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IONIC STRENGTH EFFECTS ON THE GROUND STATE COMPLEXATION and TRIPLET STATE ELECTRON TRANSFER REACTION BETWEEN ROSE BENGAL and METHYL VIOLOGEN
Author(s) -
Douglas P.,
Waechter G.,
Mills A.
Publication year - 1990
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.1751-1097.1990.tb01788.x
Subject(s) - rose bengal , ionic strength , chemistry , reaction rate constant , ionic bonding , viologen , eosin , triplet state , quenching (fluorescence) , electron transfer , equilibrium constant , analytical chemistry (journal) , photochemistry , ion , inorganic chemistry , fluorescence , kinetics , molecule , aqueous solution , chromatography , organic chemistry , pathology , medicine , staining , physics , quantum mechanics
— The equilibrium constants, K c , for complexation between methyl viologen dication (MV 2 +) and Rose Bengal, or Eosin Y, decrease with increasing ionic strength. At zero ionic strength K c is 6500 (± 500) mol −1 dm 3 for Rose Bengal and 3200 (± 200) mol −1 dm 3 for Eosin Y, and these values decrease to 1500 (± 100) and 680 (± 40) mol −1 dm 3 , respectively, at an ionic strength of 0.1 mol dm −3 . K c is independent of pH between 4.5 and 10. Δ H is ‐25 (± 1) kJ mol −1 for complexation with either dye, whereas Δ S is ‐15 (± 3) J K −1 mol −1 for Rose Bengal, and ‐ 23 (± 3) J K −1 mol −1 for Eosin Y. The complexation constant for Rose Bengal and the neutral viologen, 4,4'‐bipyridinium‐ N, N' ‐di(propylsulphonate), (4,4'‐BPS), is 420 (± 35) mol −1 dm 3 , and independent of ionic strength. No complexation could be observed for either Rose Bengal or Eosin with another neutral viologen, 2,2'‐bipyridinium‐ N,N' ‐di(propylsulphonate), (2,2'‐BPS). MV 2 + quenches the triplet state of Rose Bengal with a rate constant of 7 × 10 9 mol −1 dm 3 s −1 , and this rate constant decreases slightly as ionic strength increases. The cage escape yield following quenching, Φ cc is very low (Φ cc = 0.02 (± 0.005), and independent of ionic strength. 4,4'‐BPS quenches the triplet state of Rose Bengal with a rate constant of 2.2 (± 0.1) × 10 9 mol −1 dm 3 s −1 , and gives a cage escape yield of 0.033 (± 0.006). 2,2'‐BPS quenches the Rose Bengal triplet with a rate constant of 6 (± 1) × 10 8 mol −1 dm 3 s −1 and gives a cage escape yield of 0.07 (± 0.01). Conductivity measurements indicate that MV 2 +(Cl − ) 2 is completely dissociated at concentrations below 2 × 10 −2 mol dm −3 .