Flexible Viologen‐Based Porous Framework Showing X‐ray Induced Photochromism with Single‐Crystal‐to‐Single‐Crystal Transformation

Abstract A viologen‐based Borromean entangled porous framework was found to be sensitive to both Cu Kα and Mo Kα X‐ray sources, showing rapid photochromic response and recovery within one minute. The X‐ray‐induced photochromic process is accompanied by a reversible single‐crystal‐to‐single‐crystal (SC‐SC) structural transformation, an unprecedented phenomenon for X‐ray sensitive materials. The complex can be further processed into portable thin films for detecting the dose of the X‐ray exposure. Moreover, the photochromism can occur over a broad temperature range of 100–333 K, both in the form of single crystals and thin films, making it a potential candidate for practical indoor and outdoor applications.