Fine-Tuning X-Ray Sensitivity in Organic-Inorganic Hybrids via an Unprecedented Mixed-Ligand Strategy.

Crystalline organic-inorganic hybrids, which exhibit colorimetric responses to ionizing radiation, have recently been recognized as promising alternatives to conventional X-ray dosimeters. However, X-ray-responsive organic-inorganic hybrids are scarce and the strategy to fine-tune their detection sensitivity remains elusive. Herein, an unprecedented mixed-ligand strategy is reported to modulate the X-ray detection efficacy of organic-inorganic hybrids. Deliberately blending the stimuli-responsive terpyridine carboxylate ligand (tpc- ) and the auxiliary pba- group with different ratios gives rise to two OD thorium-bearing clusters (Th-102 and Th-103) and a 1D coordination polymer (Th-104). Notably, distinct X-ray sensitivity is evident as a function of molar ratio of the tpc- ligand, following the trend of Th-102 > Th-103 > Th-104. Moreover, Th-102, which is exclusively built from the tpc- ligands with the highest degree of π-π interactions, exhibits the most sensitive radiochromic and fluorochromic responses toward X-ray with the lowest detection limit of 1.5 mGy. The study anticipates that this mixed-ligand strategy will be a versatile approach to tune the X-ray sensing efficacy of organic-inorganic hybrids.

Incorporating Photochromic Viologen Derivative to Unprecedentedly Boost UV Sensitivity in Photoelectrochromic Hydrogel.

Developing ultraviolet (UV) radiation sensors featuring high sensitivity, ease of operation, and rapid readout is highly desired in diverse fields. However, the strategies to enhance sensitivity of UV detection remain limited particularly for photochromic materials, which show colorimetric response toward UV irradiation. Guided by our initial goal of facilitating easier handling, we formulated a viologen derivative ([H2L]-SC) incorporating hydrogel-based UV sensor which not only inherits the photochromism of [H2L]-SC but also engenders an unprecedented reversible photoelectrochromic response that is absent in either [H2L]-SC or hydrogel alone. Judicious synergy between photochromic [H2L]-SC and polyacrylamide (PAM) converts the colorimetric response of [H2L]-SC into the electrical resistance change of [H2L]-SC@PAM, which amplifies the UV sensitivity of [H2L]-SC by 2 orders of magnitude. Explicitly, the limit of detection (LOD) for UV decreases from 296.3 mJ/cm2 based on the UV-vis absorption spectra of [H2L]-SC to 2.83 mJ/cm2 derived from the resistance variation of [H2L]-SC@PAM. Moreover, linear correlation between the resistance reduction rate of [H2L]-SC@PAM and UV dose rate can be established, rendering it as a dual platform for quantifying both the accumulated UV dose and the instant dose rate. In addition, the proposed strategy based on constructing photoelectrochromic hybrids offers a new pathway to boost the UV sensitivity that could be universal for other photochromic materials.

A robust thorium-organic framework as a bifunctional platform for iodine adsorption and Cr(VI) sensitization.

Simple synthetic modulation based on thorium nitrate and tris((4-carboxyl)phenylduryl)amine (H3TCBPA) gives rise to a new thorium-based metal-organic framework, Th-TCBPA, which features excellent hydrolytic and thermal stabilities. Incorporating electron-rich TCBPA3- linkers not only endows Th-TCBPA with high adsorption capacity toward radioiodine vapor, but also makes it a luminescence sensor for the highly sensitive and selective detection of Cr(VI) anions.

Stepwise Crystallization of Millimeter Scale Thorium Cluster Single Crystals as a Bifunctional Platform for X-ray Detection and Shielding.

Monitoring and shielding of X-ray radiation are of paramount importance across diverse fields. However, they are frequently realized in separate protocols and a single material integrating both functions remained elusive. Herein, a hexanuclear cluster [Th6 (µ3 -OH)4 (µ3 -O)4 (H2 O)6 ](pba)6 (HCOO)6 (Th-pba-0D) incorporating high-Z thorium cations and 3-(pyridin-4-yl)benzoate ligands that can function as a brand-new dual-module platform for visible detection and efficient shielding of ionizing radiation is demonstrated. Th-pba-0D exhibits rather unique reversible radiochromism upon alternating X-ray and UV irradiation. Moreover, the millimeter scale crystal size of Th-pba-0D renders the penetration depth of X-ray visible to naked eye and leads to the unearthing of its high X-ray attenuation efficiency. Indeed, the shielding efficacy of Th-pba-0D is comparable to that of lead glass containing 40% PbO, and a Th-pba-0D pellet with a thickness of merely 1.2 mm can shield 99.73% X-ray (16 keV). These studies portend the possible utilization of thorium-bearing materials as a bifunctional platform for radiation detection and shielding.

