4,7-Bis[3-(dimesitylboryl)thien-2-yl]benzothiadiazole: Solvato-, Thermo-, and Mechanochromism Based on the Reversible Formation of an Intramolecular B-N Bond.

4,7-Bis-[3-(dimesitylboryl)thien-2-yl]benzothiadiazole (1) and monoborylated derivative 2 were synthesized and their chromic behavior was investigated. Photophysical measurements, single-crystal XRD analysis, and theoretical calculations revealed that an intramolecular B-N coordination bond formed reversibly. The equilibrium of this reversible bond formation depends on the solid-state structure, solvent, temperature, and mechanical forces, and leads to significant changes in the electronic structure and chromic behavior of these molecules. The responsiveness toward external stimuli, resulting in the reversible formation of open and closed forms of this system, is achieved through weak intramolecular B-N coordination bonds induced by the steric bulk of the mesityl groups on the boron centers.

In†Situ Solid-State Generation of (BN)2 -Pyrenes and Electroluminescent Devices.

New BN-heterocyclic compounds have been found to undergo double arene photoelimination, forming rare yellow fluorescent BN-pyrenes that contain two BN units. Most significant is the discovery that the double arene elimination can also be driven by excitons generated electrically within electroluminescent (EL) devices, enabling the in situ solid-state conversion of BN-heterocycles to BN-pyrenes and the use of BN-pyrenes as emitters for EL devices. The in situ exciton-driven elimination (EDE) phenomenon has also been observed for other BN-heterocycles.

NIR-Absorbing Dye Based on BF2-Bridged Azafulvene Dimer as a Strong Electron-Accepting Unit.

BF2-bridged azafulvene dimers designed to be strong electron-accepting units were selectively synthesized using a bulky base. Single-crystal X-ray diffraction analysis revealed that the high electron-accepting ability of this structure stems from the contribution of the π-conjugation mode of the azafulvene dimer upon formation of B-N coordination bonds. As a result of the low-lying LUMO energy of this electron-accepting unit, the corresponding D-A-D dye exhibits an intense NIR absorption band at 922 nm, which tails up to 1150 nm, while significant absorption bands in the visible region are absent. As a NIR dye this molecule exhibits moreover exceptional photostability and resistance to oxidation by atmospheric oxygen, even in dilute solution.