Fluorene-containing binuclear gold(I) complexes: High-contrast mechanochromic fluorescence quenching and information encryption application

A series of fluorene-based binuclear gold(I) complexes I–VI have been successfully synthesized. Their structures were characterized by nuclear magnetic resonance, high-resolution mass spectrometry, and single crystal X-ray diffraction techniques. The fluorescence switching characteristics of complexes I–VI in the solid state were studied by photoluminescence spectroscopy. Luminogens I–VI showed different solid-state fluorescence involving blue-green, yellow-green and yellow colors before mechanical stimulation, which suggests that the solid fluorescent properties of I–VI can be effectively manipulated by positional isomerism and increasing conjugation strategies. Interestingly, their solid fluorescence intensities of all luminogens weakened significantly upon grinding. Impressively, luminogen IV barely displayed macroscopic fluorescence after grinding, indicative of its remarkable high-contrast mechanochromic fluorescence quenching feature. The unique mechanofluorochromic phenomena of I–VI were fully elucidated by analyzing X-ray diffraction patterns changes of I–VI before and after grinding and crystal packing structure of III. Furthermore, an effective dual information encryption system was constructed based on complex IV.