A DITOPIC TETRADENTATE PYRIDYL AMINE LIGAND CONTAINING AN ANTHRACENE FRAGMENT - FLUORESCENCE INTENSITY AND CLOSED VS.OPEN SPECIES FORMATIONIN THE PRESENCE OF CU2+, AS A FUNCTION OF PH

The compounds 9,10-bis(2-pyridylmethylaminoethyl)anthracene L-1 and 9- (2-pyridylmethylaminomethyl)anthracene L-2, based on nitrogen donors o f the amine and pyridine type, were prepared and their properties exam ined in aqueous solution (water-1,4-dioxane 1:4 v/v). The protonation constants of both have been determined by means of potentiometric titr ations and the obtained species vs. pH distribution diagrams superimpo sed on the fluorescence intensity vs. pH profiles. This revealed an 'o ff-on-off' window behaviour: the fluorescence intensity is high only i n the pH range in which both free pyridine and protonated amines exist . Moreover, the formation constants of the complex species which form in the presence of 1 or 0.5 (in the case of L-1 and L-2, respectively) equivalent of Cu-II have been determined by means of potentiometric t itrations. In particular, in the case of the tetradentate ditopic liga nd L-1 the 'closed' two ligand-two metal species [Cu2L21](4+) and [Cu2 L21(OH)](3+) form in basic solution, in addition to two ligand-one met al partially protonated 'open' complex species. Moreover, a strong var iation of the fluorescence intensity of the anthracene fragment signal s the formation of the 'closed' species with respect to the 'open' one s, while a more subtle variation of the fluorescence intensity also al lows one to distinguish between [Cu2L21](4+) and [Cu2L21(OH)](3+).