Quantum Mechanical Modeling and Molecular Dynamic Simulation of Ruthenium (Ru) Polypyridyl Complexes to Study Feasibility of Artificial Photosynthesis

A photochemical reaction is initiated by a charge separation process in the reaction center (RC) complex. Major research in this regard is to analyze the light driven electron transfer and to study the response of the molecule in which the RC is embedded, stabilizing the charge separation process in photosynthesis. In research related to artificial photosynthesis, modeling and simulation of highly energetic photosensitizers have been always a choice. Ruthenium (II) polypyridyl complexes are widely used in this regard. In this work these complexes have been successfully designed in the computational manner with a quantum mechanical model in the density functional level of theory (DFT) based on the local density approximation energy expression augmented by BLYP corrections using the DND basis set with 'all electron core' treatment option. In the analysis, band energy, electronic population, vibrational frequency, thermodynamic functions and energies of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) have been used. Molecular dynamic simulation studies were conducted to characterize the dynamic properties. In the analysis, the 'metal ligand charge transfer transition' (MLCT) in these complexes has been studied in detail. Thermodynamic stability of these complexes has been compared. The pi-electron acceptor properties of the tetra cyano ruthenium poly pyridyl complexes has been found to be in the order of bpz (2,2'-bipyrazine)> bptz (3,6-bis-(2-pyridyl)-1,2,4,5-tetrazine) > dpp (2,3-bis(2'-pyridyl) pyrazine) > bpy (2,2'-pyridine). The possibility for these compounds to be used as photosynthetic targets will also follow the same order.