A novel central seven-membered BOPYOs: Synthesis, optical properities and optimization of BF₂ removal

Many efforts have been made to enrich the variety of BF₂ complexes because of their excellent optical properties. However, the investigation on seven-membered ring N, O-chelated BF₂ complexes is rare due to their instability with the removal of BF₂ unit. Herein, a novel seven-membered ring N, O-chelated BF₂ complexes (BOPYOs) with dual-state emission has been synthesized via a facile method. The results of optical properties showed that the fluorescence quantum yield of BOPYO-2 with donor group on 1 and 2-position of 1-indanone unit is much higher than that of BOPYO-1, 3-5 in toluene. The emission spectra of BOPYO-6 or 7 have redshift phenomenon compared with BOPYO-1-5 with weak fluorescence intensity due to their highly distorted structure or intramolecular charge transfer (ICT) effect. BOPYOs show relatively moderate solid emission from orange to deep red color with 596 nm to 686 nm. On the contrary, fluorescence quantum yield of BOPYO-2 in solid is the lowest. The optical properties in solution and solid states are further supported by the single-crystal structure and DFT calculation. Furthermore, the investigation on optimization of BF₂ removal shows that the corresponding precursors of BOPYOs could be obtained in protic solvents without adding other catalysts.