АННОТАЦИЯ
Spontaneous and photoinduced protonation of 4-(2-naphthyl)pyridine (1) in solutions and in complexes with β-cyclodextrin (β-CD) and 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) was studied using the absorption and fluorescence spectroscopies. The structures and stabilities of complexes of compound 1 and its quaternized derivative, 1-methyl-4-(2-naphthyl) pyridinium perchlorate (3), with β-CD and HP-β-CD were examined by 1H NMR titration (logK = 1.5-2.3). The molecule of naphthylpyridine 1 is always in the cyclodextrin cavity, regardless of the pH value of the solution. 2-Hydroxypropyl-β-cyclodextrin binds better the neutral form of compound 1 than does β-CD, while naphthylpyridinium salts exhibit nearly equal affinities to both cavitands. According to spectroscopic data, pK a (1) is 5.12 in water, which favors protonation of the N atom both in the ground and excited states; as a result, the fluorescence spectrum exhibits only the band of the protonated form with a lifetime of 15 ns. The addition of HP-β-CD to a solution of naphthylpyridine 1 results in the formation of inclusion complex 1@HP-β-CD, lowers pK a to 4.62, and gives rise to a fluorescence band of the nonprotonated form of compound 1 with a lifetime of 1.25 ns. Therefore, the presence of compound 1 in the HP-β-CD cavity precludes its protonation in the excited state. The initial portions of the fluorescence curves for compound 1 in solution and in its complex with HP-β-CD obtained upon pulsed excitation were compared to propose the initiation mechanism of short-lived fluorescence of the nonprotonated form of naphthylpyridine 1. Quantum chemical modeling of the protonation and complexation of compound 1 in the presence of water was performed. Based on the results obtained, a reversible photoinduced mechanical motion of naphthylpyridine 1 in the HP-β-CD cavity was suggested. © 2010 Springer Science+Business Media, Inc.
ЦИТАТА
Spectroscopic properties, structure, and photoinduced motion of 4-(2-naphthyl)pyridine in cyclodextrin cavities / V.B. Nazarov, T.G. Vershinnikova, V.Y. Gak, V.G. Avakyan, S.P. Gromov, A.I. Vedernikov, M.V. Fomina, N.A. Lobova, V.Y. Rudyak, M.V. Alfimov // Russian Chemical Bulletin. – 2010. – Т. 59. – № 5. – P. 941-953
