Large and Tunable Wavelength Blue Shifts in Luminescent Piezochromism of Cu(I) Complexes via a Guest Encapsulation Strategy

For most piezochromic luminescent materials, mechanical stimuli usually result in a red shift and quenching of their luminescence. Materials that display blue-shifted and enhanced luminescence in response to mechanical stimuli are limited, and the related mechanism is difficult to investigate due to the unclear structural information. In this work, a series of Cu­(I) complexes that display blue-shifted and enhanced luminescence under pressure are designed via a guest encapsulation strategy. Detailed study reveals that, after grinding, the stacking mode of Cu­(I) complexes cracks and the encapsulated guests release rapidly, along with the decrease in the surrounding polarity of emitters and the corresponding luminescence change. Moreover, it is proven that, by adjusting the ratio of metal/halogen-to-ligand charge transfer, the pressure-induced luminescent blue shifts can be effectively modulated (from 40 to 90 nm). Also importantly, such piezochromic luminescence is recoverable. The rarely observed and large blue shift (90 nm) indicates the high availability for this guest encapsulation strategy as well.