Self-Assembly of TbPc2 Single-Molecule Magnets on Surface through Multiple Hydrogen Bonding.

The complexation between 2-ureido-4[1H]-pyrimidinone (UPy) and 2,7-diamido-1,8-naphthyridine (NaPy) is used to promote the mild chemisorption of a UPy-functionalized terbium(III) double decker system on a silicon surface. The adopted strategy allows the single-molecule magnet behavior of the system to be maintained unaltered on the surface.

Exclusive recognition of sarcosine in water and urine by a cavitand-functionalized silicon surface.

A supramolecular approach for the specific detection of sarcosine, recently linked to the occurrence of aggressive prostate cancer forms, has been developed. A hybrid active surface was prepared by the covalent anchoring on Si substrates of a tetraphosphonate cavitand as supramolecular receptor and it was proven able to recognize sarcosine from its nonmethylated precursor, glycine, in water and urine. The entire complexation process has been investigated in the solid state, in solution, and at the solid-liquid interface to determine and weight all the factors responsible of the observed specificity. The final outcome is a Si-based active surface capable of binding exclusively sarcosine. The complete selectivity of the cavitand-decorated surface under these stringent conditions represents a critical step forward in the use of these materials for the specific detection of sarcosine and related metabolites in biological fluids.

Cavitand-grafted silicon microcantilevers as a universal probe for illicit and designer drugs in water.

The direct, clean, and unbiased transduction of molecular recognition into a readable and reproducible response is the biggest challenge associated to the use of synthetic receptors in sensing. All possible solutions demand the mastering of molecular recognition at the solid-liquid interface as prerequisite. The socially relevant issue of screening amine-based illicit and designer drugs is addressed by nanomechanical recognition at the silicon-water interface. The methylamino moieties of different drugs are all first recognized by a single cavitand receptor through a synergistic set of weak interactions. The peculiar recognition ability of the cavitand is then transferred with high fidelity and robustness on silicon microcantilevers and harnessed to realize a nanomechanical device for label-free detection of these drugs in water.

Cavitand-functionalized porous silicon as an active surface for organophosphorus vapor detection.

This paper reports on the preparation of a porous silicon-based material covalently functionalized with cavitand receptors suited for the detection of organophosphorus vapors. Two different isomeric cavitands, both containing one acid group at the upper rim, specifically designed for covalent anchoring on silicon, were grafted on H-terminated porous silicon (PSi) by thermal hydrosilylation. The covalently functionalized surfaces and their complexation properties were characterized by combining different analytical techniques, namely X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and mass spectroscopy analysis coupled with thermal desorption experiments. Complexation experiments were performed by exposing both active surfaces and a control surface consisting of PSi functionalized with a structurally similar but inactive methylene-bridged cavitand (MeCav) to dimethyl methylphosphonate (DMMP) vapors. Comparison between active and inactive surfaces demonstrated the recognition properties of the new surfaces. Finally, the nature of the involved interactions, the energetic differences between active and inactive surfaces toward DMMP complexation, and the comparison with a true nerve gas agent (sarin) were studied by DFT modeling. The results revealed the successful grafting reaction, the specific host-guest interactions of the PSi-bonded receptors, and the reversibility of the guest complexation.

Cavitand-Decorated Silicon Columnar Nanostructures for the Surface Recognition of Volatile Nitroaromatic Compounds.

Nanocolumnar Si substrates (porous silicon (PSi)) have been functionalized with a quinoxaline-bridged (EtQxBox) cavitand in which the quinoxaline moieties are bonded to each other through four ethylendioxy bridges at the upper rim of the cavity. The receptor, which is known to selectively complex aromatic volatile organic compounds (VOCs) even in the presence of aliphatic compounds, has been covalently anchored to PSi. The larger surface area of PSi, compared to that of flat substrates, allowed one to study the recognition process of the surface-grafted receptors through different techniques: Fourier-transform infrared spectroscopy, thermal desorption, and X-ray photoelectron spectroscopy. The experiments proved that surface-grafted cavitands retain the recognition capability toward aromatic VOCs. In addition, the affinities of EtQxBox for various aromatic compounds (i.e., benzene, toluene, nitrobenzene, and p-nitrotoluene) have been studied combining density functional theory computations and thermal desorption experiments. Computational data based on the crystal structures of the complexes indicate that this cavitand possesses a higher affinity toward aromatic nitro-compounds compared to benzene and toluene, making this receptor of particular interest for the detection of explosive taggants. The results of computational studies have been validated also for the surface-grafted receptor through competitive recognition experiments. These experiments showed that EtQxBox-functionalized PSi can recognize nitrobenzene in the presence of a significant excess of aromatic vapors such as benzene (1:300) or toluene (1:100).

