Selective Photochromic Response to Low-Dose X-ray Radiation Detection in One-Dimensional Cadmium-Viologen Complexes

Photochromic viologen-based materials have emerged as one of the most promising candidates for the development of X-ray light detection applications, including medical diagnosis and treatment, environmental radiation inspection, and industrial crack detection. However, the design and construction of low-dose X-ray-sensitive complexes remains an immense challenge, especially for the in-depth dissection of their response mechanisms. Herein, by using N,N'-4,4'-bipyridiniodipropionate (CV) as functional sensitive structural units and cadmium as heavy atoms, two cadmium-viologen complexes with one-dimensional chained structures, namely, [Cd₂Cl₄(CV)(H₂O)₂]_n (1) and [CdBr₂(CV)]_n (2), have been constructed, which exhibit a remarkable and selective photochromic response to low-dose X-ray radiation detection. Compound 1 is visually sensitive to both X-ray and UV light due to the more accessible photoinduced electron transfer (ET) pathways, while compound 2 only shows a slight color-changing process in response to UV light, in conformity with UV-vis absorbance analyses and kinetic studies. Surprisingly, compound 2 has longer ET pathways than 1, but not in response to high-energy X-ray light, seeming to contradict the previous phenomena. On further analysis, the key point in achieving X-ray-sensitive behavior should be a good balance among the electron donor-acceptor distance, intermolecular interaction, and X-ray absorbing capacity, as verified by density functional theory (DFT) and X-ray absorption strength calculations, X-ray photoelectron spectra, electron paramagnetic resonance measurements, and independent gradient model analysis. In particular, compound 1 is unprecedentedly sensitive to soft X-ray radiation, accompanied by an X-ray detection limit of as low as 2.91 Gy. These findings push forward the further development of low-dose X-ray sensing materials.

A photochromic and scintillation Eu-MOF with visual X-ray detection in bright and dark environments

The detection of X-rays has always been a frontier of scientific research. An Eu-MOF with both X-ray-induced photochromic and scintillation properties has been synthesized through the combination of a photochromism-active viologen ligand and rare earth Eu element with high-efficiency absorption of X-rays. In a bright environment, Eu-MOF exhibits different color changes under high-energy X-rays and low-energy X-rays, which can effectively distinguish X-rays. Eu-MOF can also be used for X-ray detection by scintillation properties in dark environments. This work provides a new perspective on the design of multifunctional materials that can perform simple X-ray detection in different environments.

Theoretical Limit of the Color-Change Sensitivity of a Composite Resin Dosimeter Film Based on Spiropyran/BaFCl : Eu2+/Polystyrene

The theoretical limit of the color-change sensitivity of a composite resin dosimeter film based on 6-nitro BIPS/BaFCl : Eu2+/polystyrene under X-ray exposure has been estimated. Each photophysical and photochemical process occurring inside the composite resin dosimeter was quantitatively determined, and the obtained values were used to estimate the theoretical limit of the color-change sensitivity for the composite resin dosimeter. The values obtained were 70.6 % for the X-ray absorption efficiency, 13 % for the fluorescence quantum yield, 73.5 % for the UV absorption efficiency and 37.6 % for the photochemical quantum yield. Assuming that the figure-of-merit is their product, its value is estimated to be 2.5 %, which contributes to the chromaticity difference and leads to a color-change sensitivity of 100 mGy. The figure-of-merit of a structurally optimized composite dosimeter was estimated to be 1.9 times that of the dosimeter without structural optimization, which showed a sensitivity of 100 mGy. We predicted that the structurally optimized composite resin dosimeter film, which eliminates optical losses due to the structure, will be able to detect X-ray exposure doses on the order of approximately 28 mGy.

Photosynergetic amplification of radiation input: from efficient UV induced cycloreversion to sensitive X-ray detection

Five photochromic terarylenes which show reversible photocyclisation and cycloreversion with relatively high quantum yields are presented. Some of these have been observed to undergo a highly efficient cycloreversion cascade process from their coloured, closed forms to their uncoloured open forms that leads to cycloreversion quantum yields significantly larger than unity. This cascade effect can been induced with both chemical and X-ray initiation; the limit of detection from X-ray initiation has been tested and is comparable to existing systems with detection observed at values as low as 0.3 mGy.

New photochromic terarylene displays extremely high photosensitivity with quantum yield as high as 3300% and radio-sensitivity to X-ray dose as weak as 0.3 mGy.

Leuco-Based Composite Resin Dosimeter Film

A polystyrene (PS)-based composite resin dosimeter (CRD) film comprising 2-(phenylamino)-6-(dipentylamino)-3-methylspiro[9H-xanthene-9,3'-phthalide] (Black305) fluoran leuco dye, cerium-doped yttrium aluminum perovskite YAlO₃:Ce (YAP:Ce) scintillator, and 2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine (MBTT) photoacid generator was developed for the visualization of X-ray exposure doses in the range of 18-170 Gy. The color of the CRD film changed from yellow to black within this range based on the X-ray exposure dose. A CRD film based on Black305/YAP:Ce/MBTT/PS could be used to produce a dosimeter with various color change sensitivities by controlling the thermodynamic parameters of the constituent materials. A CRD film is a promising tool for measuring the X-ray exposure dose and can be used as an alternative to the existing radiochromic dosimeters.

An inorganic–organic hybrid photochromic material with fast response to hard and soft X-rays at room temperature

The first X-ray-induced photochromic material, with the coloration time being within 5 min when exposed to Mo-K_α and Al-K_α X-rays, was designed and synthesized.

Energy-dependent photochromism at room temperature for visually detecting and distinguishing X-rays

A radiochromic material with energy-dependent X-ray-induced photochromism was obtained by incorporating a radiosensitive ligand into an electron-transfer photochromic metalloviologen system.

A spiropyran-based X-ray sensitive fiber

This study attempted to visualize reversible X-ray radiation by using a poly-(l-lactic acid) (PLLA) composite fiber with an average diameter of 150 μm. The fiber contains photostimulable phosphor (PSP) BaFCl:Eu(2+) particles that are subsequently dyed with the photochromic spiropyran dye (1,3,3-trimethylindolino-6'-nitrobenzopyrylospiran) (6-nitro BIPS).