Tunable white-light emission from mixed lanthanide (Eu3+, Gd3+, Tb3+) coordination polymers derived from 4-(dipyridin-2-yl)aminobenzoate

Abstract

Herein, we have developed a series of isostructural mixed Ln³⁺-4-(dipyridin-2-yl)aminobenzoate coordination polymers [Ln³⁺ = Eu³⁺ (1), Tb³⁺ (2), and Gd³⁺ (3)], and characterized and investigated their photophysical properties. The results demonstrated that by gently tuning the excitation wavelength of these mixed lanthanide complexes, white light emission can be realized with the Commission Internationale de I'Eclairage coordinates (0.32, 0.34). Furthermore, by changing the concentration profiles of lanthanide ions stoichiometrically in mixed-lanthanide complexes and exciting at particular wavelengths, various emission colours can also be successfully obtained. The antenna ligand, 4-(dipyridin-2-yl)aminobenzoic acid, provides an efficient energy transfer for the sensitization of Eu³⁺ and Tb³⁺ complexes and exhibits red and green emissions, respectively. Most importantly, due to the high energy (32 150 cm⁻¹) of the Gd³⁺ ion lowest-lying emission level, the corresponding Gd³⁺ complex displays ligand-centered visible emission in the blue light region, and hence it acts as a blue emitter. Therefore, Eu³⁺ and Tb³⁺ complexes in conjunction with a Gd³⁺ complex is a suitable choice to obtain tunable white-light-emission from Ln³⁺ coordination polymers. The morphological analyses of the mixed lanthanide coordination polymers by transmission electron microscopy (TEM) disclose that these compounds exist as unique crystalline nano-rods with an average diameter of 200 nm. The developed mixed lanthanide complexes also exhibit high thermal stability (∼420 °C).