Reversible luminescent gels containing metal complexes

Gelators are compounds capable of solidifying various solvents and water. Organic gels, and in particular hydrogels, are interesting soft materials with many potential applications. In this paper the formation of luminescent gels in water and dimethyl-formamide as solvents is reported. The gels are prepared by using a carboxylate-based aliphatic gelator (1) and a N,N'-bis(O-methyl-TyrOH) oxalamide derivative (2). The gels are transparent, and form fiberlike structures in the presence of the red luminsecent moiety, a Eu-III hemicaged complex. The spectroscopic behavior of the complex is investigated in different solvents and when is entrapped in the gel. In order to probe the involvement of the chemical structure of the luminescent moiety in the gel network, a ruthenium complex, Ru(bpy)(2)(dppz)(2+) (where bpy = 2,2'-bipryridine and dppz = dipyrido[3,2-a:2',3'-c]phenazine) has also been employed. The complex is in fact nonluminescent in water, while emitting when incorporated in the gel. Such "switching on" behavior is attributed to the incorporation of the complex into the lipophilic environment of gel fibers, where it is shielded from quenching by water molecules.