Near‐infrared quadrupolar chromophores combining three‐coordinate boron‐based superdonor and ‐acceptor units

In this work, two new quadrupolar A‐π‐D‐π‐A chromophores have been prepared featuring a strongly electron‐donating diborene core and strongly electron‐accepting dimesitylboryl (BMes2) and bis(2,4,6‐tris(trifluoromethyl)phenyl)boryl (BFMes2) 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 possess extended conjugated π‐systems spanning their B4C8 cores. The combination of exceptionally potent π‐donor (diborene) and π‐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 1092 nm, respectively, and very high extinction coefficients of ca. 120,000 M‐1cm‐1. Both molecules also display weak near‐IR fluorescence with small Stokes shifts.

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