Tuning White Light Emission in Dinuclear Phenoxo Bridged Dy^III Complexes

A new series of dinuclear dysprosium(III) complexes, [Dy₂(L^CH)₂(NO₃)₂(MeOH)₂] (I), [Dy₂(L^CH)₂(NO₃)₂(DMF)₂]·2DMF (II), [Dy₂(L^Cl)₂(NO₃)₂(DMF)₂]·2DMF (III), and [Dy₂(L^CH)₂(NO₃)₂(DMF)₂] (IV), with 2,2'-[[(2-pyridinylmethyl)imino]di(methylene)]bis(4-R-phenol), where R = CH₃, Cl, and CH₃O, were investigated as potential white light emitters. All octacoordinated dysprosium(III) are phenoxo-bridged species and have a similar coordination environment. Nevertheless, I has a MeOH ligand molecule, while for II-IV a DMF ligand replaces that of MeOH. The nature of the coordinated solvent molecule plays an important role in the behavior of the thermal dependence of the Y/B (yellow/blue) emission ratio of the Dy^III complexes (Y: ⁴F_9/2 → ⁶H_13/2, yellow and B: ⁴F_9/2 → ⁶H_15/2, blue transitions),, since for I the variation of this ratio is significant, while for the other Dy^III complexes with DMF as ligand the ratio remains constant within experimental error. At room temperature the CIE (Commission International d'Eclairage) color coordinates for the Dy^III complexes, I (0.286, 0.317), III (0.302, 0.324), and IV (0.322, 0.348) are close to the NTSC (National Television System(s) Committee) standard value for white color. Varying the temperature from 16 to 300 K the CIE coordinates for I change from the blueish to white region of the chromaticity diagram, while those of II present an inverse thermal dependence as compared to I. The CCT (Correlated Color Temperature) values at room temperature for I (8384 K), II (17235 K), and IV (5948 K) permit us to consider these complexes as candidates for white cold light emitters, the high value of II being uncommon. For I and II the CCT values vary strongly with temperature, showing a decrease with increasing temperature for I, and an increase with increasing temperature for II, thus making evident the influence on the photophysical properties of the nature of the coordinated solvent molecule in these complexes.