| Abstract
| - The bifunctional conjugated organoboranes Ar2BbtBAr2, which contain 2,2‘-bithiophene (bt)linkers and different aryl substituents on boron (3: Ar = p-tBuC6H4; 4: Ar = C6F5; 5: Ar = C6F5, Fc; Fc =ferrocenyl), have been synthesized. The electronic communication between the boron centers andcooperativity effects in the binding of pyridine have been investigated by a comprehensive study usingX-ray crystallography, DFT calculations, cyclic voltammetry, 1H and 19F NMR, and UV visible absorptionand emission spectroscopy. A comparison of the single-crystal X-ray structures of 4 and 4Py2 revealed astrongly diminished bond alternation in the thiophene rings for 4, indicative of a high degree of electronicdelocalization. DFT calculations are in good agreement with the structural features determined from theX-ray analysis and, consistent with the experimental absorption and emission data, predict a smaller HOMO−LUMO gap for green luminescent 4 in comparison to blue luminescent 3. The complexation of pyridine tothe two boron centers was further investigated by 1H and 19F NMR for 4 and by 1H NMR and UV−visibleabsorption spectroscopy for 3. We found that binding of the first pyridine molecule to one of the borylgroups significantly lowers the Lewis acidity of the other boryl group. For 3, the interaction parameter a,which provides a measure of communication between the boron sites, was determined to be a = 0.23 byUV−visible titration and 0.21 by 1H NMR spectroscopy. Further enhanced electronic communication wasobserved for the more highly Lewis acidic fluorinated derivative 4, for which a = 0.025 according to 19Fand 1H NMR spectroscopy.
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