Excited-State Electron Transfer in a Chromophore-Quencher Complex. Spectroscopic Identification of a Redox-Separated...

Area of Science:

• Photochemistry
• Coordination Chemistry
• Spectroscopy

Background:

• Ruthenium and rhenium polypyridyl complexes are widely studied for their photophysical properties.
• The incorporation of acceptor units into ligand frameworks can modulate excited-state properties.
• Dppz (dipyrido[3,2-a:2',3'-c]phenazine) derivatives offer versatile platforms for functionalization.

Purpose of the Study:

• To synthesize and characterize a novel rhenium complex, fac-[Re(Aqphen)(CO)3(py-PTZ)]+, featuring a quinone acceptor.
• To investigate the excited-state dynamics and electron transfer processes in this complex.
• To elucidate the nature of the long-lived transient observed upon photoexcitation.

Main Methods:

• Laser flash photolysis at 354.7 nm in 1,2-dichloroethane.
• Transient absorption spectroscopy.
• Time-resolved resonance Raman spectroscopy.
• Time-resolved infrared spectroscopy.

Main Results:

• The complex fac-[Re(Aqphen)(CO)3(py-PTZ)]+ exhibits a long-lived transient upon photoexcitation (tau = 300 ns at 298 K).
• Spectroscopic evidence confirms the transient is a redox-separated state: fac-[Re(I)(Aqphen(*)(-)())(CO)3(py-PTZ(*)(+)())]+.
• The excited electron is primarily localized on the quinone moiety of the Aqphen ligand.

Conclusions:

• The pendant quinone acceptor in the Aqphen ligand facilitates efficient intramolecular electron transfer upon photoexcitation.
• The rigid ligand framework and acceptor localization contribute to the stability of the observed redox-separated state.
• This study demonstrates a strategy for designing photoactive metal complexes with tunable electron transfer properties.