Highly sensitive X-ray responsive molecular switches

X-ray-triggered molecular switching promises remote control behind physical barriers, yet existing radioswitches typically require multi-gray doses to reach a photostationary state. Here we route X-ray energy through triplet excitons to enable low-dose switching. An efficient scintillator acts as a triplet sensitizer, transferring energy to a photoswitch with lower triplet energy via triplet-triplet energy transfer (TTET). Flexible films combining a Cu₂I₂(POP)₂ scintillator with hydrazone switch 1-I reach a photostationary state at ~0.18 Gy and show a detection limit near 0.01 mGy, about two orders of magnitude lower than previous systems. HPLC quantification, radical-scavenger tests, and time-resolved spectroscopy support a TTET-dominated mechanism and establish a design rule based on triplet-level matching. Isomerization quenches fluorescence, enabling optical readout for high-resolution radiography (3251 dpi) with pattern retention for at least two months. In this work, we show that penetrating X-rays enable practical control of molecular functions in previously inaccessible complex environments.