π-Expanded Borazine: An Am bipolar Conjugated B-π-N Macrocycle

摘要

In reference to its isoelectronic and isostructural relationship with benzene, borazine is commonly referred to as "inorganic benzene".This concept has generated renewed interest in recent years, as the judicious replacement of C=C double bonds with isoelectronic and isosteric B-N fragments has resulted in a plethora of interesting molecules for applications ranging from hydrogen-storage materials to analogues of aromatic natural products, and new optical and electronic materials. For instance, introduction of a B-N fragment in benzene results in polarization of the molecule, which in turn leads to unusual reactivity, including nucleophilic substitution and hydrogenation under mild conditions.B-N function-alization of extended organic π-systems alters the electronic structure, resulting for example in low-lying LUMO levels and corresponding bathochromic shifts in the emission spectra.In the previous examples, B and N are directly connected. An alternative design has borane acceptor (A) moieties separated from amine donors (D) by an organic unconjugated linker. This D-π-A approach has proven successful for the development of nonlinear optical materials, ambipolar charge carriers in organic light emitting devices (OLEDs), and fluorescent anion sensors.