A photochromic dithienylethene, bearing a phenyl azacrown as an ionophore and a formyl group as an electron-accepting substituent, changes its binding ability for Ca2+ by a factor higher than 103 by photoirradiation. This new photoionochromic displays a wavelength-dependent competition between fluorescence and photocyclization assigned to a red-shifted absorption of the fluorescing conformer compared to the absorption of the photoreactive conformer.

Starting from the pentafluorophenyl ester of 4-(dimethylamino)benzoic acid, two dual fluorescent amide ligands with aza-15-crown-5 and 2-(aminomethyl)pyridine were obtained for sensing, respectively, alkali (alkaline-earth) and transition (heavy) metal cations. The crystal structure of the coppers II complex is reported. The Cu2+ is coordinated through the pyridine N- and amide O-atoms of two symmetry-related ligands. The azacrown-directed Ca-chelation to the N-atom of the amide leads to a slight quenching of the two fluorescence bands, In contrast, the pyridine directed Cull-chelation to the O-atom of the amide enhances the short-wavelength emission 17-fold over the locally excited state (LE), quenching the twisted intramolecular kcharge-transfer (TICT) emission. and, as a result, the intensity ratio I(LE)//(TICT) provides an accurate and sensitive measurement of the Cu-II concentration. These different cation effects are dependent on which atom (N vs. O) of the amide function participates in cation coordination: while the Ca2+ interaction with the N-atom electron pair leads to the deconjugation of the amide N-atom from the fluorophore, Cu2+ interaction with the lone pair of the O-atom of the carbonyl group increases the energy of the n-pi* but also of the L-1(a) transition and therefore close the channel to the TICT state.

Integrated supramolecular systems with a receptor built in a photo- or electroactive unit have been reviewed with the focus on their particular electronic properties and different photochemical and electrochemical processes which make them suitable for cation sensing or switching. The fluoroionophores with an electron donating ionophore have been the most investigated and their initial weakness related to cation decoordination in the excited state. The small blue-shift of the fluorescence spectrum and the slight change of the emission quantum yield upon cation complexation, have now been overcome by a careful combination of several donor and acceptor units, which provide new low-lying excited states decoupled from the complexed ionophore and by using TICT probes where the electronic coupling between the D and A parts is too small to induce decoordination of the cation during the excited state lifetime. On the contrary the switching action requires that the binding ability of the ionophore be lowered or increased on a larger time scale. This has been done by electrochemical oxidation and by insertion of the ionophore into a photochromic system. Differences in binding ability of three to four orders of magnitude have been obtained and it is our belief that integrated supramolecular systems combining an ionophore and a photochromic moiety (photoionochromics) will be for cation switching as successfull as integrated fluoroionophores have been for sensing cations.

New fluoroionophores, N-peralkylated dimers of aniline, are described.