Synthesis of O-Alkyl D-Xylitols with Potential Luquid-Crystalline Properties 1

Abstract

A general synthetic approach to enantiomerically pure x-O-alkyl-D-xylitols has been developed from D-xylose. These products provide access to new thermotropic liquid crystals.

     

6,12-Diarylindeno[1,2-b]fluorenes: syntheses, photophysics, and ambipolar OFETs

Herein we report the synthesis and characterization of a series of 6,12-diarylindeno[1,2-b]fluorenes (IFs). Functionalization with electron donor and acceptor groups influences the ability of the IF scaffold to undergo two-electron oxidation and reduction to yield the corresponding 18- and 22-π-electron species, respectively. A single crystal of the pentafluorophenyl-substituted IF can serve as an active layer in an organic field-effect transistor (OFET). The important finding is that the single-crystal OFET yields an ambipolar device that is able to transport holes and electrons.     

Synthesis,Structural Characterization,Photophysics, and Broadband Nonlinear Absorption of a Platinum(II) Complex with the 6‐(7‐Benzothiazol‐2′‐yl‐9,9‐diethyl‐9 H‐fluoren‐2‐yl)‐2,2′‐bipyridinyl Ligand

A platinum complex with the 6‐(7‐benzothiazol‐2′‐yl‐9,9‐diethyl‐9H‐fluoren‐2‐yl)‐2,2′‐bipyridinyl ligand ( 1 ) was synthesized and the crystal structure was determined. UV/Vis absorption, emission, and transient difference absorption of 1 were systematically investigated. DFT calculations were carried out on 1 to characterize the electronic ground state and aid in the understanding of the nature of low‐lying excited electronic states. Complex 1 exhibits intense structured ¹π–π* absorption at λ_abs<440 nm, and a broad, moderate ¹M LCT/¹LLCT transition at 440–520 nm in CH₂Cl₂ solution. A structured ³π–π*/³M LCT emission at about 590 nm was observed at room temperature and at 77 K. Complex 1 exhibits both singlet and triplet excited‐state absorption from 450 nm to 750 nm, which are tentatively attributed to the ¹π–π* and ³π–π* excited states of the 6‐(7‐benzothiazol‐2′‐yl‐9,9‐diethyl‐9H‐fluoren‐2‐yl)‐2,2′‐bipyridine ligand, respectively. Z‐scan experiments were conducted by using ns and ps pulses at 532 nm, and ps pulses at a variety of visible and near‐IR wavelengths. The experimental data were fitted by a five‐level model by using the excited‐state parameters obtained from the photophysical study to deduce the effective singlet and triplet excited‐state absorption cross sections in the visible spectral region and the effective two‐photon absorption cross sections in the near‐IR region. Our results demonstrate that 1 possesses large ratios of excited‐state absorption cross sections relative to that of the ground‐state in the visible spectral region; this results in a remarkable degree of reverse saturable absorption from 1 in CH₂Cl₂ solution illuminated by ns laser pulses at 532 nm. The two‐photon absorption cross sections in the near‐IR region for 1 are among the largest values reported for platinum complexes. Therefore, 1 is an excellent, broadband, nonlinear absorbing material that exhibits strong reverse saturable absorption in the visible spectral region and large two‐photon‐assisted excited‐state absorption in the near‐IR region.     

Diazaheterocycle analogues of tetracene: synthesis and properties of a naphtho-fused cinnoline and a naphtho-fused isoindazole

The synthesis and characterization of a diethynyl naphtho-fused cinnoline and isoindazole are described. The results show that both electron-accepting and electron-donating molecules can be prepared from a common intermediate.     

Synthesis of 2H-indazoles via Lewis acid promoted cyclization of 2-(phenylazo)benzonitriles

Lewis-acid promoted "coarctate" cyclization of 10 2-(phenylazo)benzonitrile derivatives furnishes the isoindazole ring system in ca. 65-95% yield. A plausible mechanism for this unusual transformation is proposed.     

Building symmetric two-dimensional two-photon materials

Two-dimensional multi-annulenic carbon networks are important molecules with possible applications in optoelectronic devices and nonlinear optics. Investigations of two-photon absorption (TPA) cross sections have been carried out in a series of annulenes with a basic building block approach and variable symmetries. Enhancement of the TPA cross section has been observed with an increase in number of building blocks and order of symmetry. Evaluations of the ground-state transition dipole moment and chromophore density are not sufficient to explain the observed enhancement. Estimates of excited-state transition dipole moments made by femtosecond transient absorption measurements are able to successfully predict the observed trend in TPA cross section. It has been observed that the symmetry of the molecule plays a vital role in enhancing the TPA cross section by virtue of increasing the excited-state transition dipole moment.     

Sur quelques récents résultats dans la théorie des surfaces algébriques

Sans résumé     

Colorimetric metal ion binding of catechol-based coatings inspired by melanin and molecular imprinting

Catechol-containing biomolecules and related synthetic materials are of interest for a broad range of applications. Our group has been interested in the potential of eumelanin, a catechol-containing biomaterial and the black-to-brown pigment in humans, and synthetic eumelanin analogues for water purification applications. In an attempt to apply the strategy of molecular imprinting towards lead-binding synthetic eumelanin coatings, we developed a PbO₂-mediated synthesis that was subsequently tested with a number of catechols in addition to the eumelanin and polydopamine monomers l-dopa and dopamine. Although this strategy did not provide significant improvements in affinity or selectivity, we found that the PbO₂-mediated oxidative polymerisation of 1,2-dihydroxybenzene generates a coating that darkens visibly upon binding Pb²⁺ and other metal ions. Oxidative polymerisation of catechol with sodium periodate also yields a coating with this colorimetric response. Of eight metal ions tested, the coatings are most responsive to Pb²⁺ and Cu²⁺, as analysed by quantitative colorimetry. With further optimisation, these coatings could prove useful for the colorimetric sensing of metal ions.