Dynamic Exciton Polarons Enabling Dual-Mode White-Light Emission with Tunable Color Temperatures in 2D Hybrid Lead...

White-light emission (WLE) with tunable chromaticity and correlated color temperature (CCT) is critical for lighting, display, and sensing applications. While recent two-dimensional (2D) lead halide perovskites have emerged as promising single-component WLE materials, their application is hindered by constrained and low CCT due to dominant localized exciton (LE) emission. Here, we report a dynamic exciton polaron mechanism in ⟨100⟩-oriented 2D lead bromides, (CH₂N₂)PbBr₄ (n = 5, 7, 9, 11), enabling intrinsic dual-mode WLE with widely tunable CCT. By combining ultrafast transient absorption spectroscopy and thermodynamic analyses, we reveal a double-well potential energy landscape driving the dynamic equilibrium between band-edge exciton (BE) and self-trapped LE states, and thus the formation of a dynamic exciton polaron. By elongating the ligand from n = 5 to 11, the self-trapping barrier decreases from 23.3 ± 1.3 to 10.1 ± 0.8 meV, and the trapping depth increases from 3.8 ± 0.4 to 14.7 ± 1.8 meV due to enhanced exciton-phonon coupling, which shifts the BE/LE emission ratio and tunes CCT from 21 000 K (bluish cold white) to 5100 K (reddish warm white). The dynamic exciton polaron with correlated BE and LE exhibits matched radiative lifetimes, ensuring stable dual-mode WLE without spectral distortion. Our work establishes that the dynamic exciton polaron, combined with ligand engineering, acts as a general principle for designing single-component multimode WLE materials with tailored chromatic properties, advancing their potential in efficient lighting and multifunctional optoelectronics.