Excited state pK*a values of naphthylamines: proton-induced fluorescence quenching

Tsutsumi, Kinzo; Shizuka, Haruo

doi:10.1016/0009-2614(77)80491-0

Cited by 68 publications

(31 citation statements)

References 8 publications

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“…This assumption is based on the fact that the other absorption bands are Gaussian. The value of k, thus obtained is 4 x lo8 dm3 mol-' s-' and is less than the value of k, generally observed for neutral amines (15,19). This is due to the positive charge already existed on the molecule.…”

Section: Efsect Of Solventscontrasting

confidence: 69%

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Unusual spectral shifts in the prototropic reactions of 2,7-diaminofluorene

Manoharan¹,

Dogra²

1987

Can. J. Chem.

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R. MANOHARAN and SNEH K. DOGRA. Can. J. Chem. 65, 2013Chem. 65, (1987. The red shift observed in the absorption spectrum of 2,7-diaminofluorene (DAF) in ether and acetonitrile is either due to the proton-donating capacity of the solute or due to its dispersive interactions with the solvent and a blue shift in methanol and water is due to the proton-accepting nature of DAF. DAF acts as a proton donor in S1 state in all solvents. The red shift in the fluorescence spectrum of the monocation of DAF relative to that of DAF is not because of the -NH2 group becoming more basic but because of the large solvent relaxating in aqueous medium. On the other hand, the monocation of DAF in cyclohexane follows the normal blue shift in the fluorescence spectrum. pK, values for the various prototropic reactions in So and SI states are determined and discussed.R. MANOHARAN et SNEH K. DOGRA. Can. J. Chem. 65, 2013Chem. 65, (1987. Lorsqu'on determine les spectres d'absorption du diamino-2,7 fluorkne (DAF) dans l'kther et dans l'acktonitrile, on observe un deplacement vers le rouge; ce resultat est dC1 soit a la capacite du solutC a donner des protons ou aux interactions dispersives du solvant. Par ailleurs, on observe un deplacement vers le bleu lorsque les spectres sont determines dans le mCthanol et dans l'eau; ces resultats sont dus a la nature du DAF qui a tendance a accepter des protons. Dans tous les solvants, le DAF agit comme donneur de proton dans 1'Ctat S, . Si on compare le spectre de fluorescence du monocation du DAF avec celui du DAF, on observe un dCplacement vers le rouge qui n'est pas dC1 au fait que le groupement -NH2 devient plus basique mais plutbt a la relaxation importante du solvant dans le milieu aqueux. Par ailleurs, le spectre de fluorescence du monocation du DAF dans le cyclohexane subit le dkplacement normal vers le bleu. On a determink et on discute des valeurs de pK, pour diverses reactions prototropiques dans les Ctats So et S,.[Traduit par la revue]During electronic transitions, the charge density changes at each atom of the molecule. Depending upon the nature of the transition as well as the nature of the molecule itself. the molecule may become less polar or more polar in the excited state as compared to the ground state. Due to this, the solvent molecules rearrange themselves in the S1 state, which is different from the ground state. Since the rearrangement of the solvent molecules involves bond breaking or bond formation, the time taken for this phenomenon can be compared with the period of vibrational motion and this is much smaller than the fluorescence lifetime. In other words, the fluorescence always occurs from the thermally equilibrated excited state even though the molecule, to begin with, is in the Franck-Condon state. The equilibrated state is of lower energy than the Franck-Condon state provided the polarity of the molecule changes (increases or decreases) and the solvent is polar (1, 2). Sometimes the stabilisation of the states, called solvent relaxation, is so large that either rev...

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Section: Efsect Of Solventscontrasting

confidence: 69%

“…The proton-induced fluorescence quenching mechanism can be compared with that proposed by Shizuka et al (19) monocation. k ,~ is calculated from Fig.…”

Section: Efsect Of Solventsmentioning

confidence: 98%

Unusual spectral shifts in the prototropic reactions of 2,7-diaminofluorene

Manoharan¹,

Dogra²

1987

Can. J. Chem.

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“…This lifetime is shorter than the one measured at pH 5.1 because aromatic amines undergo fluorescence quenching by protons under acidic conditions. 61,62 The estimated rate constant (k q ) for quenching the excited state Ph-A-Np by protons (Figure S2, SI) is between the k q values reported for neutral αand β-naphthyl amines. 62 The second shorter lifetime of less than 0.5 ns was assigned to the emission from protonated Ph-AH + -Np.…”

Section: ■ Results and Discussionmentioning

confidence: 73%

“…61,62 The estimated rate constant (k q ) for quenching the excited state Ph-A-Np by protons (Figure S2, SI) is between the k q values reported for neutral αand β-naphthyl amines. 62 The second shorter lifetime of less than 0.5 ns was assigned to the emission from protonated Ph-AH + -Np. These results are consistent with the fluorescence intensity of Ph-A-Np in water being higher than that of the protonated guest in the CB [7] complex.…”

Section: ■ Results and Discussionmentioning

confidence: 73%

Noninnocent Role of Na⁺ Ions in the Binding of the N-Phenyl-2-naphthylammonium Cation as a Ditopic Guest with Cucurbit[7]uril

