Homometallic Ln(iii)-complexes from an ILCT ligand with sensitized vis-NIR emission, excitation-dependent PL color tuning and white-light emission

Abstract

A facilely available zwitterionic ligand, 1,1′-(1,4-phenylenebis(methylene))dipyridin-4(1H)-one (PBPO), has been designed to bear intraligand charge transfer (ILCT) energy states. PBPO was used to assemble two series of Ln(III) complexes with either 2D (6,3)-hcb network (LIFM-24(Ln), Ln = Pr, Nd, and Sm), or 1D loop-and-chain (LIFM-25(Ln), Ln = Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb) polymeric structures, as determined by the radius of the lanthanide ions. Highly efficient photoluminescence (PL) in the visible to near-infrared (NIR) regions can be obtained in these Ln-complexes, due to the extended energy transfer from both the triplet and ILCT states of the zwitterionic ligand. Among these complexes, LIFM-24(Pr) and LIFM-25(Dy) display excitation-dependent color tunable luminescence and white-light emission based on the combination of ligand-centered (LC) and metallic-centered (MC) emissions. Uniquely, a strict linear relationship was established between the excitation wavelength and the emission CIE (Commission Internationale de L'Eclairage) coordinates in a wide color range (orange to blue for LIFM-24(Pr), and yellow to blue for LIFM-25(Dy)), thereby providing prototype models for programmable PL color tuning and white-light emission, which are rarely achievable in homometallic Ln-complexes.