Tunable near-infrared piezochromic luminescence by effective substituent modification of D-A structures

Piezochromic luminescent (PCL) materials have attracted extensive research interest due to their potential applications in mechanosensors, ink-free printing, optical data storage, optoelectronic devices, etc. However, there have been few reports on the near-infrared (NIR) piezochromic luminescence of pi-conjugated organic materials under external hydrostatic pressure. Herein, we report the design and preparation of five pressure-sensitive AIEgens: TPAM, BTPAM, FTPAM, MTPAM and MOTPAM. These materials exhibit piezochromic luminescence behaviors, whereby their emission colors exhibit significant blue-shifts upon gentle manual grinding due to the phase transition from the crystalline to the amorphous state. With an increase in applied hydrostatic pressure, significant emission red-shifts (up to >200 nm) toward the NIR region were observed with the modification of substituents, attributed to the enhanced intermolecular pi-pi interactions. The unsubstituted TPAM did not exhibit any red-shifted emission due to the synergistic effect between enhanced intermolecular interactions and molecular configuration deformation during the compression process.