Fluorescent Zinc(II) Thione and Selone Complexes for Light-Emitting Applications

Abstract

Three 1-(anthracene-9-ylmethyl)-3-isopropyl-imidazol-2-thione Zn(II) halide complexes (1-3), and one 1-(anthracene-9-ylmethyl)-3-isopropyl-imidazol-2-selone Zn(II) dichloride complex (4) have been synthesized and characterized. Complexes 2, 3, and 4 have distorted tetrahedral geometry, while complex 1 has tetrahedral geometry. All these complexes displayed emission in the crystalline state, with complex 3 showing emission in the yellow region and 1 and 4 in the blue, while 2 gave bluish-green emission. The ligands L1 and L2 were non-emissive in both solution and crystalline state. The photophysical behavior of these four complexes was studied and the quantum yield in crystalline state was obtained. Complex 1 gave the highest quantum yield of 7.72% and 2 and 3 gave 5.95%, and 5.07% respectively. Complex 4 has a relatively lesser quantum yield (3.87%). The crystalline state quantum yield for the complexes varies with the variation of the halide coordinated to the metal center as Clˉ > Brˉ > Iˉ. The quantum yield for the thione complexes 1-3 is found to be better than the selone complex 4. Density functional theory calculations have been performed to study their structural properties and emissive natures. TD-DFT natural transition orbital calculations reveal that intra-ligand charge transfer (1ILCT) mediated through the metal center is responsible for the observed emission behavior.