Hydrophilic
colloids (PSS-[Ln2(TCAi)2]
and PSS-[LnCAi], where i = 1, 2,
or 3 and Ln = Gd or Tb) were prepared by precipitation of
Gd(III) or Tb(III) complexes with tetrathiacalix[4]arenes (TCAi) and calix[4]arenes bearing two 1,3-diketone groups (CAi) from dimethylformamide to an aqueous solution of poly(sodium
4-styrenesulfonate) (PSS). Dynamic light scattering and transmission
electron microscopy demonstrated the formation of nanoparticles coated
by the polymer. Luminescence decay measurements on Tb(III)-based colloids
allowed hydration numbers of 2 and 4 per metal ion to be determined
for PSS-[Ln2(TCAi)2] and PSS-[LnCAi] samples, respectively. Longitudinal and transverse water
proton relaxivity values measured at 20.8 MHz were remarkably high
for the PSS-[GdCAi] colloids but unexpectedly low
for the PSS-[Gd2(TCAi)2] ones. 1H fast field cycling nuclear magnetic resonance relaxometry
was applied to shed light on the origin of the different relaxation
enhancement in the investigated systems. Extremely slow exchange with
the bulk of water molecules coordinated to Gd(III) and the scarce
accessibility of Gd(III) sites to water were highlighted as the main
causes of limited relaxivity.
The report introduces hybrid polyelectrolyte-stabilized colloids combining blue and green-emitting building blocks, which are citrate carbon dots (CDs) and [TbL]+ chelate complexes with 1,3-diketonate derivatives of calix[4]arene. The joint incorporation of green and blue-emitting blocks into the polysodium polystyrenesulfonate (PSS) aggregates is carried out through the solvent-exchange synthetic technique. The coordinative binding between Tb3+ centers and CD surface groups in initial DMF solutions both facilitates joint incorporation of [TbL]+ complexes and the CDs into the PSS-based nanobeads and affects fluorescence properties of [TbL]+ complexes and CDs, as well as their ability for temperature sensing. The variation of the synthetic conditions is represented herein as a tool for tuning the fluorescent response of the blue and green-emitting blocks upon heating and cooling. The revealed regularities enable developing either dual-band luminescent colloids for monitoring temperature changes within 25–50 °C through double color emission or transforming the colloids into ratiometric temperature sensors via simple concentration variation of [TbL]+ and CDs in the initial DMF solution. Novel hybrid carbon dots-terbium chelate PSS-based nanoplatform opens an avenue for a new generation of sensitive and customizable single excited dual-band nanothermometers.
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