Fabio Lupo

Self-Propagating Assembly of a Molecular-Based Multilayer

Accelerated growth of a molecular-based material that is an active participant in its continuing self-propagated assembly has been demonstrated. This nonlinear growth process involves diffusion of palladium into a network consisting of metal-based chromophores linked via palladium.

Linear vs Exponential Formation of Molecular-Based Assemblies

Here we present the critical role of the molecular structure and reaction parameters on the nature of thin-film growth, using a versatile two-step assembly method with organic and metal-organic chromophores cross-linked with palladium. It was found that the polypyridyl complexes exhibit exponential growth, whereas, under identical conditions, the organic systems exhibit linear behavior. The internal film morphology plays a pivotal role in the storage and usage of the palladium, where a more porous structure results in exponential growth. Interestingly, through proper tuning of the reaction conditions, the growth of the molecular assemblies can be controlled, resulting in a changeover from exponential to linear growth. These findings unequivocally demonstrate the importance of both the internal film structure and deposition conditions on the assembly of molecular-based films.

Tunable luminescent properties of a europium complex monolayer

Silica substrates were functionalized with a covalent 4-ClCH2C6H4SiCl3 monolayer. Additional covalent bonding of the tris(dibenzoylmethane) mono(5-amino-1,10-phenanthroline)europium (III) to the silylated substrates was further achieved. The optical properties of this robust monolayer system were studied at room temperature by both UV-vis and photoluminescence measurements. The UV-vis spectrum, in tune with solution measurements, reveals the presence of the title compound on the film surface. The surface chemical characterization of the monolayer was carried out by X-ray photoelectron measurements and the Eu spectrum shows spin–orbit components of the Eu 3d states. Photoluminescence measurements indicate the presence of two bands at 591 and 614 nm whose intensities can be switched by different light inputs. The adopted synthetic procedure has proven to be effective in transferring molecular properties to a solid state device.

Au–Ag/CeO2 and Au–Cu/CeO2 Catalysts for Volatile Organic Compounds Oxidation and CO Preferential Oxidation

Oxidation of volatile organic compounds (VOC) and preferential oxidation of CO in the excess of H2 (CO-PROX) were investigated over mono and bimetallic Au–Ag/CeO2 and Au–Cu/CeO2 catalysts. For the oxidation of VOC (2-propanol, ethanol and toluene) Au/CeO2 was the most active catalyst for the combustion of alcohols to CO2, Ag/CeO2 gave the best performance in the toluene total oxidation, Au–Ag/CeO2 and Au–Cu/CeO2 showed the highest selectivity to partial oxidation products. For CO-PROX Au–Ag/CeO2 and Au–Cu/CeO2 samples exhibited higher CO2 yield at low temperature than monometallic ones. The improved performance of bimetallic catalysts were accounted for an enhancement of surface ceria oxygens mobility caused by the addition of Ag or Cu to Au/CeO2 and involved in both investigated reactions. This effect was more evident on Au–Ag/CeO2 where a strong Au–Ag interaction occurred with formation of Au–Ag alloy or linked monometallic nanoparticles.Graphical Abstract

Assembly of Surface-Confined Homochiral Helicates: Chiral Discrimination of DOPA and Unidirectional Charge Transfer

Surface-confined double-helical polymers are generated by dynamic covalent assembly with preservation of chirality, metal coordination environment, and oxidation state of the precursor complexes. This one-step procedure involves both in solution and solution-to-surface assembly and resulted in chiral interfaces where pairs of ligands are wrapped around arrays of metal ions. In-plane XRD experiments revealed the formation of a highly ordered structure along the substrate surface. The chirality of the surfaces is expressed by the selective recognition of 3,4-dihydroxyphenylalanine (DOPA). The CD measurements show a response of the Δ-polymer-modified quartz substrates toward D-DOPA, whereas no change was observed after treatment with L-DOPA. These coordination-based interfaces assembled on metal-oxide substrates in combination with a redox-probe, [Os(bpy)3](PF6)2, in solution can resemble the behavior of a rectifier.

Reversible photoswitching of stimuli-responsive Si(100) surfaces engineered with an assembled 1 -cyano-1-phenyl-2-[4/-(10-undecenyloxy)phenyl]-ethylene monolayer

Si(100) surfaces were molecularly engineered by covalent linkage of a monolayer of two stilbene-based chromophores, either 1-cyano-1-phenyl-2-[4′-(10-undecenyloxy)phenyl]-ethylene or its chlorine derivative, 1-cyano-1-(4-Cl-phenyl)-2-[4′-(10-undecenyloxy)phenyl]-ethylene. The hybrid systems have been probed by monochromatized angle-resolved X-ray photoelectron spectroscopy (AR-XPS) and atomic force microscopy (AFM) measurements. Results indicated robust covalent linkage of stilbene molecules to the functionalized substrate surfaces. AFM lithography and contact angle (CA) analysis confirmed that the adopted molecular architectures proved to be well-suited for reversible cis–trans photoswitching promoted by UV irradiation in the solid state.

A surface-confined OMnV(salen) oxene catalyst and high turnover values in asymmetric epoxidation of unfunctionalized olefins

Given the widespread importance of chiral epoxides in chemical, biochemical and agricultural fields, an efficient synthesis that avoids wasteful use of the catalyst and assures its total recovery and reuse and high turnover values is highly desirable. We report on a thermally and temporally robust covalent monolayer of (salen)Mn(III) molecules on silica functionalized substrates that resulted in an active heterogeneous catalyst for enantioselective epoxidation of 6-ciano-2,2-dimethyl-chromene, chosen as a model alkene, in high yields and high turnover numbers. No catalyst leaching was observed thus allowing continuous recycling. Experimental XPS evidence for the formation of the surface confined OMnV(salen) oxene species has been obtained.

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

Summary 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.