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Onoue, Yoshiaki; Hiraki, Kei; Morishige, Kiyotoshi; Nishikawa, Yasuharu

doi:10.1246/nikkashi.1978.1237

Cited by 11 publications

(7 citation statements)

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“…15 Consequently, they convert to their deprotonated forms as soon as they are excited in aqueous solutions in the pH range 0-14. This photoacidity of the -OH moiety was first reported from 1959 to 1978 11,[16][17][18][19][20][21][22] for the N-protonated forms of the hydroxyquinolines (i.e., R ) H). The photoinduced proton ejection was further investigated by one of us in 1994 by combining time-resolved measurements with spectral studies in the case of 6-hydroxyquinoline.…”

Section: Introductionmentioning

confidence: 84%

Photoinduced Coupled Proton and Electron Transfers. 2. 7-Hydroxyquinolinium Ion

et al. 1999

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The hydroxyl group of 7-hydroxyquinoline in acidic media (i.e., of 7-hydroxyquinolinium cation, 7-HQ(C)) undergoes photoinduced deprotonation even in strongly acidic media. It occurs from dilute perchloric acid solutions up to 8 mol L -1 concentration, which is evidence of an outstanding photoacidity. Excited-state proton ejection was shown to be reversible at acid concentrations greater than 1 mol L -1 . Below this value, the proton ejection was not balanced by the proton recombination. Concerning the rates of the excited-state reactions, (i) the proton ejection rate constants k 1 increased upon acid dilution, attaining at high dilution the limiting value of (k 1 ) 0 ) 5.5 × 10 10 s -1 . k 1 was shown to vary with the water activity according to k 1 ) (k 1 ) 0 (a H 2 O ) 4 . The number 4 is then a key number for the ability of water to accept a proton from 7-HQ(C*). (ii) The proton recombination rate constant varies from 3 × 10 9 to 4 × 10 10 s -1 when the acid concentration ranges from 1 to 5 mol L -1 . This observation can tentatively be ascribed to a nondiffusional recombination process occurring with the ejected proton in concentrated acid solutions. The results as a whole are consistent with the coupling of an intramolecular electron transfer with the proton transfer, due to the withdrawing effect of the quinolinium function gNH + on the -O -group generated by the deprotonation. The photoproduct is then most likely to be the ketonic tautomeric form of 7-hydroxyquinoline rather than a zwitterion. Thus, the excited-state behavior is fully accounted for by the photoinduced synergy of the two functional groups.

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Section: Introductionmentioning

confidence: 84%

Photoinduced Coupled Proton and Electron Transfers. 2. 7-Hydroxyquinolinium Ion

et al. 1999

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“…In order to discuss the coordination ability of the metal ions with SNO, one of the well-known ligands, 8-hydroxyquinoline (8-HQ), was used for investigation of the metal chelation in ethanol solutions. [36][37][38][39] 8-HQ forms the metal complex, Q − -M n+ , in the ethanol solutions as follows:…”

Section: Chelation Of 8-hq With Metal Ionsmentioning

confidence: 99%

“…They were compared with that of a typical ligand, 8-hydroxyquinoline (8-HQ), in ethanol and silica gels because the metal ions can be coordinated to the nitrogen and oxygen atoms of MC as well as 8-HQ. [36][37][38][39] Scheme 2 illustrates the metal chelation of 8-HQ.…”

Section: Introductionmentioning

confidence: 99%

Chelation ability of spironaphthoxazine with metal ions in silica gel

Nishikiori

Teshima

Fujii

2012

Photochem Photobiol Sci

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“…Such acidities can be obtained only with concentrated sulfuric acid. However, sulfonation occurs and leads to a sulfo derivative whose fluorescence properties are different from those of the parent hydroxyquinoline. ,, That may be the reason why the only two published values of the quantum yield of 8-HQ(C*) in sulfuric acid available are quite different: 0.31 in 98% H 2 SO 4 , or 0.565 in 97% H 2 SO 4 …”

Section: Properties Of 8-hq In Aqueous Solutionsmentioning

confidence: 99%

“…38,40,41 That may be the reason why the only two published values of the quantum yield of 8-HQ-(C*) in sulfuric acid available are quite different: 0.31 in 98% H 2 SO 4 , 37 or 0.565 in 97% H 2 SO 4 . 42 The interpretation of the observed phenomena and especially of the fluorescence quenching in the major part of the acidity and pH range must take the nature of the excited form into account. Two cases are to be considered: the excited form is either the cationic 8-HQ(C) or the anionic 8-HQ(A) form, or on the contrary, it is the neutral form 8-HQ(N) (the pH ranges for the predominance of each form can be inferred from the above pK a values).…”

Section: Properties Of 8-hq In Aqueous Solutionsmentioning

confidence: 99%

Excited-State Processes in 8-Hydroxyquinoline: Photoinduced Tautomerization and Solvation Effects

et al. 1997

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8-Hydroxyquinoline (8-HQ), referred as to oxine in analytical chemistry, is a fluorogenic ligand. Its lack of fluorescence in water and alkanes, and its low quantum yield in many other organic solvents, are rationalized in the present study in terms of photoinduced formation of a nonfluorescent tautomeric form 8-HQ(T*). In water, intermolecular proton transfers with surrounding water molecules are expected, but intrinsic intramolecular proton transfer between the −OH and ⩾N functions cannot be ruled out because the presence of a weak internal H bond can be inferred from the ground-state properties of 8-HQ such as pK a values or solubility. In organic solvents, vapor pressure osmometry measurements in conjunction with infrared spectra allow us to show that (i) in alkane solvents, a very stable dimer is formed in the ground state (K dim = 7 × 107 at 25 °C); biprotonic concerted proton transfers are then expected to occur within the dimer upon excitation, as was previously reported for 7-azaindole; (ii) in chlorinated solvents (CH2Cl2, CHCl3), hydration by residual water molecules likely leads to a nonnegligible fraction of hydrated open structures where excited-state proton transfer is impaired; a weak fluorescence can then be observed (ΦF ≈ 4 × 10-3).

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Cited by 11 publications

References 0 publications

Photoinduced Coupled Proton and Electron Transfers. 2. 7-Hydroxyquinolinium Ion

Photoinduced Coupled Proton and Electron Transfers. 2. 7-Hydroxyquinolinium Ion

Chelation ability of spironaphthoxazine with metal ions in silica gel

Excited-State Processes in 8-Hydroxyquinoline: Photoinduced Tautomerization and Solvation Effects

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