1‑Azaazulene: A Ligand Moiety for Boron Difluoride\n(BF<sub>2</sub>) Complexes To Achieve Long-Wavelength Absorption

1-Azaazulene was adopted as a new\nligand moiety for boron difluoride\n(BF<sub>2</sub>) complexes, resulting in large red shifts of the absorption\nbands up to 103 nm compared to their isomeric quinoline-based complexes.\nSuch change was attributed to the nonalternant nature of 1-azaazulene,\nas the complexes maintained the intrinsic 10π-peripheral electronic\nstructure. <b>1a</b> exhibited the most red-shifted absorption\namong reported BF<sub>2</sub> complexes containing a phenolic backbone,\nand the absorption edge of <b>1b</b> reached the red region.