Cyclic transmembrane charge transport mediated by low-potential pyrylium ions

Area of Science:

• Photochemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Earlier studies showed trimethy- and triphenyl-substituted analogues facilitated photosensitized transmembrane redox via electroneutral antiport.
• N-dialkylaminophenyl-substituted pyrylium and thiopyrylium ions absorb broadly across the visible spectrum.

Purpose of the Study:

• To investigate N-dialkylaminophenyl-substituted pyrylium and thiopyrylium ions as photosensitizers and redox mediators across bilayer membranes.
• To assess their potential for solar photoconversion and minimal photochemical systems.

Main Methods:

• Cyclic electron transport studies in transversely organized vesicles with phase-separated electron donors and Co(bpy)(3)(3+).
• Investigation of transmembrane diffusion independence from membrane microviscosity.
• Evaluation of combined photosensitizer/redox relay capabilities via direct oxidation of solvent or buffer ions from triplet-excited states.
• Redox titrations to determine radical reduction potentials.

Main Results:

• The investigated ions facilitated cyclic electron transport, with quantum yields independent of membrane microviscosity.
• Triphenylpyrylium and triphenylthiopyrylium ions acted as combined photosensitizers/redox relays, enabling minimal photochemical transmembrane charge separation.
• Low-potential visible-absorbing pyrylium ions were limited by thermodynamics but their radicals could reduce H+ to H2.
• These dyes effectively formed methyl viologen radical in photoinitiated transmembrane redox reactions.

Conclusions:

• N-dialkylaminophenyl-substituted pyrylium and thiopyrylium ions are effective photosensitizers and redox mediators for transmembrane charge separation.
• These visible-absorbing dyes hold promise for solar energy conversion applications.
• The demonstrated minimal photochemical schemes offer new pathways for artificial photosynthesis.