Pyrazine-Functionalized Ru(II)-Complexes as Visible-Light Activated Photobases.

Area of Science:

• Photochemistry
• Coordination Chemistry
• Physical Chemistry

Background:

• Excited-state proton transfer (ESPT) significantly alters acid/base properties (up to 10 pK_a units) upon photoexcitation.
• Organic photobases have limitations like single use or UV absorption dependence.
• Metal complex-based photobases offer advantages, including visible light activation and reversible processes.

Purpose of the Study:

• To synthesize novel Ruthenium(II)-complexes with pyrazine-functionalized polypyridyl ligands.
• To investigate the photobasic properties and ESPT mechanisms of these complexes.
• To explore the potential of metal complexes for reversible photobase generation.

Main Methods:

• Synthesis of two novel Ruthenium(II)-complexes.
• Ultrafast spectroscopy to study excited-state proton transfer dynamics.
• Theoretical calculations to complement experimental findings.

Main Results:

• Metal-to-ligand charge transfer (MLCT) excitation in aqueous solution induced a ΔpK_a of 9 units.
• The ESPT process was observed to occur within approximately 300 picoseconds.
• Ruthenium complexes demonstrated efficient and reversible photobasic properties.

Conclusions:

• Novel Ruthenium(II)-complexes are effective visible-light-activated photobases.
• These complexes facilitate rapid and reversible excited-state proton transfer.
• Metal complex-based photobases present a promising alternative to organic counterparts.