Solvatochromic Fluorescence Properties of Pyrazine–Boron Complex Bearing a β‑Iminoenolate Ligand

Pyrazine-based monoboron complexes bearing two fluorine atoms (BF₂ complex) or two phenyl groups (BPh₂ complex) on the boron atom were synthesized, and the fluorescence properties were investigated. The BPh₂ complexes exhibited red-shifted maximum absorption and maximum fluorescence wavelengths and lower molar absorption coefficients than the corresponding BF₂ complexes in <i>n</i>-hexane. The fluorescence quantum yields of the BPh₂ complexes were higher than or comparable to the corresponding BF₂ complexes owing to the relatively low nonradiative rate constants. Although the nonsubstituted and trifluoromethyl-substituted derivatives did not show solvatochromism, the dimethylamino-substituted BF₂ and BPh₂ complexes exhibited pronounced solvatochromism in the fluorescence spectra. Dual fluorescence was observed for the dimethylamino-substituted BF₂ complex in toluene, 1,4-dioxane, and chloroform, corresponding to locally excited (LE) and twisted intramolecular charge-transfer (TICT) states