Enhancing photosensitivity via the assembly of a uranyl coordination polymer.

Synergistic assembly of uranyl centres and luminescent 2,6-bis(pyrazol-1-yl)pyridine-4-carboxylates (bppCOOH) gives rise to a uranyl coordination polymer, namely U-bppCOO, which exhibits a luminescence quenching response toward UV or X-ray irradiation doses. Notably, the photosensitivity of U-bppCOO has been significantly enhanced via metal-ligand assembly compared with that of the naked bppCOOH ligand.

Luminometric dosimetry of X-ray radiation by a zwitterionic uranium coordination polymer.

A novel X-ray dosimeter based on a uranium coordination polymer U-Cbdcp was obtained by the judicious synergy between the luminescent uranyl centres and zwitterionic tritopic ligands. Notably, U-Cbdcp exhibits luminescence quenching upon increasing X-ray dose, which in combination with its excellent radiolytic stability, makes it suitable for X-ray dosimetry.

Unveiling the new function of uranyl molecular clusters as fluorometric sensors for UV and X-ray dosimetry.

Simple synthetic modulation based on uranyl acetate and phenanthroline has resulted in two uranyl clusters (1 and 2) with different topologies and nuclearities. Notably, the dimeric complex exhibits distinct luminescence quenching upon UV and X-ray irradiation with detection limits of 4.30 × 10-6 J and 0.32 Gy, respectively. To advance the practical application, 1 was further fabricated with polyvinylidene fluoride into a flexible strip as a UV and X-ray indicator.

A New Concept of Radiation Detection Based on a Fluorochromic and Piezochromic Nanocluster.

Developing materials that possess colorimetric responses to external stimuli is a promising strategy for addressing the current challenges in radiation dosimetry. Currently, colorimetric ionizing-radiation-responsive materials remain underexplored, and those with multistimuli response are rare. Herein, the integration of thorium cation and photoresponsive terpyridine carboxylate ligand gives rise to a thorium nanocluster, Th-101, which displays the second case of fluorochromic response and unprecedented piezochromic behavior among all actinide materials. The emission color of Th-101 exhibits a gradual transition from blue to cyan to green upon irradiation with accumulated dose, which renders colorimetric dosimetry of ionizing radiation based on a red-green-blue (RGB) concept. Further fabricating Th-101 into a custom-built optoelectronic device allows for on-site quantification of radiation dose with merits of ease of operation, rapid readout, and cost-effectiveness.

Emergence of Thorium-Based Polyoxo Clusters as a Platform for Selective X-ray Dosimetry.

A brand-new application of thorium-bearing clusters in the field of ionizing radiation detection is exemplified by two novel hexanuclear thorium clusters, Th-bppCOO-1 and Th-bppCOO-2, which incorporate carboxylate-functionalized 2,6-di(pyrazol-1-yl)pyridine ligands. Notably, Th-bppCOO-1 is composed of an unprecedented [Th6(OH)4O4(H2O)5]12+ secondary building unit, the Th6 core of which is decorated by five H2O molecules. Furthermore, selective photoluminescence quenching responses of Th-bppCOO-1 and Th-bppCOO-2 toward X-ray over UV radiation have been demonstrated for the first time.

Achieving colour tuneable and white-light luminescence in a large family of dual-emission lanthanide coordination polymers.

Expanding the family of lanthanide terpyridine coordination polymers has yielded eighteen new complexes with two different phases, Ln(TPC)2(HCOO)(H2O) (Ln-1) and Ln(TPC)(HCOO)2 (Ln-2) (Ln = Sm-Lu, except Tm). Both structures are composed of lanthanide cations interconnected by 2,2':6',2''-terpyridine-4'-carboxylate ligands to yield one-dimensional chain topologies. However, the incorporation of an additional crystallographically unique decorative TPC ligand into Ln-1 gives rises to a distinct phase. The encapsulation of both metal- and ligand-based phosphors within single coordination polymers leads to dual-emission of the afforded materials. Furthermore, judicious lanthanide doping in heterometallic Ln-1 and Ln-2 allows for fine-tuning the photoluminescent colours over a wide range of gamut. Such a combination showcases the capability to fine-tune the emission colours from deep green, to red, and to blue. In addition, direct white-light emission upon UV excitation can be achieved in the SmxGd1-x-1 system.

