Remarkable Piezochromism and Pressure-Induced Blue Emission Enhancement in Complex-Unit Copper Halides

Piezochromic luminescent materials (PLMs) exhibit potential applications in pressure sensing, anticounterfeiting, and optical memory. However, balancing a wide range of emission shifts with high pressure-sensitivity remains a challenge. Here, we achieved a considerable blue-shift piezochromism of 187 nm in zero-dimensional (0D) copper halide (TPA)2Cu4Br6 (TPA = Tetrapropylammonium), with a pressure coefficient over 80 nm/GPa below 10 kbar. Structural analysis confirmed that increased pressure deepened the high-energy self-trapped excitons (STEs) and disrupted the orderly arrangement of the [Cu4Br6]2– clusters. These two factors collectively diminished the interaction between STEs and depressed the formation of low-energy STEs, resulting in a significant blue shift in emission. Moreover, the decreased energy loss resulting from depressed phonon–phonon interaction led to a high photoluminescence quantum yield (PLQY) which remained over 70% during the blue-shift process and enabled the enhanced display performance as PLMs. This study demonstrated a highly sensitive PLM and revealed photophysical mechanism regarding the configuration and arrangement of complex clusters.