1,14-Dibromo-3,6,9,12-tetraoxatetradecane

1-(2-tryptanthrinylaminoacetoxy)-14-(1-pyrenecarboxy)-3,6,9,12-tetraoxatetradecane (T2NH-P5P) was synthesized as a fluorescent chemosensor for metal ions. We investigated the metal-ion recognition of T2NH-P5P by separately adding Mg(2+), Ca(2+), Ba(2+), Fe(2+), Fe(3+), Co(2+), Ni(2+), Cu(2+), Ag(+), Zn(2+), Cd(2+), Hg(2+), Al(3+), and Pb(2+) in an acetonitrile solution. When using excitation at 325 nm, which corresponds to the absorption of the pyrene unit of T2NH-P5P, emission at 600 nm, from the 2-aminotryptanthrin unit, was observed, indicating that intramolecular fluorescence resonance energy transfer (FRET) occurs in T2NH-P5P (FRET-on). However, when Fe(2+), Fe(3+), Ni(2+), Cu(2+), Cd(2+), Hg(2+), and Al(3+) were added to an acetonitrile solution of T2NH-P5P, the behavior changed from FRET-on to FRET-off, which means that the fluorescence of 2-aminotryptanthrin was quenched, whereas that of the pyrene group was revived (FRET-off). Especially, this behavior was remarkable for Fe(2+), Fe(3+), Cu(2+), and Hg(2+).

1-(2-Tryptanthrinylaminoacetoxy)-14-(1-pyrenecarboxy)-3,6,9,12-tetraoxatetradecane (T2NH-P5P) was synthesized as a fluorescent chemosensor for Al3+. Excited at 325 nm, corresponding to absorption of the pyrene unit of T2NH-P5P, emission at 600 nm from the 2-aminotryptanthrin unit has been observed, indicating that intramolecular fluorescence resonance energy transfer (FRET) occurs in T2NH-P5P. However, when Al3+ is added to a solution of T2NH-P5P, the fluorescence of 2-aminotryptanthrin is quenched (FRET-off), whereas that of the pyrene group is revived. Such a FRET "on-off" behavior of T2NH-P5P is not observed for other metal cations (Ca2+, Ba2+, and Zn2+).