In situ metalation of free base phthalocyanine covalently bonded to silicon surfaces.

Free 4-undecenoxyphthalocyanine molecules were covalently bonded to Si(100) and porous silicon through thermic hydrosilylation of the terminal double bonds of the undecenyl chains. The success of the anchoring strategy on both surfaces was demonstrated by the combination of X-ray photoelectron spectroscopy with control experiments performed adopting the commercially available 2,3,9,10,16,17,23,24-octakis(octyloxy)-29H,31H-phthalocyanine, which is not suited for silicon anchoring. Moreover, the study of the shape of the XPS N 1s band gave relevant information on the interactions occurring between the anchored molecules and the substrates. The spectra suggest that the phthalocyanine ring interacts significantly with the flat Si surface, whilst ring-surface interactions are less relevant on porous Si. The surface-bonded molecules were then metalated in situ with Co by using wet chemistry. The efficiency of the metalation process was evaluated by XPS measurements and, in particular, on porous silicon, the complexation of cobalt was confirmed by the disappearance in the FTIR spectra of the band at 3290 cm(-1) due to -NH stretches. Finally, XPS results revealed that the different surface-phthalocyanine interactions observed for flat and porous substrates affect the efficiency of the in situ metalation process.

Enantioselective extraction mediated by a chiral cavitand-salen covalently assembled on a porous silicon surface.

A chiral organic-inorganic hybrid material, based on a porous silicon surface functionalized with a chiral cavitand, was designed and synthesized. The affinity of this device in water toward a bromine-marked alkyl-ammonium salt has been evaluated using XPS detection. UV and CD measurements highlight the enantioselective extraction from a racemic mixture in water of the S-enantiomer of the selected guest (ee ≥ 80%).

Magnetic behaviour of TbPc2 single-molecule magnets chemically grafted on silicon surface.

Single-molecule magnets (SMMs) are among the most promising molecular systems for the development of novel molecular electronics based on spin transport. Going beyond investigations focused on physisorbed SMMs, in this work the robust grafting of terbium(III) bis(phthalocyaninato) complexes to a silicon surface from a diluted solution is achieved by rational chemical design yielding the formation of a partially oriented monolayer on the conducting substrate. Here by exploiting the surface sensitivity of X-ray circular magnetic dichroism, we evidence an enhancement of the magnetic bistability of this SMM, in contrast to the dramatic reduction of the magnetic hysteresis that characterizes monolayer deposits evaporated on noble and ferromagnetic metals. Photoelectron spectroscopy investigations and density functional theory analysis suggest a non-innocent role played by the silicon substrate, evidencing the potentiality of this approach for robust integration of bistable magnetic molecules in electronic devices.

Micro- and nanoscale electrical characterization of large-area graphene transferred to functional substrates.

Chemical vapour deposition (CVD) on catalytic metals is one of main approaches for high-quality graphene growth over large areas. However, a subsequent transfer step to an insulating substrate is required in order to use the graphene for electronic applications. This step can severely affect both the structural integrity and the electronic properties of the graphene membrane. In this paper, we investigated the morphological and electrical properties of CVD graphene transferred onto SiO2 and on a polymeric substrate (poly(ethylene-2,6-naphthalene dicarboxylate), briefly PEN), suitable for microelectronics and flexible electronics applications, respectively. The electrical properties (sheet resistance, mobility, carrier density) of the transferred graphene as well as the specific contact resistance of metal contacts onto graphene were investigated by using properly designed test patterns. While a sheet resistance R sh ≈ 1.7 kΩ/sq and a specific contact resistance ρc ≈ 15 kΩ·µm have been measured for graphene transferred onto SiO2, about 2.3× higher R sh and about 8× higher ρc values were obtained for graphene on PEN. High-resolution current mapping by torsion resonant conductive atomic force microscopy (TRCAFM) provided an insight into the nanoscale mechanisms responsible for the very high ρc in the case of graphene on PEN, showing a ca. 10× smaller "effective" area for current injection than in the case of graphene on SiO2.