Synthesis, crystal structure and reversible mechanofluorochromic properties of a novel phenothiazine derivative

Abstract

A dibenzoyl phenothiazine derivative containing two benzoyl groups has been synthesized via a Friedel-Crafts reaction. The new phenothiazine gave strong emission in solution and in solid state, and the solid fluorescence quantum yield was as high as 0.63. The single crystal structure of the phenothiazine revealed that the hydrogen bonds CH⋯C (2.864 Å), CH⋯C (2.850 Å), CH⋯O (2.652 Å) would lock the molecular conformation, and the twisted conformation of the molecule lead to poor solid molecular packing, yielding highly emissive behavior in its crystal. Moreover, reversible mechanofluorochromism of the phenothiazine was realized upon grinding/fuming or annealing. The emission color of the phenothiazine changed from green to yellow after grinding and could be restored via fuming with CH2Cl2 or heating. The XRD results show that the mechanofluorochromic nature is generated through crystalline-amorphous phase transformation under external pressure.