Marc Gingras

Turn-on Phosphorescence by Metal Coordination to a Multivalent Terpyridine Ligand: A New Paradigm for Luminescent Sensors

A hexathiobenzene molecule carrying six terpyridine (tpy) units at the periphery has been designed to couple the aggregation induced phosphorescence, displayed by the core in the solid state, to the metal binding properties of the tpy units. Upon Mg(2+) complexation in THF solution, phosphorescence of the hexathiobenzene core is turned on. Metal ion coordination yields the formation of a supramolecular polymer which hinders intramolecular rotations and motions of the core chromophore, thus favoring radiative deactivation of the luminescent excited state. Upon excitation of the [Mg(tpy)2](2+) units of the polymeric structure, sensitization of the core phosphorescence takes place with >90% efficiency. The light-harvesting polymeric antenna can be disassembled upon fluoride ion addition, thereby switching off luminescence and offering a new tool for fluoride ion sensing. This unique system can, thus, serve as cation or anion sensor.

Polysulfurated branched molecules containing functionalized m-phenylene sulfides

Polysulfurated branched molecules (dendrons) containing functionalized m-phenylene sulfide units were synthesized. An efficient way of making complex aromatic thiols from arylmethylthio groups is shown. A systematic study of the selectivity for producing a new series of phenylene sulfides was achieved. It has lead to the synthesis of rare dendrons containing sulfur and it will open the door to new poly(arylthio) dendrimers.

Synthesis of carbohelicenes and derivatives by 'carbenoid couplings'

Abstract Short synthetic sequences to carbohelicenes have been achieved under thermal conditions, without using photochemistry and high dilution. Couplings of aromatic bis(bromomethyl) moieties, in the presence of an excess of LiHMDS, are key reactions in the final ring closures to carbohelicenes. These optimized, quick and efficient reactions occur at 0°C within 10 min. and often provide [5]-helicene, [5]-helicene derivatives and [7]-helicene in ∼75% yield. Preliminary data questioned the formation of carbenoid anions and carbenes in the so called “carbenoid couplings”.

Syntheses of [5]-helicene by McMurry or carbenoid couplings

Abstract Short syntheses of [5]-helicene have been accomplished under thermal conditions, without using photochemistry and high dilution. Key reactions comprised a McMurry coupling of a dialdehyde or a carbenoid-type coupling of aromatic bis(bromomethyl) moieties. The last coupling provided a 7290 yield of [5]-helicene on a gram-scale (15 min., 0°C).

FUNCTIONALIZED P-PHENYLENE SULFIDES SYNTHESIS OF NEW MOLECULAR WIRES

Abstract Molecular wires containing p-phenylene sulfide units were synthesized. They could be used in material sciences and in supramolecular chemistry. Wires having 2 to 6 phenyl rings were functionalized at one end by an SH or SMe group, and at the other end, by an OH, OMe or OiPr groups. Formation of ArS bonds in the chain was achieved by Pd- or Cu-catalyzed couplings of aromatic thiols with aromatic halides. Conditions for a clean chemoselective deprotection of thiols from thiomethyl groups were developed.

A persulfurated benzene molecule exhibits outstanding phosphorescence in rigid environments: from computational study to organic nanocrystals and OLED applications

A molecule consisting of a hexathio-benzene core and peripheral tolyl substituents exhibits outstanding phosphorescence properties in some environments favoring rigidity, in the solid state and in a solid matrix at 77 K, while no luminescence is recorded in solution at room temperature. This peculiar behavior is attributed to the restriction of bond rotation and conformational mobility of the tolylthio substituents, which slows down the non-radiative deactivation processes of the phosphorescent excited state. The solid material (powder) shows a very high phosphorescence quantum yield (80%), which, to the best of our knowledge, is the highest reported value for organic molecules. The photophysical investigation was accompanied by a detailed computational study disclosing the role of CH–π interactions. This molecule has been exploited toward luminescent organic nanocrystals and light-emitting diodes with a fully solution processable technology.

Expeditive syntheses of functionalized pentahelicenes and NC-AFM on Ag(001).

One of the shortest and most efficient routes toward a series of functionalized pentahelicenes is reported. Benzylic (dibromo)methine coupling is an important entry into functional helicene chemistry. It allowed a mono- or a double functionalization by some metal-catalyzed Ar-C, Ar-S, Ar-CN, and Ar-I bond formations. Those functions offer new avenues for further applications. For instance, helicene (4) can be supported on a Ag(001) surface, which was characterized by high-resolution NC-AFM imaging.

Efficient formation of aromatic thiols from thiomethylated precursors

Abstract As a model study, a series of linear and branched p -phenylene and m -phenylene sulfides, functionalized by a thiomethyl group, were deprotected to thiols while using various alkyl thiolates at 160°C in DMF. Many complex aromatic thiols were obtained in almost quantitative yields from a trivial purification and without significant contamination by disulfides. This methodology is reliable, efficient and has been optimized on several substrates.

Gold nanoparticles prepared by laser ablation in aqueous biocompatible solutions: assessment of safety and biological identity for nanomedicine applications

Due to excellent biocompatibility, chemical stability, and promising optical properties, gold nanoparticles (Au-NPs) are the focus of research and applications in nanomedicine. Au-NPs prepared by laser ablation in aqueous biocompatible solutions present an essentially novel object that is unique in avoiding any residual toxic contaminant. This paper is conceived as the next step in development of laser-ablated Au-NPs for future in vivo applications. The aim of the study was to assess the safety, uptake, and biological behavior of laser-synthesized Au-NPs prepared in water or polymer solutions in human cell lines. Our results showed that laser ablation allows the obtaining of stable and monodisperse Au-NPs in water, polyethylene glycol, and dextran solutions. The three types of Au-NPs were internalized in human cell lines, as shown by transmission electron microscopy. Biocompatibility and safety of Au-NPs were demonstrated by analyzing cell survival and cell morphology. Furthermore, incubation of the three Au-NPs in serum-containing culture medium modified their physicochemical characteristics, such as the size and the charge. The composition of the protein corona adsorbed on Au-NPs was investigated by mass spectrometry. Regarding composition of complement C3 proteins and apolipoproteins, Au-NPs prepared in dextran solution appeared as a promising drug carrier. Altogether, our results revealed the safety of laser-ablated Au-NPs in human cell lines and support their use for theranostic applications.

Two-dimensional nanostructured growth of nanoclusters and molecules on insulating surfaces.

Noncontact atomic force microscopy (nc-AFM), Kelvin probe force microscopy (KPFM) and first principle calculations show that the nanostructured (001) Suzuki surface of Cd(2+) doped NaCl can be used to confine the growth of palladium clusters and functionalized brominated pentahelicene molecules into only the Suzuki regions, which contain the impurities. The Suzuki surface is an ideal model surface for nanostructuring metal clusters and molecules.