Near-Infrared Quadrupolar Chromophores Combining Three-Coordinate Boron-Based Superdonor and Superacceptor Units

Herein, two new quadrupolar acceptor--donor--acceptor (A--D--A) chromophores have been prepared featuring a strongly electron-donating diborene core and strongly electron-accepting dimesitylboryl (BMes(2)) and bis(2,4,6-tris(trifluoromethyl)phenyl)boryl (B(F)Mes(2)) end groups. Analysis of the compounds by NMR spectroscopy, X-ray crystallography, cyclic voltammetry, and UV/Vis-NIR absorption and emission spectroscopy indicated that the compounds have extended conjugated -systems spanning their B4C8 cores. The combination of exceptionally potent -donor (diborene) and -acceptor (diarylboryl) groups, both based on trigonal boron, leads to very small HOMO-LUMO gaps, resulting in strong absorption in the near-IR region with maxima in THF at 840 and 1092nm and very high extinction coefficients of ca. 120000m(-1)cm(-1). Both molecules also display weak near-IR fluorescence with small Stokes shifts.