2-Aminotryptanthrin Derivative with Pyrene as a FRET-based Fluorescent Chemosensor for Metal Ions

Abstract

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 Mg²⁺, Ca²⁺, Ba²⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Ag⁺, Zn²⁺, Cd²⁺, Hg²⁺, Al³⁺, and Pb²⁺ 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 Fe²⁺, Fe³⁺, Ni²⁺, Cu²⁺, Cd²⁺, Hg²⁺, and Al³⁺ 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 Fe²⁺, Fe³⁺, Cu²⁺, and Hg²⁺. T2NH-P5P is suitable for use as a fluorescent chemosensor for Fe²⁺, Fe³⁺, Cu²⁺, and Hg²⁺.