Fine‐Tuning X‐Ray Sensitivity in Organic–Inorganic Hybrids via an Unprecedented Mixed‐Ligand Strategy

Abstract 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.

Fine-Tuning X-ray Sensitivity in Organic-Inorganic hybrids via an Unprecedented

Materials and Synthesis
Caution! Caution!Th-232 used in this study is an emitter with the daughter of radioactive Ra-228.All of the thorium compounds used and investigated were operated in an authorized laboratory designed for actinide element studies.Standard protections for radioactive materials should be followed.

Characterizations
Crystallographic Analysis.Single crystal X-ray diffraction measurements were performed using a Bruker D8-Venture single crystal X-ray diffractometer equipped with an IμS 3.0 microfocus X-ray source (Mo-Kα radiation,  = 0.71073Å) and a CMOS detector at 298 K.
The data frames were collected using the program APEX3 and processed using the program SAINT routine in APEX3.The structures were solved by the direct method and refined on F 2 by full-matrix least-squares methods using SHELXTL-2014 program. [1]Powder X-ray diffraction (PXRD) data were collected from 5 to 50° with a step of 0.02° and the time for data collection was 0.5 s on a Bruker D8 Advance diffractometer with Cu Kα radiation (λ=1.54056Å) and a Lynxeye one-dimensional detector.
UV-Vis and Photoluminescence Spectroscopy.The solid-state UV-Vis absorption of single crystals of Th-102, Th-103, and Th-104 were recorded on a Craic Technologies microspectrophotometer. Crystals were placed on quartz slide, and data was collected after auto-set optimization.The photoluminescence spectra of bulk samples were collected on an Edinburgh Instruments FS5 steady state spectrofluorometer with 325 nm UV excitation.The real-time photoluminescence spectra of a single crystal of Th-102 in response to X-ray were recorded on a Craic Technologies microspectrophotometer.When the 365 nm excitation light was selected, an optical filter masking signal below 420 nm was applied in order to mask the interference of excitation light.The sources of X-ray were provided by a W Kα radiation source (60 kV, 12W).The decay curves of bulk samples were collected on an Edinburgh Instruments FLS 980 spectrometer.PL quantum-yield (PLQY) was recorded using a HORIBA scientific Fluorolog-3 spectrophotometer with a quantum-yield accessory.
Fourier Transform Infrared Spectroscopy.The IR spectra were recorded using a FTIR spectrometer (Thermo Nicolet 6700 spectrometer) equipped with a diamond attenuated total reflectance (ATR) accessory in the range of 400-4000 cm −1 .

Electron Paramagnetic Resonance (EPR) Study.
The EPR measurements were performed on a JEOL-FA200 spectrometer at X-band with 100-kHz field modulation.The EPR spectra of nonirradiated and irradiated samples were recorded at room temperature and the microwave power used was 1.0 mW.MeV), and a 60 Co irradiation source (2.22×10 15 Bq), respectively.Th-102, Th-103, and Th-104 were irradiated with accumulated doses with dose rates of 80 mW cm -2 , 150 kGy h -1 , and 11.8 kGy h -1 for UV, EB, γ-ray, respectively.PXRD and FTIR analyses on the irradiated samples were performed to confirm the radiation resistance of Th-102, Th-103, and Th-104.

Hirshfeld Surface Analysis
The SC-XRD structures of Th-102, Th-103, and Th-104 was directly used in the Hirshfeld surface analysis.Hirshfeld surfaces of the selected tpc -ligands were calculated in CrystalExplorer17.5.The two-dimensional fingerprint plots were generated as shown in Stability.The radiation resistance of Th-102, Th-103, and Th-104 were examined by irradiating the powdery sample with UV, EB, or γ-ray irradiation.The sources of UV, EB, and γ-ray were provided by a LED light (365 nm, 25 W), an electron accelerator (1.2

Figure S2 .
Figure S2.The bleaching process by storing the crystal of Th-102 in dark for 2 days.

Figure S3 .
Figure S3.The photoluminescence spectrum of Htpc under 325 nm UV excitation.

Figure S5 .
Figure S5.The micrographs of Th-103 and Th-104 before and after X-ray irradiation.

Figure S6 .
Figure S6.(a) The time-dependent luminescence spectra of a Th-102 upon X-ray irradiation.(b) The time-dependent luminescence spectra of a Th-103 upon X-ray irradiation.(c) The time-dependent luminescence spectra of a Th-104 upon X-ray irradiation.(d) The ratio between the excimer and monomer emission (I G /I B ) as a function of X-ray dose for Th-102, Th-103, and Th-104.

Figure S7 .
Figure S7.The excitation and wavelength-dependent luminescence spectra of a Th-102.

Figure S8 .
Figure S8.The linear correlation between the luminescence intensity at 510 nm and the radiation dose in low dose range.The linear domain in low dose range can be fitted as y = 156.63x + 1076.95where y is the luminescence intensity at 510 nm and x is the radiation dose.The standard deviation (σ) is the standard error of the luminescence measurement, as determined by the baseline measurement of blank samples at 510 nm.If defining three times of the standard deviation as the detectable signal, the detection limit can be projected as 3σ/slope = 3 × 0.07931 /156.63 = 1.5 mGy.

Figure S9 .
Figure S9.The FTIR spectra of Th-102 before and after irradiation with UV, γ-ray, and EB radiation.

Figure S10 .
Figure S10.The FTIR spectra of Th-103 before and after irradiation with UV, γ-ray, and EB radiation.

Figure S11 .
Figure S11.The FTIR spectra of Th-104 before and after irradiation with UV, γ-ray, and EB radiation.

Figure S13 .
Figure S13.Powder X-ray diffraction patterns of Th-102 treated with different RH conditions.

Figure S14 .
Figure S14.Powder X-ray diffraction patterns of Th-103 treated with different RH conditions.

Figure S15 .
Figure S15.Powder X-ray diffraction patterns of Th-104 treated with different RH conditions.

Figure S17 .
Figure S17.The fingerprint plots and relative contributions of different intermolecular contacts to the Hirshfeld surface areas for Th-102.

Figure S18 .
Figure S18.The fingerprint plots and relative contributions of different intermolecular contacts to the Hirshfeld surface areas for Th-103.

Figure S19 .
Figure S19.The fingerprint plots and relative contributions of different intermolecular contacts to the Hirshfeld surface areas for Th-104.

Table S1 .
Crystallographic data of Th