Structural engineering of fused imidazole luminogens through TPE functionalization toward reversible mechanochromic luminescence and preserved proton responsiveness.

Fused imidazole luminogens possess excellent photophysical properties, whereas introducing reversible mechanochromic luminescence without sacrificing their intrinsic proton-responsive characteristics remains a challenge. Herein, two TPE-functionalized fused imidazole luminogens, CzTPE-PI and CzTPE-PyI, were rationally designed by introducing twisted tetraphenylethene (TPE) units along the short molecular axis into phenanthroimidazole and pyrenoimidazole frameworks. The incorporation of the twisted TPE unit modulates molecular packing, endowing both luminogens with aggregation-induced emission enhancement characteristics and pronounced reversible mechanochromic luminescence. Upon mechanical grinding, the emission maxima of CzTPE-PI and CzTPE-PyI redshifted from 410 to 468 nm and from 426 to 474 nm, respectively. This reversible mechanochromic behavior enabled the construction of a solvent-free, rewritable anti-counterfeiting barcode for dynamic information encryption. Importantly, structural modification does not compromise the intrinsic proton-responsive characteristics of the fused imidazole framework. Upon exposure to trifluoroacetic acid (TFA), both luminogens exhibited remarkable fluorescence enhancement together with excellent sensing performance, affording detection limits of 19.4 and 19.2 nM. These findings show that TPE functionalization enables reversible mechanochromic luminescence while preserving the proton-responsive nature of fused imidazole luminogens, broadening their use in dynamic anti-counterfeiting and chemical sensing.