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Photoinduced Electron Transfer Reactions as Photosynthetic Models: Reduction of Anthraquinones in SiO 2 and ZrO 2 Colloids
Author(s) -
Willner Itamar,
Degani Yi
Publication year - 1982
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.198200031
Subject(s) - chemistry , photochemistry , electron transfer , photoinduced electron transfer , anthraquinone , electron acceptor , colloid , triethanolamine , semiquinone , redox , acceptor , aqueous solution , quinone , inorganic chemistry , organic chemistry , analytical chemistry (journal) , physics , condensed matter physics
Abstract The photoinduced reduction of anthraquinone‐2‐sulfonate, AQS − , and anthraquinone‐2,6‐disulfonate AQS 2‐ 2 , in a negatively charged SiO 2 colloid has been examined. Ru(bipy) 2+ 3 was used as sensitizer and triethanolamine, TEOA, as an ultimate electron donor. The reduction of the quinones to the corresponding semiquinone radicals, AQS 2‐ and AQS 3‐ 2 proceeds only with propylviologen sulfonate, PVS 0 , ( 1 ), as a mediating electron acceptor. The primary electron acceptor, PVS 0 , functions as an efficient quencher of the excited species. The formation of AQS 3‐ 2 is 4‐fold enhanced as compared to that of AQS 2‐ . This enhancement is attributed to the additional stabilization of AQS 3‐ 2 from recombination with the oxidized species, Ru(bipy) 3+ 3 , due to electrostatic repulsions from the colloidal interface. Consequently, the subsequent oxidation of TEOA is facilitated. Similarly, a positively charged ZrO 2 colloid has been used in controlling photosensitized electron transfer reactions. Anthraquinone‐2,6‐disulfonate, AQS 2‐ 2 , is photoreduced in the ZrO 2 colloid to the respective AQHS 2‐ 2 with the neutral sensitizer, Ru(bipy) 2 (CN) 0 2 , and cysteine as electron donor (Φ = 3 × 10 −2 ). No photoreduction of the quinone is observed in a homogeneous aqueous phase. The success in driving the photoinduced reaction in the ZrO 2 colloid is again attributed to the stabilization of the intermediate photoproducts from recombination by means of electrostatic interactions with the charged interface.