Reversible Redox Switching of Chromophoric Phenylmethylenepyrans by Carbon-Carbon Bond Making/Breaking.

Electrochromic organic systems that can undergo substantial variation of their optical properties upon electron stimulus are of high interest for the development of functional materials. In particular, devices based on radical dimerization are appropriate because of the effectiveness and speed of carbon-carbon bond making/breaking. Phenylmethylenepyrans are organic chromophores which are well suited for such purposes since their oxidation leads to the reversible formation of bispyrylium species by radical dimerization. In this paper, we show that the redox and spectroscopic properties of phenylmethylenepyrans can be modulated by adequate variation of the substituting group on the para position of the phenyl moiety, as supported by DFT calculations. This redox switching is reversible over several cycles and is accompanied by a significant modification of the UV-vis spectrum of the chromophore, as shown by time-resolved spectroelectrochemistry in thin-layer conditions.

Porosity-driven large amplitude dynamics for nitroaromatic sensing with fluorescent films of alternating D-π-A molecules.

We report herein the structural properties and nitroaromatic sensing performances of fluorescent thin films formed by alternating donor-acceptor π-conjugated chromophores. The incorporation of a flexible one-dimensional alkyl chain in the chromophore backbone drastically accelerates by more than one order of magnitude the sensing dynamics for the detection of 2,4-dinitrotoluene (DNT) vapors.

Reaction of BH4- with [Mo2Cp2(mu-SMe)n] species to give tetrahydroborato, hydrido or dimetallaborane compounds: control of product by ancillary ligands.

The reaction of mono- or dichloro-dimolybdenum(III) complexes [Mo2Cp2(mu-SMe)2(mu-Cl)(mu-Y)] (Cp=eta5-C5H5; 1, Y=SMe; 2, Y=PPh2; 3, Y=Cl) with NaBH4 at room temperature gave in high yields tetrahydroborato (8), hydrido (9) or metallaborane (12) complexes depending on the ancillary ligands. The correct formulation of derivatives and has been unambigously determined by X-ray diffraction methods. That of the hydrido compound 9 has been established in solution by NMR analysis and confirmed by an X-ray study of the mu-azavinylidene derivative [Mo2Cp2(mu-SMe)2(mu-PPh2)(mu-N=CHMe)] (10) obtained from the insertion of acetonitrile into the Mo-H bond of 9. Reaction of NaBH4 with nitrile derivatives, [Mo2Cp2(mu-SMe)4-n(CH3CN)2n]n+(5, n=1; 6 n=2), afforded the tetrahydroborato compound 8, together with a mu-azavinylidene species [Mo2Cp2(mu-SMe)3(mu-N=CHMe)](14), when n=1, and the metallaborane complex 12, together with a mixed borohydrato-azavinylidene derivative [Mo2Cp2(mu-SMe)2(mu-BH4)(mu-N=CHMe)] (13), when n=2. The molecular structures of these complexes have been confirmed by X-ray analysis. Preparations of some of the starting complexes (3 and 4) are also described, as are the molecular structures of the precursors [Mo2Cp2(mu-SMe)2(mu-X)(mu-Y)] (1, X/Y=Cl/SMe; 2, X/Y=Cl/PPh2; 4, X/Y=SMe/PPh2).