Kinzo Tsutsumi

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

Abstract The dynamic bahavior of the excited singlet of naphthylamines involving proton-induced quenching in a sulfulic acid-water mixture has been studied by means of fluorometry and nanosecond time resolved spectroscopy. A significant fluorescence quenching of neutral α- and β-naphthylamines induced by protons was observed: 1 k q = 8.9 (±0.3) × 10 9 M −1 s −1 and 1 k q = 3.3 (±0.2) × 10 8 M −1 s −1 at 300 K, respectively. On the basis of kinetic analyses, the corrected values of pK * a were determined to be −1.0 (±0.2) and −0.8 (±0.1) for α- and β-amines, respectively. The isotope effect on the quenching was also examined.

Direct measurement of proton dissociation in thhe excited state of protonated 1-aminopyrene with picosecond pulses

Abstract Direct measurement of proton dissociation in the excited singlet state of protonated I-aminopyrene in a mixture of H 2 O (or D 2 O) and acetonitrile (1:1) has been carried out by means of picosecond time-resolved spectroscopy. The proton dissociation retes k 1 1 and k D+ 1 at about 300 K were determined tobe 3.7 (±0.6) * 10 9 s -1 , respectively. These rates are in very good agreement with those obtained by nanosecond time-resolved spectroscopy with fluorometry. The excited singlet state ;K * 2 value of l-aminopyrene was also determined by dynamic analyses.

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

The dynamic behavior of the excited singlet of naphthylamines in a sulfuric acid-water mixture has been studied by means of fluorometry and nanosecond time-resolved spectroscopy. It was found that a significant proton-induced fluorescence quenching is present in the neutral excited amines A* and the quenching is caused by an interaction between A* and H + other than protonation on the nitrogen atom of A*. The proton dissociation constants pK* of the excited singlet states of naphthylamines were determined by dynamic analyses. Isotope effects on the proton dissociation, association, and the quenching were examined.

Proton transfer reactions in the excited state of 1-aminopyrene by picosecond/streak camera and nanosecond spectroscopy

Abstract Proton transfer reactions in the excited singlet state of 1-aminopyrene in the presence of protons in H 2 O (or D 2 O)-acetonitrile mixtures (1 : 1) have been studied by means of picosecond/streak camera and nanosecond time-resolved spectroscopy with fluorimetry. Direct measurements of proton dissociation rates k 1 H+ and k 1 D− at 295 K were determined to be 1.8(±0.4) × 10 9 s −1 and 1.2(±0.3) × 10 9 s −1 , respectively. These rates agree with those obtained by nanosecond time-resolved spectroscopy. It is confirmed that dynamic analyses involving proton-induced quenching are needed to obtain the correct pK α * values of 1-aminopyrene.

Proton-transfer reactions in the excited state of phenanthrylamines by nanosecond spectroscopy and fluorimetry

Proton-transfer reactions in the excited singlet state of phenanthrylamines at 300 K have been studied by means of nanosecond time-resolved spectroscopy and fluorimetry. On the basis of dynamic analyses involving proton-induced fluorescence quenching, the proton dissociation (k1) and association (k2) rate constants and the acidity constants pK*a in the excited singlet state of phenanthrylamines were determined. The pK*a values are discussed theoretically by taking account of their electronic structures. An empirical equation to estimate approximately the correct pK*a values of aromatic amines using data from Stokes shifts and (pK*a)FC values (determined by the Forster cycle) is proposed. Isotope effects on the rate constants and pK*a values have also been examined.