Emergence of a thorium-organic framework as a radiation attenuator for selective X-ray dosimetry.

By first applying a thorium-organic framework (Th-SINAP-2) as a radiation attenuator and by incorporating a terpyridine derivative (Htpbz) as a photo-responsive guest, selective photochromism in response to X-rays was achieved in the host-guest assembly of Htpbz@Th-SINAP-2. Such a combination endows the afforded material with the lowest detection limit of X-ray dose among all photochromic sensors and a brand-new function of X-ray dosimetry for thorium containing materials.

Achieving UV and X-ray Dual Photochromism in a Metal-Organic Hybrid via Structural Modulation.

Rational design and synthesis of new photochromic sensors have been active research areas of inquiry, particularly on how to predict and tailor their properties and functionalities. Herein, two thulium 2,2':6',2''-terpyridine-4'-carboxylate (TPC)-functionalized metal-organic hybrids, Tm(TPC)2(HCOO)(H2O) (TmTPC-1) and Tm(TPC)(HCOO)2 (TmTPC-2) with different photochromic response behaviors, have been successfully prepared, allowing for straightforward investigations of the structure-property correlation. Single-crystal X-ray diffraction and electron paramagnetic resonance analyses revealed that the incorporation of a unique dangling decorating TPC unit in TmTPC-1 offers a shorter and more accessible π-π interaction pathway between the adjacent TPC moieties than that in TmTPC-2. Such a structural feature leads to the production of radical species via a photoinduced intermolecular electron-transfer (IeMCT) process upon UV or X-ray irradiation, which ultimately endows TmTPC-1 with a rather unusual UV and X-ray dual photochromism. A linear relationship between the change of UV-vis absorbance intensity and X-ray dose was established, making TmTPC-1 a promising dosimeter for X-ray radiation with an extremely high energy threshold (30 kGy). To advance the development for real-world application, we have fabricated polyvinylidene fluoride (PVDF) membranes incorporating TmTPC-1 for functioning either as a UV imager or as an X-ray radiation indicator. Lastly, TmTPC-1 exhibits high thermal stability (up to 400 °C) and radioresistance (at least 900 kGy), and also excellent reversibility of photochromic transformation (at least 5 cycles).

Tuning of the Network Dimensionality and Photoluminescent Properties in Homo- and Heteroleptic Lanthanide Coordination Polymers.

Targeted synthesis, through a heteroleptic methodology, has resulted in three types of lanthanide (Ln) coordination polymers (CPs) with tailored dimensionality, tunable photoluminescent colors, and distinct luminescence quenching upon UV and X-ray irradiation. The homoleptic Ln(tpbz)(NO3)2 [CP-1; tpbz = 4-(2,2':6',2″-terpyridin-4'-yl)benzoate] is assembled from Ln cations and bridging tpbz ligands, accompanied by the decoration of NO3- anions, forming a one-dimensional (1D) chain structure. The presence of ancillary dicarboxylate linkers, 1,4-benzenedicarboxylate (bdc) and 2,5-thiophenedicarboxylate (tdc), promotes additional bridging between 1D chains to form a two-dimensional layer and a three-dimensional framework for Ln(tpbz)(bdc) (CP-2) and Ln(tpbz)(tdc) (CP-3), respectively. The multicolor and luminescence properties of the obtained CPs were investigated, displaying typical red EuIII-based and green TbIII-based emissions. The SmIII-bearing CP-1-CP-3, however, exhibit diverse ratiometric LnIII- and ligand-based emissions, with the photoluminescent colors varying from pink to orange to cyan. Notably, the TbIII-containing CP-1-CP-3 display distinct luminescence quenching upon continuous exposure to UV and X-ray irradiation. To our best knowledge, CP-2-Tb represents one of the most sensitive UV dosage probes (3.2 × 10-7 J) among all CPs.