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

Abstract

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).

A Three-Component Donor–Acceptor Hybrid Framework with Low-Power X-ray-Induced Photochromism

“…In addition, there are plenty of supramolecular interactions (Figures S7 and S8), such as anion−π interactions, O–H···N H-bonds, C–H···N H-bonds, O–H···O H-bonds, among [Co­(CN) 6 ] 3– anions, free or/and coordinated H 2 O molecules, and bcbp ligands in the D–A hybrid architecture, which consolidate the D–A hybrid structure. Moreover, the anion−π interactions between Co­(CN) 6 3– anions and bcbp ligands in the D–A hybrid architecture may provide electron-transfer pathways to realize the reversible dual photochromism. ,,,− …”

“…These distances are also comparable to those in previously reported X-ray and UV dual photochromic compounds. 20,22,25 Such strong anion−π interactions between donors and acceptors may come from the tight packing of the Co(CN) 6 3− ions (with diameter of ∼7.5 Å) inside the small pores (with a cavity size of ∼7.6 nm) of interpenetrated 3D architecture. Therefore, the compact stacking mode between Co(CN) 6 3− ions and europium viologen frameworks leads to strong anion−π interactions and appropriate distances between donors and acceptors, which finally give rise to the obvious Xray and UV dual photochromic behaviors.…”

“…Photochromic materials usually exhibit reversible and visible color changes upon exposure to external light sources and have become an active research area in the past several years. Among them, considerable effort has been devoted to exploring ultraviolet (UV) or visible light-induced photophysical properties such as photomagnetism, photoconductance, and photoluminescence as well as applications in the field of erasable printing and smart windows. , However, the development of X-ray-induced photochromic materials is still in infancy. − At present, the scintillation counters, ionization gauges, and other devices have been developed for X-ray detection. − However, X-ray-sensitive materials used in these devices often require electronic attachments or tedious operations to process the signals. − Compared to commercial X-ray-sensitive materials, donor–acceptor (D–A) hybrid materials with organic and inorganic photoactive moieties fabricated at the molecular level make up an emerging class of photochromic materials that can be directly “visualized” by X-ray irradiation. − Although a few D–A hybrid materials with X-ray-induced photochromism (XIP) have been reported, most of them are produced in high-power environments, − and it is still rather rare for those with low-power XIP. , Accordingly, developing new radiosensitive D–A hybrid materials that can directly show a color change upon low-power irradiation with convenient operation is meaningful.…”

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

“…21–23 In addition, we have recently developed a series of radiochromic or fluorochromic terpyridine-containing MOFs and clusters, which can withstand a radiation dose up to 1 MGy. 24–27 However, dosimeters based on these state-of-the-art materials remain a small group and are worth further exploration.…”

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

“…13 Furthermore, coordination polymers or cluster species showing radiochromism, radiophotoluminescence, uorochromism, and photoluminescence quenching upon accumulated doses of ionizing radiation have been documented, making them as promising candidates of radiation dosimeters. [19][20][21][22][23][24][25][26] Notably, the abundance of luminescent centers or radio-responsive moieties in some of these materials renders higher saturation point in response to radiation dose. This attribute allows for wider operation ranges or higher upper limits of detection compared with those of traditional metal-ion-doped inorganic dosimeters, e.g.…”