Inorganic–organic hybrid nanoparticles with carbonate-triggered emission-colour-shift

Eu$^{3+}$$_4$[PTC]$^{4-}$$_3$)$_{0.78}$(Eu$^{3+}$[TREN-1,2-HOPO]$^{3+}$)$_{0.22}$ inorganic–organic hybrid nanoparticles (IOH-NPs) contain Eu$^{3+}$, tris[(1-hydroxy-2-oxo-1,2-dihydropyridine-6-carboxamido)ethyl]amine (TREN-1,2-HOPO) and perylene-3,4,9,10-tetracarboxylate (PTC). The IOH-NPs are prepared in water and exhibit a rod-type shape, with a length of 60 nm and a diameter of 5 nm. Particle size and chemical composition are examined by different methods (SEM, DLS, FT-IR, TG, C/H/N analysis). With TREN-1,2-HOPO as antenna, the IOH-NPs show Eu$^{3+}$-based red emission, whereas the PTC emission is totally quenched due to π-stacking in the solid nanoparticles. After addition of carbonate, PTC is released from the IOH-NPs into solution, resulting in an increasing green emission of free PTC. The resulting carbonate-driven shift of the emission colour from red to green surprisingly allows to determine the carbonate concentration qualitatively and quantitatively in a concentration range of 1 μM to 2 mM and was tested for tap water as a specific example.