层状铀酰膦酸配位聚合物作为双响应光致发光温度计

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 mono-clinic 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-fδ (fz(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-S0ν (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.