A New Fluorescent Chemosensor for Cu2+ Based on a Dianthracene-Derivative

Abstract

Besides being of interest in photochemistry, photoinduced electron transfer (PET) is a process largely used in the design of fluorescent ion sensing molecules. One of the simplest systems is based on fluorescent aromatic groups linked to amino groups and proposed as possible fluorescent transition metal ion chemosensor 1]. In this case, the fluorescence of the fluorophore “ligths on” when the amino group is complexed. On the other hand, in the absence of metal ions, the fluorescence is quenched by a PET originating from the nitrogen lone electron pairs 2]. We prepared a new fluorescent chemosensor, abbreviated as Ant-NH-O-O-NH-Ant (shown in Fig. 1) in which the intramolecular PET is expected to be efficient. The chemosensor consists of a metal-binding dioxodiamino unit linked to two light-emitting anthracene fragments. This type of supramolecules when irradiated in methanol solution (conc. 1.89—10^?5 M.) at 368 nm displays a characteristic fluorescence spectrum for anthracene group with the most intensive band at 415 nm Fig. 2(a)]. The emission is slightly enhanced upon coordination of such metal ions as Ni²⁺ and Zn²⁺ by the ligand fragment of the Ant-NH-O-O-NH-Ant molecule Fig. 2(b) and (d)]. However, much higher intensity of emission is observed in the case of Cu²⁺ complex see Fig 2(c)]. The fluorescence enhancement is presumably due to suppression of photoinduced fluorophore-to-metal electron-transfer mechanism.