Photosensitized Electron-Transfer Reactions in β-Cyclodextrin Aqueous Media: Effects on Dissociation of Ground-State Complexes, Charge Separation, and H2 Evolution

Eti Adar, Yinon Degani, Zafrir Goren, Itamar Willner*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

83 Scopus citations

Abstract

Zinc(II) meso-tetrakis[1-(3-sulfonatopropyl)-4-pyridino]porphyrin, ZnTPSPyP (2), forms a ground state complex with anthraquinone-2-sulfonate, AQS- (1). The formation of the complex results in internal static quenching of the excited S state of the sensitizer and recombination of the photoproducts in the cage structure. In the presence of β-cyclodextrin (β-CD), the complex is separated due to selective association of AQS- to the receptor cavity. This process leads to the effective decay of excited ZnTPSPyP to the T state that undergoes diffusional quenching by β-CD-bound AQS-. The electron-transfer photoproducts are stabilized against back-electron-transfer reaction and AQHS can be accumulated under continuous illumination in the presence of cysteine as the electron donor. Photoreduction of N,N’-dioctyl-4,4’-bipyridinium, C8V2+, with Ru(bpy)3 2+ as the sensitizer and Na2EDTA as the donor leads to the formation of a dimer aggregate (C8V)2. The aggregate is inactive in H2evolution. In the presence of β-CD, the aggregate formation is prevented due to the selective association of C8V monomer to the cyclodextrin cavity. High quantum yields for H2 evolution in the presence of a Pt-colloid are observed with β-CD, ϕ = 4 × 10–2. Flash photolysis studies reveal that the association of C8V to the β-CD stabilizes the intermediate photoproducts against back-electron-transfer reactions.

Original languageEnglish
Pages (from-to)4696-4700
Number of pages5
JournalJournal of the American Chemical Society
Volume108
Issue number16
DOIs
StatePublished - 1986

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