Near-infrared piezochromism of AIE-active luminophore in hybridized local and charge-transfer excited statethe effect of shortened donor-acceptor distance

A close-bonded D-A-D' luminophore BOTPA was designed via direct coupling of secondary arylamine derivatives (D, D') with benzothiadiazole cyanostilbene group (A). Both near-infrared (NIR) aggregation-induced emission (AIE) and hybridized local and charge-transfer (HLCT) effects, which endow it with highly efficient NIR piezochromic performance, are observed owing to its especially short D-A distance and twisted conformation. The luminophore shows bright fluorescence at 740 nm with an absolute photoluminescence quantum yield (PLQY) as large as 13.2%. Remarkable piezochromism with high sensitivity (11.0 nm.Gpa(-1)) completely in the NIR region (700-840 nm) could be observed from BOTPA crystals, which is rarely found in piezochromic materials (PCMs). The effects of the shortened D-A distance towards the highly efficient NIR piezochromism are confirmed via single-crystal analysis, in-situ FTIR and theoretical calculations. This work provides a new strategy for the development of high-efficiency NIR PCMs which possess strong penetrating capacity.