An Europium (III) Luminophore with Pressure-Sensing Units: Effective Back Energy Transfer in Coordination Polymers with Hexadentate Porous Stable Networks

Abstract

A luminescent Eu^III coordination polymer with O₂ -sensing units under air, Eu^III -hcpt (hcpt: 2,3,6,7,10,11-hexakis(4-carboxy-phenyl)triphenylene), is reported. The hexadentate carboxylic acids in hcpt ligands play an important role in the formation of tight-packed three-dimensional networks in Eu^III -hcpt, giving hyper thermo-stable structures (decomposition temperature=420 °C). The three-dimensional porous network promotes bright luminescence (4f-4f emission quantum yield=70 %). The emission lifetime of Eu^III -hcpt under vacuum (0.86 ms) was twice as large as that under O₂ (0.48 ms, 1 atom:101.3 kPa). The Arrhenius analysis of the emission decay profile indicates that the back energy transfer (BEnT) from the emitting level of the europium(III) ion to the excited T₁ state of the hcpt ligand should be activated at room temperature. The gradual decrease of emission lifetime is caused by the BEnT process in Eu^III -hcpt. Finally, an advanced pressure-sensitive luminophore is demonstrated.

Keywords: coordination polymer; energy transfer; europium; luminescence; oxygen sensor.