Determination of Proton Dissociation Constants in the Excited State of Naphthylamines by Dynamic Analyses

A picosecond time-resolved study on prototropic reactions of electronically excited 1,5- and 1,8-diaminonaphthalenes in aqueous solution

“…The proton-dissociation rates thus obtained are 0.6 × 10 9 , 5.6 × 10 9 , and 1.3 × 10 10 s −1 for 1-AN, 1,5-DAN and 1,8-DAN, respectively. The k dis value obtained for 1-AN is somewhat smaller than the reported value (1.3 × 10 9 s −1 ), 14 and those for 1,5-DAN and 1,8-DAN are significantly larger than that of 1-AN. The substantial increase in the deprotonation rate of 1,5-DAN and 1,8-DAN can be attributed to the electronwithdrawing effect due to the ammonium group at the position 5 or 8 in the dication forms and is consistent with the prediction based on the PA values of the deprotonated forms.…”

“…For 1-aminonaphthalene (1-AN) steady-state and nanosecond time-resolved fluorescence measurements have been carried out. 14 The excited state proton-dissociation rate from its protonated form is reported to be 1.3 × 10 9 s −1 which is much slower than that of 1-naphthol (2.5 × 10 10 s −1 ) 15 in the excited state. Dogra et al 16,17 have reported the effects of ) and monoprotonated form (monocation: DANH + ) of 1,5-DAN and 1,8-DAN in the S 1 state (pK a *) have been evaluated by fluorimetric titrations to be −6.3 and −6.5, respectively.…”

Excited-state proton-dissociation of N-alkylated anilinium ions in aqueous solution studied by picosecond fluorescence measurements

“…Relatively small E a values ($10 kJ mol À1 ) are seen for AN and two monoalkylated ANs, and much larger E a values for dialkylated ones. Similar propensities have also been recognized 8 for protonated 1naphthylamine and N,N-dimethyl-1-naphthylamine, where the k dis values of these molecules were evaluated by dynamic analyses as 1.3 Â 10 9 s À1 for 1-naphthylamine and 9.6 Â 10 6 s À1 for N,N-dimethyl-1-naphthylamine.…”

“…The acidity of organic acids is usually enhanced remarkably upon photoexcitation because of differences in electronic structures between their ground and excited states. [1][2][3][4][5][6][7][8][9][10][11][12][13] The fluorescence spectra of such compounds often consist of two emission bands; the band at shorter wavelength corresponding to emission from the acid form and that at longer wavelength being ascribed to the conjugate base. Since the relative fluorescence intensities between these two bands depend strongly on the local environment in the vicinity of the substrate, these molecules are suitable for investigations of the local properties and structure of various organized molecular systems such as micelles and lipid bilayers, and the nature of biologically important protontransport phenomena.…”

“…[21][22][23] In the case of protonated aromatic amines, the influence of the geminate recombination on the proton-dissociation reactions in the excited state is expected to be negligible because of the absence of ion pair formation. We have determined the proton-dissociation rate constant and the excited-state acid dissociation constant (pK a *) for protonated 1-naphthylamine in H 2 O-CH 3 CN (95 : 5 v/v), 8 1-phenanthrylamine in H 2 O-CH 3 CN (9 : 1 v/v), 9 and 1-aminopyrene in H 2 O-CH 3 CN (1 : 1 v/v), 10 as 1.3 Â 10 9 s À1 (pK a * ¼ À1.0), 8.1 Â 10 8 s À1 (pK a * ¼ À0.76), and 1.8 Â 10 9 s À1 (pK a * ¼ À1.23), respectively, by nanosecond time-resolved spectroscopy with fluorimetry. We have suggested that the pK a * values of these amines cannot be determined directly from the Fo ¨rster cycle and fluorescence titration curve, and dynamic analyses by means of time-resolved fluorescence spectroscopy must be employed to determine the correct pK a * values.…”