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

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.