Radiochromic Hydrogen‐Bonded Organic Frameworks for X‐ray Detection

Porous materials have been investigated as efficient photochromic platforms for detecting hazardous radiation, while the utilization of hydrogen bonded organic frameworks (HOFs) in this field has remained intact. Herein, two HOFs were synthesized through self‐assembly of tetratopic viologen ligand and formic acid (PFC‐25, PFC‐26), as a new class of “all‐organic” radiochromic smart material, opening a gate for HOFs in this field. PFC‐26 is active upon both X‐ray and UV irradiation, while PFC‐25 is only active upon X‐ray irradiation. The same building block yet different radiochromic behaviors of PFC‐25 and PFC‐26 allow us to gain a deep mechanistic understanding of the factors that control the detection specificity. Theoretical and experimental studies reveal that the degree of π‐conjugation of viologen ligand is highly related to the threshold energy of triggering a charge transfer, therefore being a vital factor for the particularity of radiochromic materials. Thanks to its convenient processibility, nanoparticle size, and UV silence, PFC‐25 can be further fabricated into a portable naked‐eye sensor for X‐ray detection, which shows obvious color change with the merits of high transmittance contrast, good sensitivity (reproducible dose threshold of 3.5 Gy), and excellent stability. The work exhibits the promising practical potentials of HOF materials in photochromic technology. Hydrogen bonded organic frameworks (HOFs) were explored as radiochromic materials responsive to X‐ray irradiation, opening a new avenue for their application. The HOFs reported here have the same building block yet different radiochromic behaviors: one is sensitive to both X‐ray and UV light, while the other one is specifically responsive to X‐ray light. These phenomena provide a precious chance to understand the vital factors that account for the detection specificity of radiochromic materials.