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[摘要]：1,4-Dioxa-7,13-dithia-10-azacyclopentadecane (AT(2)15C5) or 1,4,7,10-tetraoxa-13-azacyclopentadecane (A15C5) were attached as metal-ion-binding receptor units at the ortho or para positions of the 9-amino-N-phenylbenzo[b]quinolizinium chromophore. The addition of Hg(2+) or Mg(2+) to the para isomers of the AT(2)15C5-quinolizinium or A15C5-quinolizinium conjugate, respectively, led to a blueshift of the absorption maxima of each compound because of the reduced donor ability of the complexed amino group. In contrast, the addition of Hg(2+) to a solution of the ortho-AT(2)15C5-quinolizinium conjugate in H(2)O/MeOH mixtures induced a significant redshift (ca. 50 nm) of the absorption maximum and enabled the photometric discrimination between Hg(2+) and competing thiophilic cations, such as Ag(+) or Pb(2+), because the latter, as well as other competing metal ions, did not induce such an effect. It is proposed that the Hg(2+)-induced redshift originates from the complexation of Hg(2+) by the thiaazacrown ether followed by deprotonation of the secondary 9-amino substituent of the aminobenzoquinolizinium unit. The resulting amide functionality increases the donor-acceptor interplay leading to the redshifted absorption and also coordinates to Hg(2+) to form a lariat ether type complex. A similar effect was observed upon the addition of Mg(2+) to the 9-amino-N-phenylbenzo[b]quinolizinium derivative with the A15C5 unit in the ortho position; however, this effect was only operative in aprotic solvents, e. g. CH(3)CN, and with less than 1 mol-equiv. of Mg(2+). |
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