Photochemistry Highlights on On-Surface Synthesis.

On-surface chemistry is a promising way to achieve the bottom-up construction of covalently-bonded molecular precursors into extended atomically-precise polymers adsorbed on surfaces. These polymers exhibit unprecedented physical or chemical properties which are of great interest for various potential applications. These nanostructures were mainly obtained in ultra-high vacuum (UHV) on noble metal single-crystal surfaces by thermal annealing as stimulus to provoke the polymerization with a catalytic role of the surface adatoms. Nevertheless, photons are also a powerful source of energy to induce the formation of covalent architectures, even if it is less-used on surfaces than in solution. In this minireview, we discuss the photo-induced on-surface polymerization from the basic mechanisms of photochemistry to the formation of extended polymers on different kinds of surfaces, which are characterized by scanning probe microscopies.

Controlled growth of a bicomponent supramolecular network by the sergeants & soldiers principle.

The co-deposition of 1,4-di(4',4''-pyridyl)benzene and 1,4-di(4',4''-bromophenyl)benzene on Si(111)-B surface leads to the formation of a highly regular self-assembly. The formation of this network has been investigated by STM and has been elucidated in the light of sergeants & soldiers principle due to halogen bonding on a silicon surface.

Extended monolayer of cyano-ended oligo(para-phenylenes) at the air/HOPG interface investigated by high-resolution AFM.

The formation of functional networks on surfaces is one of the main challenges in the field of nanotechnologies. In this paper, we shall propose a very simple process which can be used to achieve the formation of extended monolayer of functional oligo(para-phenylenes) molecules at the air/graphite interface. By developing a convergent strategy, we successfully achieved the synthesis of oligo(para-phenylenes) molecules with a tuneable length. The photophysical properties of these new oligomers were characterized by UV-vis absorption and fluorescence spectroscopy. Deposition of these molecules by a simple spin-coating process on a highly oriented pyrolytic graphite (HOPG) surface leads to the formation of extended monolayered 2D networks. These networks were characterized by atomic force microscopy experiments under ambient conditions with submolecular resolution thus providing the adsorption model of these molecules on an HOPG surface.

Supramolecular self-assembly of brominated molecules on a silicon surface.

Hydrogen and halogen bonds have been associated for the growth of 2D compact supramolecular networks on a silicon surface. These interactions have been elucidated in a complete monolayer of a 4,4''-dibromo-p-terphenyl (DBT) molecule on a Si(111)-B surface by combining scanning tunneling microscopy (STM) and density functional theory (DFT) calculations.

Anisotropic growth of the thiophene-based layer on Si(111)-B.

The formation of large assemblies on the Si(111)-B surface is discussed with the help of STM simulations and DFT calculations. Although highly regular assemblies of DTB10B along the Si row direction are observed, the existence of two herringbone isomers introduces a lower periodicity within the 2D molecular network. The formation of herringbone units is explained by weak intermolecular interactions while the 1D assembling depends mainly on the interactions of the C10 side chains with the Si(111)-B surface.

Nondestructive room-temperature adsorption of 2,4,6-tri(2'-thienyl)-1,3,5-triazine on a Si-B interface: high-resolution STM imaging and molecular modeling.

Organic nanostructures on semiconductors are currently investigated but the surfaces are known to interact strongly with molecules. To reduce the molecule-surface interaction, we used the Si(111)-B square root 3 x square root 3R30 degrees . Deposition of isolated 2,4,6-tri(2'-thienyl)-1,3,5-triazine, was achieved at room temperature without modification of their pi skeleton. This fascinating arrangement, observed by STM, has been validated by full density functional theory computations onto the entire system. The theoretical results give a clear explanation for the specific adsorption sites of molecules on the substrate.

Action of low frequency vibration on liquid droplets and particles.

Liquids handling is an important issue in biomedical analysis. Two different devices for acoustic manipulation of droplets have already been tested. The first one, more classical, uses a high frequency travelling wave and acoustic streaming. The second one uses low frequency flexural standing waves in a plate. This means of liquid handling is original and easy to implement but the physical principle is not obvious. In order to understand more precisely the phenomena involved we present new observations on droplet displacement between two planes and on the behaviour of a droplet on an inclined vibrating plane with this method. The physical principle involved is discussed. The common acoustic radiation pressure formulation is expressed via the non-linear theory of sound propagation, but in our case the acoustic wavelength is much smaller than the height of a water droplet. To get a better understanding of the phenomenon, further experiments on the internal liquid flow and behaviour of particles in the droplet have been performed. These will be compared with results obtained with particles in a thin water-filled vibrating glass tube. The general conclusion is that the phenomenon is practical to use for droplet displacement even if its complex mechanism is not completely understood.