Computational Investigation of the Ground States and Luminescent Excited States of Ruthenium(II) and Platinum(II) Photoactive Complexes: Insights into the Design of New Ruthenium(II)-Based Molecular Photocatalysts and Enhanced Understanding of Metal-Metal Bonded Exciplexes
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This study investigated the luminescent PtII complexes of Pt2(P2O5H2)44- (PtPOP), Pt2(P2O5H2)44- -Au(CN)2K (PtPOP-Au) and RuII complexes of Ru(bpy)3+ (bpy = 2,2’-bipyridine), and Ru(taz)32+ (taz = 3,3’-bis(5,6-dimethyl-1,2,4-triazine)) through density functional theory calculations using the Amsterdam Density Functional (ADF) program. It involved conducting an integrated study of the ground and first triplet excited states of each complex through geometric, charge, bond order, and spectroscopic analyses. These analyses help us to better understand the excited state charge transfer mechanism of the Ru(taz)3+ and excited state metal-metal bonding of PtPOP-Au (as compared to their respective well-characterized complexes of Ru(taz)3+ and PtPOP). Ru(taz)32+ exhibited metal-to-ligand charge transfer (MLCT) and PtPOP-Au exhibited metal-localized bonding (Pt-Pt bond formation from a dσ* to pσ transition) upon promotion to their first triplet excited states. While both absorption spectra had a similar dσ* to pσ peak, PtPOP-Au absorbed at lower energies than PtPOP. Pt-Pt bond distances of both PtPOP and PtPOP-Au shortened upon excitation. Yet, Au(CN)2K elongated the excited state Pt-Pt bond distance, demonstrating that PtPOP bonding character weakens in the presence of another metal ion. A preliminary comparison of other Pt-POP exciplexes showed that PtPOP-Au is similar to PtPOP-Ag and PtPOP-Tl in weakening Pt-Pt bonding character. Ru(taz)32+ is energetically similar to Ru(bpy)32+ and had broad absorption within the visible range, making it a viable photocatalyst. There were no significant changes in geometric structures upon excitation of the ruthenium complexes
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