Huangjie Lu,Zhaofa Zheng,Zi-Jian Li,Hongliang Bao,Xiaojing Guo,Xiaofeng Guo,Jian Lin,Yuan Qian,Jian-Qiang Wang
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 new multifunctional ionic liquid-based metal–organic hybrid (PMAIL) was synthesized by anion exchange between as-synthesized phosphonate-based ionic liquid and phosphomolybdic acid and applied to epoxy resin (EP) as an efficient flame retardant. As expected, with only 1 wt% addition of PMAIL, the char yield of EP-PMAIL1 composite at 700 °C was significantly improved by 108.3% from 12.0% for neat epoxy resin to 25.0%, demonstrating the outstanding catalytic charring effect of PMAIL. Meanwhile, EP-PMAIL6 composite (6 wt% addition) can reach V-0 rating in the UL-94 vertical burning tests easily, and its peak heat release rate and total smoke production of EP-PMAIL6 were dropped by 31.0 and 15.4%, respectively, compared with neat EP. Moreover, the results from cone calorimetry tests showed that the char yield of EP-PMAIL6 was enhanced by 162% from 9.5 to 24.9% compared with neat EP, resulting in a strong intumescent char layer structure with outstanding fire retardance and mechanical properties. The thermo-oxidative stable protective layer retarded the transfer of heat and flammable volatiles during combustion and protected the epoxy matrix from further degradation. In conclusion, our results might provide a new perspective for producing composites with excellent flame retardancy and smoke suppression properties using ionic liquid-based metal–organic hybrid.
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