Zipper‐Like Dynamic Switching of Coordination Bonds Gives a Polar Bimetallic Halide Toward Self‐Driven X‐Ray Detection

Polar molecular crystals hold a promise for controlling bulk physical properties originated in their unique switchable polarity via structural transformation. However, the mechanisms for switching polarization are mainly limited to displacive and disorder-order phase transitions, which rarely involve the reconstruction of chemical bonds. Here, we have switched and tuned electric polarization in a bimetallic halide, (Neopentylammonium)₄AgBiBr₈ (1), as verified by light-excited pyroelectric effect. Most notably, its Ag-Br coordination bonds show a zipper-like dynamic switching behavior from the 'locked' to 'unlocked' state, namely, reconstruction of chemical bonds. Coupling with the dynamic ordering of organic cations, this bond-switching transition makes a contribution to switchable polarization of 1. As expected, its polarity creates pyroelectric effect for self-driven X-ray detection with high sensitivity (3.8×10³ μC Gy^-1 cm^-2) and low limit of detection (4.8 nGy s^-1). This work on the bond-switching mechanism provides an avenue to design polar molecular candidate for smart optoelectronic devices.