Lattice Distortion Promoting Wavelength‐Tunable Emissions in Cu(I)‐Based Halides for Thermography and Anti‐Counterfeiting

Low‐dimensional hybrid metal halides as a chemically tunable platform achieve multi‐functional optical applications with versatile luminescence mechanisms. Herein, we design and prepare Cu(I)‐based hybrid halide (DMAP)Cu3I4 (DMAP = 4‐Dimethylaminopyridine), with ambient temperature‐induced photoluminescence evolution from red to near‐infrared emissions. The in‐situ variable‐temperature crystallographic study reveals lattice distortion with more disordered [Cu3nI4n]n‐ units appear at high temperature, further indicating that the observed wavelength‐tunable emission is attributed to transitions from Cu cluster center to halogen‐to‐metal charge transfer. Thus, (DMAP)Cu3I4 shows a compelling thermometric precision (high sensitivities of 0.0001‐0.6 K‐1) at a wide temperature range of 80–300 K. In particular, the remote thermography is established with a high spatial resolution of ~20 lp mm‐1 by processable thin films. These findings enhance the potential for molecular‐level illumination in Cu(I)‐based halides and contribute to the exploration of their optoelectronic properties.