Quantum Mechanics Investigation of the Photophysical Properties of Ruthenium(II)-Based Complexes Combined with the Development of their Force Field Parameters Using Molecular Mechanics and Molecular Dynamics Simulation

Abstract

The focus of this study is to develop a theoretical strategy that can help guide the design of novel organometallics with desirable photophysical properties for molecular engineering. This computational study includes proposed complexes and others for which experimental data are available. The agreement between the computational results and the experimental observations confirms the validity of our procedure and the level of theory we applied in this study. The ground singlet (S0) and excited triplet (T1) electronic states and corresponding optical spectra of a series of cationic complexes —[RuH(CO)L(PPh3)2]+ (L=2,2´-bipyridyl) (Rubpy), 4,4´-dicarboxylic-2,2´-bipyridyl (Rudcbpy), bis-4,4’-(N-methylamide)-2,2´-bipyridyl (Rudamidebpy), bis-4,4’-(methyl)-2,2´-bipyridyl (RudMebpy), [Ru(CO)2dcbpy(PPh3)2]2+ (Ru(2CO)dcbpy), [Ru(H)2dcbpy(PPh3)2] (Ru(2H)dcbpy), and a series of cationic complexes [RuLL(phen)(PPh3)2]+ (phen= 1,10-phenanthroline , L= H, CO, Cl, TFA) — have been studied by combined Density Functional/Time-Dependent Density Functional (DFT/TDDFT) techniques using different combinations of DFT exchange-correlation functionals and basis sets. We demonstrate a correlation between HOMO-LUMO energy gap, Stokes shift, and T1 distortion, which reflects the effects of parent ligand and electron-withdrawing and donating groups. The results of this study of Ru-phen complexes revealed that this correlation is valid only when the metal-to-ligand charge-transfer (MLCT) transition is not isoenergetic with other transitions. In addition, we successfully developed new force field parameters for Ru-bpy based complexes, using molecular mechanics (MM) combined with molecular dynamics (MD), which can help to explain critical aspects of the optical phenomena of Ru-bpy based complex in solution and biological systems