Bis(Bipyridyl)-Ru(II)-1-benzoyl-3-(pyridine-2-yl)-1H-pyrazole as potential photosensitiser: Experimental and density functional theory study

Abstract

Ru(II) complexes, [Ru(bpy)2(m-R-L)](PF6)2 where bpy = 2,2’-bipyridyl and m-R-L= 1-(meta-R)-benzoyl-3-(pyridine-2-yl)-1H-pyrazole derivatives (R = H, CH3 and Cl) abbreviated as RuL, Ru(m-CH3-L) and Ru(m-Cl-L) complexes, respectively, were synthesized and characterized with spectroscopic techniques namely, infrared, UV-Vis and nuclear magnetic resonance (NMR), photoluminescence and mass spectroscopy. Density functional theory (DFT) and time-dependent (TD) DFT calculations were carried out to study the structural and electronic features of the molecules. These Ru(II) complexes exhibit photo-electronic properties required for a photosensitiser in a TiO2-catalysed photoelectrochemical (PEC) cell. In-depth understanding of the R-L fragment functionality is important to tune the photo-electronic properties of the Ru(II) complex. The highest-occupied molecular orbital (HOMO) is mainly localized at the Ru(II) centre, while the LUMO is dominantly spread across the R-L ligand. The Ru(II) complexes showed favourable metal-to-ligand charge transfer (MLCT) energy levels, which are comparably higher than the conduction band of TiO2 to facilitate electron injection process. Among the Ru(II) complexes, Ru(m-Cl-L) comparatively possesses the highest photoluminescence quantum yield and has the potential to be applied as photosensitiser in PEC systems.