Reversible luminescent gels containing metal complexes

Gelators are the compounds capable to solidify various solvents and water. Organic gels and in particular the hydrogels are interesting soft materials with many potential applications. In this paper we report the formation of luminescent gels in water and in dimethylformamide as solvents. Gels were prepared by using the carboxylate-based aliphatic gelator 1 and the N, N’ -bis(O-methyl-TyrOH) oxalamide derivative 2. The gels are transparent and form fiber-like structures also in the presence of the red luminescent moiety, a Eu(III) hemicaged complex. The spectroscopic behaviour of the complex has been 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 into the gel network, a ruthenium complex, Ru(bpy)2(dppz)2+ (where bpy = 2, 2´bipyridine and dppz =dipyrido[3, 2-a:2´, 3´-c]phenazine) has also been employed. The complex is infact non-luminescent in water, while it is emitting when incorporated in the gel. Such “ switching on” behaviour is attributed to the incorporation of the complex into the lipophilic environment of gel fibers where it is shielded from quenching by water molecules.