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.