2-Aminotryptanthrin derivative with pyrene as a FRET-based fluorescent chemosensor for Al3+.

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+).