Polymorphism and mechanochromic luminescence of a highly solid-emissive quinoline-β-ketone boron difluoride dye

Abstract

A highly solid-emissive boron difluoride dye exhibiting polymorphism-dependent and mechanochromic luminescence has been synthesized. Three single-crystal X-ray structures of the polymorphic dye molecule, having different fluorescence emissions, are elucidated. Each polymorph displays different stacking orientations among their chromophore moieties and several different intermolecular interactions, which could be related to their different crystal emissions. The molecule displays piezochromic characteristics, with the fluorescence and quantum yield of both the solid powder and two kinds of crystals being reversibly adaptable to mechanical force and heating. The conversion between the monomer and π–π stacking-induced aggregate has been proposed as the mechanism behind the mechanochromism, according to X-ray diffraction measurements and differential scanning calorimetry analyses.