BODIPY dye possessing solid-state red fluorescence and green metallic luster properties in both crystalline and amorphous states

Abstract

Carbazole-BODIPY dyes YHO-2 and YHO-3, which have diphenylamino-carbazole moiety as an electron-donating group at the 8-position on the BODIPY core, and heptanoic acid for YHO-2 and ethyl heptanoate for YHO-3 on the carbazole ring, were designed and synthesized and their photophysical properties in solution and in the solid state were investigated. Absorption and fluorescence properties of YHO-2 and YHO-3 are similar in solution, and both the dyes exhibited moderate fluorescence quantum yields. However, as-recrystallized dye YHO-3 exhibits solid-state red fluorescence but as-recrystallized dye YHO-2 exhibits feeble solid-state fluorescence properties. Interestingly, the dye YHO-3 possesses green metallic luster properties in both crystalline and amorphous states. Moreover, it was found that by grinding the as-recrystallized dye YHO-3, the disappearance of the metallic luster property and the blue-shift of the fluorescence maximum were observed in the ground solid. On the basis of X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC), the solid-state photophysical properties of the carbazole-BODIPY dyes are discussed.