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

Abstract

Herein, two new quadrupolar acceptor-p-donor-pacceptor (A-p-D-p-A) chromophores have been prepared featuring as trongly electron-donating diborene core and strongly electron-accepting dimesitylboryl (BMes 2 )a nd bis(2,4,6-tris(trifluoromethyl)phenyl)boryl (B F Mes 2 )e nd groups.A nalysis of the compounds by NMR spectroscopy, X-ray crystallography,c yclic voltammetry,a nd UV/Vis-NIR absorption and emission spectroscopyi ndicated that the compounds have extended conjugated p-systems spanning their B 4 C 8 cores.T he combination of exceptionally potent pdonor (diborene) and p-acceptor (diarylboryl) groups,b oth 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 and very high extinction coefficients of ca. 120 000 m À1 cm À1 .B oth molecules also displayw eak near-IR fluorescence with small Stokes shifts.

Insights into the Optical Properties of Triarylboranes with Strongly Electron‐Accepting Bis(fluoromesityl)boryl Groups: when Theory Meets Experiment

“…Alternative bulky groups with higher electron affinities should enhance acceptor strength while maintaining or even enhancing the desired chemical stability of the systems. [6,12,28,[36][37][38][57][58][59][60][61][62][63][64][65][66][67] Exploiting this favorable property, some of us recently reported a series of air-stable bis (fluoromesityl)boryl ((FMes) 2 B) derivatives, namely compounds 1-3 (Scheme 1) with different electron-donating groups for comparison, i. e., phenyl, 4-tert-butylphenyl and 4-N,N-diphenylaminophenyl, respectively, attached to the electron acceptor group (FMes) 2 B through BÀ C bonds. [12] Comparison of these (FMes) 2 B-containing donor-acceptor compounds with compound 4, which contains a (Mes) 2 B group (Scheme 1), confirms that (FMes) 2 B is a much stronger acceptor, leading to: (i) a larger quinoidal distortion in the ground state structure; (ii) significantly red-shifted emission in solution and in the solid state; (iii) stronger emission solvatochromism; and (iv) significantly lower reduction potentials.…”

Oxoborane Formation Turns on Formazanate‐Based Photoluminescence

“…[14] While heterocycles containing BC [15] or BN [16] bonds with some p character are common, there appear to be no reports of photoluminescence induced by the formation of terminal double or triple bonds to boron.I nt his work, we demonstrate that the formation of the oxoborane (B=O) group transforms normally non-emissiveb oron triarylformazanate complexes into ap hotoluminescent compound. Electron-rich diborenes have also been paired with p-accepting diarylboryls to produce molecules with near-IR photoluminescence.…”

“…Electron-rich diborenes have also been paired with p-accepting diarylboryls to produce molecules with near-IR photoluminescence. [14] While heterocycles containing BC [15] or BN [16] bonds with some p character are common, there appear to be no reports of photoluminescence induced by the formation of terminal double or triple bonds to boron.I nt his work, we demonstrate that the formation of the oxoborane (B=O) group transforms normally non-emissiveb oron triarylformazanate complexes into ap hotoluminescent compound. More generally,w es uggest that combining boron multiple bonds and pro-photoluminescent ligands may be an effective general approach for the production of photoluminescent materials.…”

Triarylborane‐Based Helical Donor–Acceptor Compounds: Synthesis, Photophysical, and Electronic Properties

“…[13] In these compounds the boron center has av acantp z -orbital,w hich acts as as trong p-electron acceptor in conjugated organic p-systems. [14] However,t he boron atom can still be easily attacked by air,w ater,a nd other nucleophiles. Bulky substitutions are therefore used to protect the boron center.…”