Fluorometric Detection of pH and Metal Cations by 1,4,7,10-Tetraazacyclododecane (Cyclen) Bearing Two Anthrylmethyl Groups

1,4,7,10-Tetraazacyclododecane (cyclen) bearing two anthrylmethyl groups (1,7-bis(9-anthrylmethyl)-1,4,7,10tetraazacyclododecane, L2) was synthesized and used as a fluorescent chemosensor for detection of pH and transition metal cations in aqueous solution. The fluorescent response and complexation properties of L2 were studied in comparison with those of a cyclen with a single anthrylmethyl group that was previously reported (1-(9-anthrylmethyl)-1,4,7,10tetraazacyclododecane, L1). Although L2 showed a less sharp response than L1, L2 demonstrated fluorescence behavior similar to that of L1, showing strong fluorescence at a low-pH region (pKa = 8.4) and in the presence of Zn2+ and Cd2+ but showing weak fluorescence at a high-pH region and in the presence of Cu2+. Chemical stability test by 1H NMR revealed that L2 is very stable even if left to stand under a humid atmosphere for 30 days, suggesting that L2 may be a potential effective fluorescent chemosensor for detection of pH and transition metal cations in aqueous solution.