatives of oligo(ethylene glycol) (HS(CH 2 CH 2 O) n CH 3 ; HS(EG) n CH 3 ); these SAMs are positioned between gold bottom electrodes and Ga 2 O 3 /EGaIn top electrodes and are of the form: SAMs of oligo(ethylene glycol)s using interactions among the high-energy, occupied orbitals associated with the lone-pair electrons on oxygen. According to calculations using density functional theory (DFT), these orbitals-localized orbitals predominately on the backbone oxygen atoms-are lower in energy (E MO = -6.8--7.2 eV), but more delocalized (due to interactions between orbitals on neighboring oxygen atoms), than the highest occupied molecular orbital (HOMO, E MO : ~-5.7 eV) localized on sulfur. Nonetheless, the existence of these high-energy, delocalized occupied orbitals, which are not present in analogous n-alkanethiols (E MO < -8.5 eV for orbitals associated with CH 2 ), rationalize the low value of β. SAMs of oligo(ethylene glycol)s (and of oligomers of glycine). SAMs based on S(EG) n CH 3 are, in this mechanism, good conductors (by hole tunneling), but good insulators (by electron and/or hole drift conduction)-an unexpected observation that suggests SAMs derived from these or electronically similar molecules as a new class of electronic materials. A second but less probable mechanism for this unexpectedly low value of β for SAMs of S(EG) n CH 3 rests on the 3 possibility of disorder in the SAM, and a systematic discrepancy between different estimates of the thickness of these SAMs.4

properties of SCO compounds is fundamental, to understand how they behave under electronic stimuli, especially when prepared as thin films. [8,9] Indeed, these molecules can be switched between two electronic states-termed high-spin (HS) and low-spin (LS)-with different magnetic, optical, and structural properties by the action of external stimuli (pressure, temperature, light-irradiation) [10][11][12][13][14] making them promising systems for new functional materials. [7] This is particularly important since the use of electrical stimuli to control (read/write) the spinstate of the system would provide a great advantage toward technological applications, compared to other conventional addressing methods such as light irradiation, and changes in temperature or pressure, that are less easily implemented. In this paper, we show that it is possible to design large area switchable molecular tunnel junctions, in which the switchable tunneling barrier is made of a thin film of a SCO compound. Those thin films, made by evaporation on TS Au (template-stripped gold), were thoroughly characterized using highly-sensitive and specific surface tools. Electrical switching has been studied as a function of temperature in a tunnel junction configuration, and the experimental results have been rationalized thanks to a theoretical model based on energy levels and electronic densities obtained at density functional theory (DFT) level. The good correlation we establish between experimental measurements and modeling proves the feasibility to design, manipulate, and read such ultrathin film devices, an important prerequisite for the development of future active multistable devices. The most critical issues toward the development of large-area spin-crossover based molecular junctions are i) to obtain high quality SCO thin films over large areas and ii) to have a measurement methodology that allows to measure their properties in an efficient and reliable manner. Moreover, to facilitate further developments and applications of those systems, it is highly desirable to have a transition temperature (and thus, possibly, a switching temperature) close to room temperature. For those reasons, we have chosen the [Fe(HB(trz) 3 ) 2 ] SCO complex, hereafter called 1 (HB(trz) 3 = tris(1H-1,2,4-triazol-1-yl)borohydride), [15][16][17][18] for which it was shown recently that it can be deposited as continuous thin films on surfaces by thermal evaporation. [19,20] Some recent efforts have focused on vertical large area SCO junctions with film thicknesses in the 10-200 nm range Thin films of a molecular spin crossover (SCO) Iron(II) complex featuring a high transition temperature are grown by sublimation in high vacuum on TS Au and investigated by X-ray and UV photoelectron spectroscopies. Temperaturedependent studies demonstrate that the thermally induced spin crossover behavior is preserved in thin films. A large-area ultrathin switchable spin crossover molecular vertical tunnel junction with top electrodes of the liquid eutectic of gallium and indium...

This work examines charge transport (CT) through self‐assembled monolayers (SAMs) of oligoglycines having an N‐terminal cysteine group that anchors the molecule to a gold substrate, and demonstrate that CT is rapid (relative to SAMs of n‐alkanethiolates). Comparisons of rates of charge transport‐using junctions with the structure AuTS/SAM//Ga2O3/EGaIn (across these SAMs of oligoglycines, and across SAMs of a number of structurally and electronically related molecules) established that rates of charge tunneling along SAMs of oligoglycines are comparable to that along SAMs of oligophenyl groups (of comparable length). The mechanism of tunneling in oligoglycines is compatible with superexchange, and involves interactions among high‐energy occupied orbitals in multiple, consecutive amide bonds, which may by separated by one to three methylene groups. This mechanistic conclusion is supported by density functional theory (DFT).

Dedicated to Jean-Pierre Sauvage on the occasion of his 65th birthday Single-molecule magnets (SMMs) are attractive because they present magnetic bistability of each isolated molecule, [1] thus enabling the discovery of a wide variety of intriguing phenomena and the possibility of preparing multifunctional molecular nanosystems.[2] The so-called double-decker lanthanide complexes of phthalocyanines, in which a lanthanide ion with a large total angular momentum is coordinated between two parallel phthalocyanine derivatives, are particularly attractive because of their relatively high blocking temperatures. [3][4][5] Our interest in these systems arose from the possibility of using organic synthesis to functionalize the SMM core. In particular, we have been engaged in a program aimed at preparing chiral SMMs which might show interesting chiroptical phenomena, [6,7] such as magnetochiral dichroism (MChD), which could be useful for data storage and processing.[8] To facilitate processing of SMMs and related materials, the incorporation of long alkyl chains is advantageous, and we were particularly attracted by liquid-crystalline phases, as previously carried out with a Mn 12 SMM [9] and spincrossover iron(II) compounds. [10] For this reason, we prepared compound 1, a chiral derivative of the double-decker terbium complex. It behaves both as a liquid crystal at room temperature and as a singlemolecule magnet at low temperatures. Importantly, when the material is cooled at different rates, the magnetic properties vary because of different degrees of supramolecular order. Herein we describe the preparation and characterization of this liquid-crystalline terbium double-decker phthalocyanine complex and how its mesomorphic properties can be used as a tool to adjust its magnetic properties reversibly at will. The terbium ion is used as a direct and very sensitive probe of the structural changes occurring at low temperatures, at which magnetic relaxation is dominated by direct tunneling transitions.The chiral metal-free (free-base) phthalocyanine 5, bearing eight identical stereocenters, was prepared in three steps from 4,5-dibromocatechol (Scheme 1) and the chiral bromoalkyl compound 2 derived from methyl lactate by a known procedure. [11] Compound 3 was converted into the bis(cyano) derivative 4 using zinc(II) cyanide, [12] and the purified compound was cyclized in n-hexanol using lithium metal to give 5. The corresponding terbium double-decker complex 1 was prepared by reacting 5 with anhydrous terbium chloride and lithium bis(trimethylsilyl)amide with minor changes from a published method.[13] The new compound was thoroughly purified by column chromatography, and was characterized by MALDI-TOF mass spectrometry, IR, UV/Vis absorption spectroscopy, circular dichroism spectroscopy, and elemental