Excited-State Proton-Transfer Reactions of Naphthylammonium Ion-18-Crown-6 Complexes

Article abstract of DOI:10.1021/ja00299a035

Proton-transfer reactions in the excited singlet state of naphthylammonium ion-18-crown-6 complexes in MeOH-H2O (9:1) mixtures have been studied by means of the single photon counting method with fluorimetry.It is found that the complex formation of naphthylammonium ions with 18-crown-6 decreases markedly the proton-transfer rate (k₁) in the excited state, resulting in an increase of its lifetime.The back protonation rate in the excited state is negligibly small compared with those of the other decay processes; there is no excited-state prototropic equilibrium in the naphthylammonium ion-crown complexes (RN(1+)H3-crown).The one-way proton transfer reaction is elucidated by the presence of the excited neutral amine-crown complex (RNH2-crown)^* produced by deprotonation of (RN(1+)H3-crown)^*, where protonation to the amino group is structurally blocked by 18-crown-6 and the naphthyl group (R) of the complex.However, proton-induced quenching (k'_q) occurs effectively especially in the 1-naphthylammonium ion-crown complex.The ground-state association constants (K_g) of the complexes can be determined easily by the fluorescence titration method.Temperature effects upon the excited-state proton-transfer reactions of the complexes have been also carried out in order to study their thermodynamic properties.A Corey-Pauling-Kolton model of the anilinium ion-18-crown-6 complex proposed by Izatt et al. is strongly supported by the present work.