Synthesis and Photophysical Properties of Aryl-Substituted 2-Borylbenzaldimines and Their Extended π-Conjugated Congeners

Novel N-aryl-substituted 2-borylbenzaldimines 6 and related systems with extended π-framework 7 based on two borylbenzaldimine units linked by a spacer
moiety were synthesized by condensation reactions of 2-(dimesitylboryl)­benzaldehyde 3 with various amines 4 and diamines 5. All compounds were completely characterized including X-ray diffraction,
especially in view of Lewis acid–base B–O and B–N
interactions. The electronic as well as the photophysical properties
of bisimines 7 were determined using cyclic voltammetry,
UV/vis, and fluorescence spectroscopy and quantum chemistry. These
compounds feature large Stokes shifts and reversible reduction waves.
Interestingly, UV irradiation experiments unfold enhanced photostability
for compounds 7 with an extended π-skeleton. By
use of 1,8-diaminonaphthalene we observed the formation of a hitherto
unknown BN-heterocyclic compound 9 fused with a perimidine
skeleton. Structural and energetic aspects were evaluated by high
level quantum chemical methods (DFT and SCS-MP2-calculations).