Pressure‐Driven Photoluminescence Spectral Narrowing in X‐Aggregates Dye via Self‐Absorption Effect

Abstract Piezochromic materials typically exhibit spectral broadening and photoluminescence (PL) quenching, largely due to the formation of multiple emissive species and non‐radiative states. Achieving pressure‐induced spectral narrowing in organic systems, however, remains elusive. Herein, we report the first observation of pressure‐driven PL spectral narrowing in ZPH crystals, a multi‐resonant emitter featuring B/N‐skeletons and characterized by an X‐aggregate packing motif and strong absorption‐PL spectral overlap. Under hydrostatic pressure, the absorption‐PL spectral overlap markedly increases. This enhanced spectral overlap intensifies the self‐absorption effect, thereby diminishing the intensity of the main PL peak. Concurrently, below 8.93 GPa, the exciton coupling of X‐aggregates is slightly weakened, resulting in an enhancement of the PL shoulder peak. The opposing intensity changes of these dual peaks, attributable to the combined effects of intensified self‐absorption and weakened X‐aggregate exciton coupling, collectively lead to the observed pressure‐induced spectral narrowing. This work establishes a counterintuitive strategy by leveraging self‐absorption for spectral control, thereby advancing our understanding of how the self‐absorption influences photophysical properties.