Efficient charge separation in porphyrin-fullerene-ligand complexes

Area of Science:

• Photochemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Fullerene and porphyrin derivatives are key components in artificial photosynthesis and organic electronics.
• Understanding photoinduced electron transfer (ET) in their complexes is vital for designing efficient light-harvesting systems.

Purpose of the Study:

• To investigate the photophysical processes occurring upon complexation of a pyridine-functionalized C60 fullerene derivative with ruthenium- and zinc-tetraphenylporphyrins (tpp).
• To elucidate the role of solvent polarity in dictating the deactivation pathways of photoexcited porphyrins.

Main Methods:

• Time-resolved optical spectroscopy
• Transient Electron Paramagnetic Resonance (EPR) spectroscopy
• Study of complexes in various solvents (toluene, THF, benzonitrile)

Main Results:

• In toluene, triplet-triplet energy transfer deactivates photoexcited [Ru(tpp)].
• In polar solvents, electron transfer (ET) from porphyrin to fullerene is dominant.
• Complexation with [Zn(tpp)] is reversible, yielding efficient charge separation upon excitation.
• Radical-ion pairs (RPs) are formed via intramolecular and intermolecular ET in polar solvents.
• Charge-separated states exhibit lifetimes of ~10 microseconds in THF and several hundred microseconds in benzonitrile at room temperature.

Conclusions:

• Solvent polarity critically influences the photophysical pathways in fullerene-porphyrin complexes.
• Efficient charge separation and long-lived radical-ion pairs are achievable, particularly in polar solvents.
• These findings are significant for the development of advanced materials for solar energy conversion and molecular electronics.