Eu-Based Phosphorescence Lifetime Polymer Nanothermometer: A Nanoemulsion Polymerization Approach to Eliminate Quenching of Eu Emission in Aqueous Media

In this work, we report on the synthesis of the two highly thermosensitive Eu complexes ([(tta)3Eu(NN1)] (Eu1) and [(tta)3Eu(NN2)] (Eu2), where tta is thenoyltrifluoroacetone, NN1 is 3-phenyl-2-(pyridin-2-yl)pyrido[2,1-a]pyrrolo[3,2-c]isoquinoline, and NN2 is 1-phenyl-2-(pyridin-2-yl)-1H-phenanthro[9,10-d]imidazole), and preparation of luminescent thermosensitive nanomaterial (latex nanothermometer, LNT). LNT design and preparation were based on the application of Eu2 and copolymerization of butyl and methyl methacrylates in the presence of the complex, surfactant (cetyltrimethylammonium bromide), and cosurfactant (acetone). Optimization of nanoemulsion polymerization conditions allowed us to obtain strongly luminescent nanoparticles with a narrow size distribution (D = 75 nm; PDI = 0.05). Moreover, the resulting LNT particles feature nonuniform distribution of Eu2, which localizes mainly inside the nanoparticles while the outer layer lacks the complex. As a result, the developed LNT demonstrates monoexponential luminescence decays with a lifetime temperature sensitivity up to 0.84%/K and resolutions of 0.26 K comparable to or exceeding existing analogues together with complete reversibility in cycling experiments.