Novel alkali cation chemosensors based on n-9-anthrylaza-crown ethers

[structure: see text] A novel alkali cation selective probe is described which exhibits unique ICT and binding properties, allowing the ratiometric titration of sodium cations in the presence of other alkali metal ions.     

Polar‐Solvent Effect on the Photocycloisomerization of Symmetrical Bis[anthracenes]: A Transient Ultrafast Kinetic Study

Bis[anthracenes] are the few among the fluorescing nonconjugated bichromophores that possess photoreactive properties. The 9,9′‐[methylenebis(oxy)]bis[anthracenes] 1 (AOCH₂OA) exhibit the highest known intramolecular photocycloaddition quantum yield from the S₁ state and, moreover, display a higher yield in polar solvents, an unexpected result for symmetrical systems. No excimer fluorescence was detected in solution at room temperature. The 10,10′‐dimethoxy derivative 1b was studied by picosecond (ps) laser spectroscopy. In nonpolar solvents (methylcyclohexane), S_n←S₁ was the only transient absorption detected, whereas, in polar solvents (MeCN), the growth and the decay of a second transient were recorded, and the second transient was attributed to a zwitterion A^+.−A^−.. The kinetics data were derived, and it was concluded that electron transfer and ion recombination should be at the origin of the observed rate enhancement of cycloadduct formation in polar solvents.     

Structural variations in a family of orthodialkoxyarenes organogelators

A series of low mass organic gelators (LMOGS) 1 to 6 whose chemical structures have in common an orthodialkoxyarene feature was prepared in order to compare the shape of their fibrillar network as investigated by small-angle neutron scattering (SANS) experiments. All members of the family exhibit a pronounced tendency to bundle formation by merging isolated fibers in extended packets of average diameter >500 A. Variations of the 2D packing symmetry are observed from hexagonal to square orderings with close derivatives of the reference member 2,3-didecyloxyanthracene (DDOA). Networks in which the fraction of isolated fibers is significant enough to allow for their SANS identification are those for 6,7-dichloro-2,3-didecyloxyanthracene (Cl(2)DDOA) and 2,3-dodecyloxy-9,10-anthraquinone (5). For this latter, the monodispersity of the cross-sections (thickness=74 A) is remarkable and the rectangular shape (b/a approximately 0.12) accounts for a merging mechanism into anisotropic bundles (ribbons).     

Self-assembly of soluble anthracene, tetracene and pentacene derivatives

New soluble disubstituted acenes (tetracene, pentacene) have been designed in order to mimic 2,3-alkoxy derivatives of anthracene. They have been shown to self-assemble and gellify a large variety of organic solvents. This process involves the formation of nano-fibres through non-covalent molecular interactions (van der Waals, π-π stacking), weaving a three-dimensional supramolecular network. Efficient transfer of excitation energy through these nano-structures has been evidenced in an anthracene light-harvesting matrix doped with less than 1 mol% of a tetracene energy trap.     

Study of structural and electronic transport properties of Ce-doped LaMnO3

The structural and electronic transport properties of La_1−x Ce _x MnO₃ (x=0.0–1.0) have been studied. All the samples exhibit orthorhombic crystal symmetry and the unit cell volume decreases with Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration up to 50% doping. The system La_0.5Ce_0.5MnO₃ also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition.     

Study of non-conjugated bichromophores linked by a polyether chain. Kinetic analysis of the formation of intramolecular excimers and photocyclomerization of some bisanthracenes

Dynamic properties of polyoyethylene chains are evaluated by the determination of rate constants (k_DM) of intramolecular excimer formation for four bis(9-anthryloxy)polyoxaalkanes in benzene and ethanol. The Kinetic parameters for the photodimenzation process of these compounds have been determined.