Luminescent Symmetrically and Unsymmetrically Substituted Diboranes(4)

Abstract

A series of 4‐(dimethylamino)phenyl and pentafluorophenyl‐substituted 1,2‐bis(dimethylamino)diboranes(4) of type A, benzo‐fused cyclic 1,4‐diaza‐2,3‐diborinanes of type B, and 1,2‐diduryldiboranes(4) of type C were synthesized and structurally characterized. Spectroscopic studies revealed that the substitution pattern is a decisive factor for the observation of fluorescence in most of the derivatives A to C. For diboranes(4) of type A, unsymmetrical substitution with electron‐donating and ‐withdrawing groups at the boron centers is crucial to invoke fluorescence, albeit weak. Substitution at the boron atoms of 1,4‐diaza‐2,3‐diborinane species B leads to a modified skeletal structure. Finally, the grafting of 4‐(dimethylamino)phenyl groups to diboranes(4) of type C results in extraordinary Stokes shifts in nonpolar solvents.