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THE PHOTOREDUCTION OF METHYLENE BLUE BY ARYLAMINOMETHANE‐SULFONATES
Author(s) -
NEUMANN MIGUEL G.,
MATTHEWS J. IOAN,
BRASLAVSKYdR SILVIA E.
Publication year - 1984
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1984.tb03400.x
Subject(s) - flash photolysis , chemistry , photochemistry , methylene , methylene blue , reaction rate constant , triplet state , quenching (fluorescence) , steric effects , electron transfer , fluorescence , medicinal chemistry , kinetics , stereochemistry , photocatalysis , organic chemistry , molecule , catalysis , physics , quantum mechanics
— The photoreduction of methylene blue in the presence of arylaminomethanesulfonates (RAMS = RC 6 H 4 NHCH 2 SO 3 Na) was studied by laser and conventional flash photolysis. These compounds quenched the methylene blue triplet deviating from a normal Stern‐Volmer behaviour. For low quencher concentrations, a Rehm‐Weller relationship was found between the k q 's and the DL G 's obtained for the electron transfer reactions. The lack of further quenching at higher [RAMS] is ascribed to the formation of a ground state ion pair between the dye and the anionic quencher which, on excitation, forms a triplet state unable to under go electron transfer for steric reasons. A second order decay rate constant was found for the semireduced species (MB') ( ca. 5 × 10 9 M ‐1 s ‐1 , independent of the RAMS used) and is attributed to a proton transfer from the radical zwitterion (RC 6 H 4 NH CH 2 SO 3 − ) to MB. The overall dependence on the substituent of the bleaching observed by continuous irradiation follows the triplet behaviour.