2019

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Na + ions influence the mechanism for the binding of the ditopic guest N-phenyl-2-naphthylammonium cation (Ph-AH +-Np) to cucurbit[7]uril (CB[7]) by facilitating, at increased Na + concentrations, the formation of a higher order complex. Binding of the larger naphthyl moiety of Ph-AH +-Np forms the Ph-AH +-Np@CB[7] 1:1 complex (where "@" represents an inclusion complex) at low Na + ion concentrations (≤5 mM), whereas the inclusion of the smaller phenyl moiety in CB[7] (CB[7]@Ph-AH +-Np) is transient. Ph-AH +-Np@CB[7] is formed by reactions with free CB[7] and CB[7]•Na + (where "•" represents an exclusion complex) with displacement of the Na + cation. Because of the latter reaction, the dissociation of Ph-AH +-Np@CB[7] is faster at higher Na + concentrations. At high Na + concentrations (≥25 mM), the Na + ion stabilizes the inclusion of the phenyl moiety in CB[7] by capping the portal of CB[7]. The dynamics of the capped Na + •CB[7]@Ph-AH +-Np 1:1 complex is slower than in the absence of Na + capping. This stabilization of the phenyl moiety inclusion in CB[7] by Na + leads to the formation of the Na + •CB[7]@Ph-AH +-Np@CB[7] 2:1 host-guest complex, where each moiety of the ditopic guest is included in a different CB[7]. The opposing roles of Na + cations in the formation of the two 1:1 complexes are essential for the switch in mechanism with changes in Na + concentration and provide an example of systems chemistry, where new properties arise in the form of an increased diversity of complexes and altered complexation dynamics that depend on the system's composition.

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“…The ground-state equilibria between the cation−neutral (NH 3 + /NH 2 ) and neutral−anion (OH/O − ) were determined spectrophotometrically to be pK a1 = 4.4 ± 0.2 and pK a2 = 9.6 ± 0.2, respectively (see the SI), which are consistent with those reported for 8N2OH (pK a1 = 4.2 ± 0.2; pK a2 = 9.5 ± 0.2). 23 The similarity of these values to the pK a of the parent compounds, 2naphthylammonium (pK a = 3.9) and 2OH (pK a = 9.5), 41,47 suggests that the ground-state acidities of the two distal functional groups are independent of each other.…”

Section: ■ Results and Analysismentioning

confidence: 92%

Divergent Hammett Plots of the Ground- and Excited-State Proton Transfer Reactions of 7-Substituted-2-Naphthol Compounds

et al. 2019

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The rational design of photoacids requires accessible predictive models of the electronic effect of functional groups on chemical templates of interest. Here, the effect of substituents on the photoacidity and excited-state proton transfer (PT) pathways of prototype 2-naphthol (2OH) at the symmetric C7 position was investigated through photochemical and computational studies of 7-amino-2-naphthol (7N2OH) and 7-methoxy-2-naphthol (7OMe2OH). Time-resolved emission experiments of 7N2OH revealed that the presence of an electron-withdrawing versus electron-donating group (EWG vs EDG, NH3 + vs NH2) led to a drastic decline in photoacidity: pK a* = 1.1 ± 0.2 vs 9.6 ± 0.2. Time-dependent density functional theory calculations with explicit water molecules confirmed that the excited neutral state (x = NH2) is greatly stabilized by water, with equation-of-motion coupled cluster singles and doubles calculations supporting potential mixing between the La and Lb states. Similar suppression of photoacidity, however, was not observed for 7OMe2OH with EDG OCH3, pK a* = 2.7 ± 0.1. Hammett plots of the ground- and excited-state PT reactions of substituted 7-x-2OH compounds (x = CN, NH3 +, H, CH3, OCH3, OH, and NH2) vs Hammett parameters σp showed breaks in the linearity between the EDG and EWG regions: ρ ∼ 0 vs 1.14 and ρ* ∼ 0 vs 3.86. The divergent acidic behavior most likely arises from different mixing mechanisms of the lowest Lb state with the La and possible Bb states upon substitution of naphthalene in water.

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Excited state pK*a values of naphthylamines: proton-induced fluorescence quenching

Cited by 68 publications

References 8 publications

Unusual spectral shifts in the prototropic reactions of 2,7-diaminofluorene

Unusual spectral shifts in the prototropic reactions of 2,7-diaminofluorene

Noninnocent Role of Na⁺ Ions in the Binding of the N-Phenyl-2-naphthylammonium Cation as a Ditopic Guest with Cucurbit[7]uril

Divergent Hammett Plots of the Ground- and Excited-State Proton Transfer Reactions of 7-Substituted-2-Naphthol Compounds

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Excited state pK*a values of naphthylamines: proton-induced fluorescence quenching

Cited by 68 publications

References 8 publications

Unusual spectral shifts in the prototropic reactions of 2,7-diaminofluorene

Unusual spectral shifts in the prototropic reactions of 2,7-diaminofluorene

Noninnocent Role of Na+ Ions in the Binding of the N-Phenyl-2-naphthylammonium Cation as a Ditopic Guest with Cucurbit[7]uril

Divergent Hammett Plots of the Ground- and Excited-State Proton Transfer Reactions of 7-Substituted-2-Naphthol Compounds

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Noninnocent Role of Na⁺ Ions in the Binding of the N-Phenyl-2-naphthylammonium Cation as a Ditopic Guest with Cucurbit[7]uril