Piezofluorochromism in Aramid Dyads: Pressure-Triggered Luminescence Enhancement with Predictable Emission Shifts

Aggregation-induced emission has highlighted aramids as promising platforms for developing solid-state luminophores, broadening the conventional design landscape for these materials. Nonetheless, the simultaneous achievement of high efficiency and precisely tailored fluorescence in aramids remains a considerable challenge. Herein, high-pressure technique is employed to elucidate the critical structural determinants governing the emission intensity and shifts of aramids. Two representative aramid isomers, PP and OO, which exhibit distinct noncovalent conformation lock (NCL) effects, yield markedly different luminescence behaviors. For the PP crystal lacking NCL, pressure-induced molecular rigidity and planarity effectively restrict intramolecular phenyl-ring rotation. This constraint suppresses excited-state geometric distortion and enhances the population of excited electrons in higher vibrational states, ultimately giving rise to an unusual hypsochromic shift in luminescence. In contrast, the OO crystal, stabilized by NCL, exhibits a conventional bathochromic shift in emission, attributable to structural contraction and planarization upon compression. Collectively, these findings identify intrinsic intramolecular rotation as a decisive factor in governing the piezofluorochromic behavior of aramids, and further suggest conjugation modulation as a viable strategy for the precise tailoring of their piezofluorochromic properties.