Clusteroluminescence in Maleimide: from Well-Known Phenomenon to Unknown Mechanism

Maleimide compounds have a long history related to colour reactions. It has been reported that maleimide yields bright colour when it reacts with basic reagents. Inspired by its colour formation, we investigated the maleimide polymer produced by an organic base 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The resultant polyimide contains exceptional fluorescence, which is virtually non-emissive in dilute solutions but exhibits strong pink emission (430nm and 580nm) in the concentrated solution and solid state. The intense colour comes from such a simple chemical structure, the unconventional fluorophore can be undoubtedly categorized into clusteroluminogens. By controlling the organic base amount, the intensity ratio of purple and orange-red emission can be controlled. The interaction between maleimide and base is rapid, and it can be achieved in the solid-solid interface or solid-gas interface. The aim herein is to highlight the recent observation and hold strong implications for further potential applications in anti-counterfeiting, gas sensors.