Multi-color solid-state luminescence of difluoroboron β-diketonate complexes bearing carbazole with mechanofluorochromism and thermofluorochromism

• Difluoroboron β-diketonate complexes functionalized with carbazole were synthesized.
• The highest solid fluorescence quantum yields of difluoroboron complex reached 0.99.
• Reversible mechanofluorochromic behaviors were realized upon grinding and fuming.
• Ground powder of the complex with tert-butyl carbazole showed thermofluorochromism.

New difluoroboron β-diketonate complexes functionalized with tert-butyl carbazole and carbazole (TCBM and CBM) have been synthesized, and they give strong emission in solid states with the fluorescence quantum yields of 0.63 and 0.99, respectively. Reversible mechanofluorochromic behaviors of TCBM and CBM are realized upon the treatment of grinding/fuming with CH2Cl2. Interestingly, the emitting colors of the annealed samples gained from the ground powders of TCBM depend on the heating temperature, and change from orange to yellow, yellowish green, and green with increasing temperature. The X-ray diffraction patterns illustrate that the transformation processes from crystalline structure to partial destroyed crystalline structure, till to amorphous state lead to the multi-color solid-state luminescence during thermofluorochromism. We deduced that tert-butyl can lead to the incompact packing of luminophores, which is more sensitive to external stimuli, so that multi-color solid-state luminescence can be afforded during mechanofluorochromic and thermofluorochromic processes.

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