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Synthesis, structure and electrochemistry of thiopene-containing oligoacenes and metallated schiff base monomers Pietrangelo, Agostino

Abstract

The syntheses, structures, and electrochemistry of novel thiophene-containing oligoacenes and metallated Schiff base monomers are reported. Bent anthradithiophenes (67-71) were prepared by the oxidative photocyclization of 1 ,4-dithienyl-2,5-divinylbenzenes (62-66) and their structural, spectroscopic, and electrochemical properties determined by x-ray crystallography, powder x-ray diffraction, cyclic voltammetry, and UV/vis absorption and fluorescence spectroscopies. The site-selective reactivity of the thiophene moieties enabled access to the diphenyl- and dialkyl-functionalized derivatives where the substituents significantly influence the solid-state packing order of the oligoacenes in single crystals and as thermally evaporated films. Cyclic voltammetry studies suggest that the parent 67 electrochemically polymerizes via an oxidative coupling mechanism through the thienyl c carbons affording a poly-oligoacene polymer, a feature that was not observed in the functionalized derivatives. Thiophene-containing metallated Schiff base monomers were electrochemically polymerized on Earth (1 g) and in microgravity (0 g) and the microscopic order of the subsequent polymer films probed by measuring the magnitude of the third-order nonlinear optical susceptibility tensor X (³). The metallated polymers grown under terrestrial conditions possess lower X (³) values than those grown in microgravity where gravity induced convection currents are suppressed, suggesting that buoyancy forces generated under terrestrial conditions disrupt the weak intermolecular interactions between polymer chains that ultimately give rise to improved microscopic order. Moreover, the X (³) enhancements were found to vary between Cu²⁺ polymers grown in microgravity that differed only in the length of the peripheral alkoxy substituents indicating that in addition to the metal centres, the length of the alkoxy substituent also influences the microscopic order of the polymer films. A series of Pd-containing oligothiophenes were electrochemically polymerized onto carbon fiber electrodes and their catalytic activity investigated through a variety of C-C cross-coupling reactions. The polymers possessed the same catalytically active Pd-sites but differed in their connectivity to the polythiophene backbone, a factor that influenced their electrochemistry and film quality. Poly-100 proved to be an efficient catalyst for intra- and intermolecular C-C crosscoupling reactions (i.e., Suzuki, Heck, Sonogashira). X-ray photoelectron spectroscopy and control experiments suggest that polymer and metal ion-leaching is negligible during the course of the reactions, proving that poly-100 is a heterogeneous catalyst.

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