Azacrown Ethers with Naphthyl Branches. Fluorescence Properties, Protonation and Metal Coordination (original) (raw)

2007, Journal of Inorganic and Organometallic Polymers and Materials

Starting from 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane, we have prepared two compounds by replacing the amine hydrogens with naphthyl or 3,5-bis (2 0 -oxymethylnaphthyl)benzyl units. The absorption and emission spectra of compounds 2 (N,N 0 -bis(2-naphthylmethyl)-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane) and 3 (N,N 0 -bis[3,5-bis(2 0 -oxymethylnaphthyl)benzyl]-1,4,10, 13-tetraoxa-7,16-diazacyclooctadecane) have been studied in CH 3 CN:CH 2 Cl 2 1:1 (v/v) solution. For comparison purposes, the spectroscopic properties of N-methyl(2methylnaphthalene)ethylamine (1) have also been investigated. For each compound, the absorption spectra are qualitatively very similar to that of naphthalene, with molar absorption coefficients as expected for the presence of one (1), two (2), and four (3) naphthyl chromophoric groups. The fluorescence spectra, however, are quite different from that of naphthalene. The naphthalene-type fluorescence (k max = 337 nm) is strongly quenched, particularly for compounds 1 and 2 which also exhibit a broad emission band in the visible region (k max & 480 nm) assigned to a low lying charge-transfer excited state. In the case of compound 3, a quenched naphthalene-type band is accompanied by weak exciplex and excimer emissions. Upon titration with CF 3 SO 3 H, the charge transfer bands of 1 and 2 and the exciplex emission of 3 disappear and the naphthalene-type bands regain intensity. Titration plots show that in compounds 2 and 3 the protonation of the two nitrogens occurs stoichiometrically in two distinct steps. Titration with Zn 2+ gives rise to 2.Zn 2+ and 3.Zn 2+ complexes.