Experimental and density functional theory insights into the effect of withdrawing ligands on the fluorescence yield of Ru(II)‐based complexes

Abstract

The quality of emission spectra of metal complexes gives good insights into their performance in many optoelectronic applications. Herein, the effect of the number and position of various ligand structures on the emission spectra of Ru bipyridine complexes was studied. Specifically, the use of a different number of withdrawing groups (COOH) was investigated in detail. The complexes were first investigated using density functional theory (DFT) and time‐dependent DFT calculations and then confirmed experimentally. The bandgap energy, reactivity, emission spectra and Stokes shift were found to depend on the number and position of the withdrawing groups attached to the Ru(bpy)22+ complexes. Upon increasing the number of withdrawing groups, the electrons were found to be withdrawn from the carbon orbitals and resonated to reach the metal, and accumulated around it, thus enhancing the metal‐to‐ligand charge transfer mechanism instead of the ligand‐to‐ligand charge transfer mechanism. The complexes with more withdrawing groups showed spectra with more intense emission peaks with shorter lifetime, indicating the enhancement in the photoactivity of the complexes. Ligands with ring nitrogens with two COOH groups showed the greatest effect on the enhancement of the emission spectra with a lifetime of 0.5359 ns. The resulting collective emission spectra covered a wide wavelength range, making the investigated complexes a good choice for many optoelectronic applications.