Pressure-Induced\nUltrawidely Tunable and Ultrapure\nPhotoluminescence in 2D Perovskites via Fluorination of Organic Cations

Alternating organic and inorganic\nlayers of two-dimensional\n(2D)\nperovskites provide a feasible route for extending their emission\nrange through external pressure. However, lattice distortion of inorganic\nlayers under pressure significantly impedes narrow-band emission.\nHerein, we report a simple approach through fluorination of organic\ncations in 2D (PEA)<sub>2</sub>PbI<sub>4</sub> to improve structural\nrigidity and sustain tunable narrow-band emission. Most importantly,\n(4-FPEA)<sub>2</sub>PbI<sub>4</sub> exhibits ultrapure photoluminescence\nemission with a spectral width of 14–21 nm and an ultrawide\ntunability range from 520 to 695 nm with excellent linearity and reversibility\nupon compression to 7 GPa. Our findings demonstrate that fluorine\nsubstitution on the para position of the phenyl group in (4-FPEA)<sub>2</sub>PbI<sub>4</sub> can promote the parallel stacking alignment\nof PEA molecules and enhance the interactions between spacer cations,\nwhich maximally release the compression to the inorganic framework\nunder compression. This work could open new pathways for developing\n2D perovskites with ultrawide wavelength tuning and high color purity\nfor display applications.