PVP-assisted aqueous dispersion of hydrophobic lanthanide complexes for luminescence thermometry

Water-insolubility strongly limits the application of many highly luminescent lanthanide complexes in aqueous environments. Here, we demonstrate a simple polymer-assisted strategy for preparing stable and optically transparent aqueous dispersions of hydrophobic β-diketonate complexes using only a small amount of poly (vinylpyrrolidone) (PVP). Representative Tb(acac) 3 (H 2 O) 2 and Eu(ttfac) 3 (H 2 O) 2 complexes (acac = pentane-2,4-dionate; ttfac = 4,4,4-trifluoro-1-(thiophen-2-yl)butane-1,3-dionate) retained their characteristic photoluminescence and exhibited pronounced temperature-dependent emission in water. The maximum relative thermal sensitivities reached 2.4%∙ o C -1 for Tb(acac) 3 @PVP at 45 °C and 3.9%∙ o C -1 for Eu (ttfac) 3 @PVP at 55 °C. The corresponding minimum estimated temperature resolutions were 0.224 °C and 0.138 °C, respectively. The aqueous processability of the stabilized complexes further enabled the straightforward preparation of dual-emissive Tb 3+ /Eu 3+ systems, providing ratiometric sensitivities of 1.3%–1.7%∙ o C -1 within the physiologically relevant 30 °C–45 °C range. A hybrid Tb (acac) 3 @PVP/Rhodamine 6G system was also demonstrated as an alternative ratiometric platform. The Tb 3+ /Eu 3+ and Tb 3+ /Rhodamine 6G systems yielded minimum temperature resolutions of 0.31 °C and 0.37 °C, respectively. Cytotoxicity studies indicated good biocompatibility of the developed dispersions. These results establish PVP-assisted dispersion as a simple and versatile route toward water-compatible molecular lanthanide thermometers.