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

Abstract

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 Förster cycle) is proposed. Isotope effects on the rate constants and pK^*_a values have also been examined.