New cyclometallated Ru(II) complex for potential application in photochemotherapy?

Area of Science:

• Inorganic Chemistry
• Photochemistry
• Materials Science

Background:

• Ruthenium complexes are investigated for photochemotherapy (PCT).
• Ligand exchange in related complexes ([Ru(biq)2(bpy)](PF6)2 and [Ru(biq)2(phen)](PF6)2) occurs upon red light irradiation in coordinating solvents.
• This ligand dissociation is attributed to steric hindrance from biquinoline (biq) ligands.

Purpose of the Study:

• To synthesize and characterize a novel cyclometallated ruthenium complex, [Ru(biq)2(phpy)](PF6) (1), for enhanced photochemotherapy (PCT) applications.
• To compare the photophysical properties and photochemical behavior of complex 1 with known photoactive complexes ([Ru(biq)2(bpy)](PF6)2 (2) and [Ru(biq)2(phen)](PF6)2 (3)).
• To understand the factors influencing photochemistry, specifically the lack of photoinduced ligand exchange in complex 1.

Main Methods:

• Synthesis and characterization of the cyclometallated complex [Ru(biq)2(phpy)](PF6) (1).
• Photochemical studies comparing complex 1 with complexes 2 and 3 under red light irradiation in coordinating solvents.
• UV-Vis spectroscopy to determine MLCT absorption maxima.
• Density Functional Theory (DFT) calculations to investigate electronic structure and orbital stabilization.

Main Results:

• Complex 1 exhibits a red shift in its MLCT absorption maximum by approximately 100 nm compared to complexes 2 and 3.
• Despite a distorted octahedral geometry, complex 1 does not undergo photoinduced ligand exchange.
• Complexes 2 and 3 exhibit ligand exchange, with complex 2 showing a ~2-fold greater quantum yield than complex 3.
• DFT calculations indicate that cyclometallation in complex 1 destabilizes the eg(σ*) orbitals, explaining the lack of photochemistry.

Conclusions:

• The cyclometallated complex [Ru(biq)2(phpy)](PF6) (1) shows potential for PCT due to its altered photophysical properties and resistance to photoinduced ligand exchange.
• The absence of ligand dissociation in complex 1, attributed to electronic effects from cyclometallation, distinguishes it from related photoactive ruthenium complexes.
• This study provides insights into the design of ruthenium complexes with tailored photochemical behavior for therapeutic applications.