Electron-Transfer Photochromism for Enhanced Near-Infrared Photoelectric Response in a Semiconductive Coordination Polymer

Near-infrared (NIR) photoelectric materials have garnered increasing attention due to their broad potential in biomedical imaging, night vision, and health monitoring. Coordination polymers (CPs), with tunable structures and functionalities, have emerged as promising candidates in this area. However, CPs exhibiting efficient NIR photoelectric response remain limited. Herein, we report a photochromic coordination polymer [K(HAlaNDI)]_<i>n</i> (<b>1</b>), constructed from an electron-deficient naphthalenediimide (NDI) derivative. Upon Xe lamp irradiation, compound <b>1</b> exhibits distinct color change from light brown to deep brown, accompanied by the emergence of broad absorption bands and a strong EPR signal. After photoirradiation, the NIR photothermal conversion performance of <b>1</b> was significantly enhanced, with the surface temperature rise (Δ<i>T</i>) increasing by approximately 80%. Concurrently, the electrical conductivity of <b>1</b> increased by nearly an order of magnitude, from 7.24 × 10^-9 to 6.19 × 10^-8 S/cm at 30 °C. These enhancements could be primarily ascribed to the generation of stable charge-separated states (NDI^·-). As a result, the colored form of <b>1</b> exhibits significantly enhanced NIR photoelectric response, with the on/off ratio increasing by over 50% across a wide range of power densities, highlighting electron-transfer-type photochromism as an effective strategy for improving NIR photoelectric performance.