Red to near-infrared piezochromism from AIE-active luminophores: isolated dimers facilitating a wide-range redshift

Near-infrared piezochromic materials (PCMs), presenting a fluorescence response with a clear colour difference (large spectral shift) and strong penetrability, have practical applications as pressure sensors. Nevertheless, examples achieving a distinct redshift are very rare in the deep-red to near-infrared region. Herein, an asymmetric luminophore, TDCH, was developed by end-capping a benzothiadiazole core with nonconjugated cholesteryl and twisty triphenylamine (TPA) units, which exhibits aggregation-enhanced emission behaviour. Impressively, TDCH molecules adopt isolated dimeric packing and emit deep-red fluorescence at 675 nm with a high emission efficiency (89.7 and 44.3% for doped film and crystalline powder, respectively). These neighbouring dimers, fully separated by TPA units, are related to the nonconjugated cholesteryl groups. At high pressure, pi-pi interactions between adjacent dimers are weakened by nonconjugated cholesteryls. As a result, this luminophore demonstrates the deep-red to near-infrared piezochromic properties with a wide-range redshift (157 nm) and high sensitivity (22.1 nm GPa(-1)).