具有光致发光性质的铀酰膦酸配位聚合物已经用于温度传感, 但尚未用于双响应发光温度计. 本工作报道了一种基于邻羧基苯甲基膦酸配体(2-pmbH₃)的层状铀酰膦酸配位聚合物, 即(α-C₈H₁₂N)[UO₂(2-pmb)] (1). 其中铀酰离子通过2-pmb³⁻配体连接成层, 外消旋且质子化的苯乙胺分子作为抗衡离子占据层间. 层内最近的U1···U1距离为0.541 nm. 化合物1表现出较高的热稳定性和水稳定性. 光致发光性质表明, 化合物1在室温下发出绿光, 可以在200~360 K的温度范围内作为发光强度和寿命的双响应发光温度计, 其强度依赖的最大灵敏度为2.96%•K⁻¹ (330 K), 寿命依赖的最大灵敏度为2.51%•K⁻¹ (350 K), 实现了工作温度更高、灵敏度更高的铀酰基温度计. 相对论密度泛函(DFT)计算证实了该化合物的稳定性来源于铀酰赤道面膦酸氧2p轨道与铀5f_ϕ轨道相互作用. 计算表明, 在320 nm和412 nm附近的两个峰为O=U=O内氧以及膦酸氧2p到铀5f_δ (f_z(x2−y2))的配体到金属电荷转移(LMCT).

Luminescent uranyl phosphonate coordination polymers have been used for temperature sensing but have not yet been used for dual-response luminescence thermometers. Herein we report a luminescent uranyl phosphonate based on 2-(phosphonomethyl)benzoic acid (2-pmbH₃), namely, (α-C₈H₁₂N)[UO₂(2-pmb)] (1). This compound crystallizes in monoclinic space group C2/c and shows a layered structure. Within the layer, the uranyl ions are doubly bridged by O—P—O and O—C—O unis forming chains. The equivalent chains are cross-linked through corner-sharing of UO₇ pentagonal bipyramids and PO₃C tetrahedra forming a layer. The adjacent U···U distances within the layer are 0.5414 and 0.5743 nm. The organic groups of the 2-pmb³⁻ ligand reside on the two sides of the layer. The interlayer space is filled with the racemic protonated phenethylamine cations to charge-balance the anionic layer. The shortest U···U distance between the layers is 1.239 nm. Compound 1 exhibits high thermal and water stability, especially in aqueous solution at pH 5~11 and in boiling water. The UV-Vis spectrum of 1 shows two broad bands peaking at 320 and 412 nm. The scalar-relativistic density functional calculations reveal that the two bands are associated with ligand-to-metal charge transfer (LMCT) transitions from ligand orbitals to metal orbitals lower-f_δ (f_z(x2−y2)). Photoluminescence properties show that 1 emits green-light at room temperature with six emission peaks at 481, 500, 516, 540, 564 and 591 nm, assigned to the electronic and vibronic transitions of S₁₁-S₀₀ and S₁₀-S_0ν (ν=0~4). Interestingly, both the emission intensity and the lifetime of compound 1 are temperature-dependent, making it possible to be used as a dual-response luminescence thermometer in the temperature range of 200~360 K. The intensity-dependent maximum sensitivity is 2.96%•K⁻¹ (330 K) and the lifetime-dependent maximum sensitivity is 2.51%•K⁻¹ (350 K), which are comparable to some lanthanide-based luminescent thermometers. This work provides a rare example of uranyl coordination polymers that can be used as a dual-response luminescence thermometer with wide operating temperature and good sensitivity.