Boron difluoride functionalized (tetrahydroimidazo[1,5-a]pyridin-3-yl)phenols: Highly fluorescent blue emissive materials

Some (tetrahydroimidazo[1,5-a]pyridin-3-yl)phenols were reacted with boron trifluoride diethyl etherate and the resulting BF2-functionalized compounds were fully characterized both in solution using 1H, 13C, 11B, 19F NMR spectroscopy and in the solid state (infrared, fluorescence, X-ray). When excited with UV light these boron difluoride derivatives show in dichloromethane solution an intense fluorescence emission in the UV region, with λmax of emission varying from 357 to 390 nm. Good absolute quantum yields are recorded for most of the compounds. In the solid state, they are characterized by a strong blue emission (388–435 nm), with high absolute quantum yields (up to 0.68) and x,y color coordinates (CIE 1931) close to those expected for standard blue. Time-Dependent Density Functional Theory (TD-DFT) calculations were used to define the nature of the electronic transitions and excited states involved in the fluorescence process.