Structure-property correlation of solid-emissive boron-fluorine derivatives

A series of solid-emissive BOPIM (boron 2-(2-pyridyl)imidazole complex) dyes, bearing electron-donating or -withdrawing substituents (methoxy, hydrogen, or nitro), are facilely synthesized. The compounds were characterized by H-1 NMR, C-13 NMR and MS. X-ray single crystal diffractions of BOPIM 1 and 2 indicate that nonplanar rigid structures were formed through intermolecular non-covalent interactions. Due to these non-covalent interactions, these dyes exhibit intense fluorescence in solution and also in solid state. According to H-1 NMR analysis, electronic effect of the substitutes plays an important role in contribution to these BOPIMs' electronic states. The photophysical measurements reveal that electron-donating groups (methoxy) lead to significant bathochromism of the absorption and emission. In contrast, electron-withdrawing moieties (nitro) play the reverse role. However, BOPIM 3 bearing nitro groups emits long wavelength fluorescence in solid state, probably due to the formation of intermolecular hydrogen bond. This work elucidates the spectroscopic structure-property relationship of solid-emissive BOPIMs, which would be valuable for design of solid-emissive dyes. (C) 2012 Elsevier B. V. All rights reserved.