Self-Assembly of a Two-Dimensional Coordination Polymer Based on Silver and Lanthanide Tetrakis-Acylpyrazolonates: An Efficient New Strategy for Suppressing Ligand-to-Metal Charge Transfer Quenching of Europium Luminescence.

A new strategy for the easy polymerization of anionic [Ln(Qcy)4]- (HQcy-4-(cyclohexanecarbonyl)-5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one) into two-dimensional layers of [AgLn(Qcy)4]n (Ln = Sm, Eu, Gd, Tb and Dy) is proposed by binding the single molecular anions [Ln(Qcy)4]- to silver cations through the coordination of the pyridinic nitrogen atoms of the pyrazolonate rings. The luminescent properties of [AgLn(Qcy)4]n have been studied in detail, and it was shown that the previously described low photoluminescence quantum yield (PLQY) of [Eu(Qcy)4]- is due to Ligand-To-Metal Charge Transfer (LMCT) quenching, which is effectively suppressed in the heterometallic [AgEu(Qcy)4]n polymer. Sensibilization coefficients for H3O[Eu(Qcy)4], [AgEu(Qcy)4]n, and H3O[Sm(Qcy)4] complexes (n ≈ 1) were estimated via theoretical analysis (also by using Judd-Ofelt theory for Sm3+) and PLQY measurements.