A FLUORESCENT CHEMOSENSOR FOR THE COPPER(II) ION

The two-component system anthracene-9-carboxylic acid 1,4,8,11-tetrath ia-cyclotetradecan-6-yl ester (1) has been synthesized, structurally c haracterized and investigated as a fluorescent chemosensor for the Cu- II ion. Crystallographic details for 1: space group P2,le with a=9.894 (2), b=24.608(2), c=10.759(2) Angstrom, alpha=90, beta=105.88, gamma=9 00; V=2519.7 Angstrom(3), Z=4 (R=0.088, R-W=0.066). In ethanolic solut ion 1 selectively incorporates Cu-II into its tetrathia crown componen t in the presence of other 3d metal ions and signals the recognition t hrough the quenching of the fluorescence of the anthracene fragment. Q uenching of the photo-excited state (which has a charge transfer natur e) takes place through a photo-induced electron transfer from the fluo rophore to the metal center and involves the Cu-II/Cu-I couple. The d( 10) cation Ag-I competes successfully with Cu-II for the tetrathia cav ity of 1 in an erhanolic solution (not in an acetonitrile solution),bu t the occurrence of the metal/receptor interaction cannot be signalled , due to the poor redox activity of the non-transition cation Ag-I.