Long‐Range LMCT Coupling in EuIII Coordination Polymers for an Effective Molecular Luminescent Thermometer**

Abstract A design for an effective molecular luminescent thermometer based on long‐range electronic coupling in lanthanide coordination polymers is proposed. The coordination polymers are composed of lanthanide ions EuIII and GdIII, three anionic ligands (hexafluoroacetylacetonate), and a chrysene‐based phosphine oxide bridges (6,12‐bis(diphenylphosphoryl)chrysene). The zig‐zag orientation of the single polymer chains induces the formation of packed coordination structures containing multiple sites for CH‐F intermolecular interactions, resulting in thermal stability above 350 °C. The electronic coupling is controlled by changing the concentration of the GdIII ion in the EuIII‐GdIII polymer. The emission quantum yield and the maximum relative temperature sensitivity (Sm) of emission lifetimes for the EuIII‐GdIII polymer (Eu:Gd=1:1, Φtot=52 %, Sm=3.73 % K−1) were higher than those for the pure EuIII coordination polymer (Φtot=36 %, Sm=2.70 % K−1), respectively. Enhanced temperature sensing properties are caused by control of long‐range electronic coupling based on phosphine oxide with chrysene framework.