1‑Azaazulene: A Ligand Moiety for Boron Difluoride (BF2) Complexes To Achieve Long-Wavelength Absorption

1-Azaazulene was adopted as a new ligand moiety for boron difluoride (BF2) complexes, resulting in large red shifts of the absorption bands up to 103 nm compared to their isomeric quinoline-based complexes. Such change was attributed to the nonalternant nature of 1-azaazulene, as the complexes maintained the intrinsic 10π-peripheral electronic structure. 1a exhibited the most red-shifted absorption among reported BF2 complexes containing a phenolic backbone, and the absorption edge of 1b reached the red region.