Mechanochromic Luminescence of Fluorenyl-Substituted Ethylenes

It has been reported several times that some organic luminogens with aggregation-induced emission (AIE) characteristics exhibit the abnormal phenomenon of crystallization-induced blueshift fluorescence, which makes them suitable for utilization as luminescence color-switching materials. Because of the attractive application potential and the numerous underlying structure-property relationships in such materials, we investigated a series of fluorenyl-containing tetrasubstituted ethylenes for their novel optical properties and structural features. The dyes show morphology-dependent luminescence. Their emission color can be switched between green and blue by means of mechanical grinding and solvent fuming. The transformation between crystalline and amorphous accounts for the luminescence changing. Through single-crystal and X-ray diffraction (XRD) analysis, the twisted molecular geometries and loose packing motifs in the crystalline samples are believed to be the intrinsic origin of the external-stimuli-induced structural transformation.