Controlled Synthesis of Cyclopenta-Fused B ₂ N ₂ -Pyrene and Diazaborepin: Structures and Photophysical Properties

Cyclopenta-fused B 2 N 2 -pyrene ( B 2 N 2 CP ) and diazaborepin ( NBNM ) have been accomplished from a common bi-indole precursor in three steps. Borylative cyclization of bi-indoles with 2.0 equiv of BCl 3 afforded NBNM as the major product, whereas increasing the amount of BCl 3 to 3.0 equiv delivered B 2 N 2 CP as the major product. Both B 2 N 2 CP and NBNM are highly emissive in solution. B 2 N 2 CP emits in the deep-blue region, while NBNM emits in the blue-to-green region. Moreover, we found that fluoride anion addition to the solution of B 2 N 2 CP and NBNM led to a great change in their absorption and emission spectra.