Intensity and lifetime ratiometric luminescent thermometer based on a Tb(iii) coordination polymer

A three-dimensional terbium(III) coordination polymer of formula [Tb(bttb)(0.5)(2,5-pzdc)(0.5)](n) (1) [H(4)bttb = 1,2,4,5-tetrakis(4'-carboxyphenyl)benzene and H-2-2,5-pzdc = 2,5-pyrazinedicarboxylic acid] was obtained under hydrothermal conditions. The bttb(4-) tetraanion in 1 adopts the bridging and chelating-bridging pseudo-oxo coordination modes while the 2,5-pzdc(2-) dianion exhibits a rather unusual bis-bidentate bridging pseudo-oxo coordination mode, both ligands being responsible for the stiffness of the resulting 3D structure. Solid-state photoluminescent measurements illustrate that 1 exhibits remarkable green luminescence emission, the most intense band occurring in the region of 550 nm (D-5(4) -> F-7(5)) with lifetimes at the millisecond scale. Thermometric performances of 1 reveal a maximum relative sensitivity (S-m) of 0.76% K-1 at 295 K (delta T = 0.05 K), constituting a Tb-III ratiometric solid luminescent thermometer over the physiological temperature range. Variable-temperature static (dc) magnetic susceptibility measurements for 1 in the temperature range 2.0-300 K show the expected behavior for the depopulation of the splitted m(J) levels of the F-7(7) ground state of the magnetically anisotropic terbium(III) ion plus a weak antiferromagnetic interaction through the carboxylate bridges. No significant out-of-phase magnetic susceptibility signals were observed for 1 in the temperature range 2.0-10.0 K, either in the absence or presence of a static dc magnetic field.