Defect-sensitive crystals based on diaminomaleonitrile-functionalized Schiff base with aggregation-enhanced emission

In this work, we report the synthesis and photophysical studies of a new luminogen, A3MN, a diaminomaleonitrile-functionalized Schiff base. A3MN is aggregation-enhanced emission (AEE)-active: the emission of A3MN is enhanced with the aggregate formation. A3MN also possesses twisted intramolecular charge transfer (TICT) properties, showing noticeable solvatofluorochromism. Interestingly, the crystals of A3MN are nonemissive; the defect areas of the crystal, however, are highly emissive, as confirmed by spectroscopic methods and confocal microscopy. By taking advantage of this defect sensitive feature, a "turn-on" type of mechanofluorochromic material is developed, the emission of which is significantly enhanced under pressure or shear force. The detection limit reaches 0.1 Newton owing to its "turn-on" nature. Such defect-induced emission also renders A3MN sensitive to various kinds of mechanical actions, including hitting, friction, sculpture, and ultrasonic vibration.