Dihydroindeno[2,1-c]fluorene-based imide dyes: synthesis, structures, photophysical and electrochemical properties

A new kind of imide dyes based on dihydroindeno[2,1-c]fluorene have been developed. Consequently, a series of the organic dyes were conveniently and efficiently synthesized. The single crystal structure showed the dihydroindeno[2,1-c]fluorene core was almost planar, and the dye molecule could pack into herringbone-like structure in the solid state. It was found that the imide dyes all showed strong fluorescence emissions in tetrahydrofuran, and they also exhibited obvious red shifts with the increase of the π-conjugation system and the enhancement of the electronic-donating effect. Moreover, the electrochemical cyclic voltammograms of the imide dyes displayed irreversible redoxes in the film state. The electronic structures of aryl substituted imide dyes were also studied by the density functional theory (DFT), which gave a further explanation for their electrochemical behaviors.