Soft matter pH sensing: from luminescent lanthanide pH switches in solution to sensing in hydrogels

The synthesis, complexation, and photophysical properties of the Eu(III)-based quinoline cyclen conjugate complex Eu1 and its permanent, noncovalent incorporation into hydrogels as sensitive, interference-free pH sensing materials for biological media are described. The Eu(III) emission in both solution and hydrogel media was switched reversibly on-off as a function of pH with a large, greater than order of magnitude enhancement in Eu(III) emission. The irreversible incorporation of Eu1 into water-permeable hydrogels was achieved using poly[methyl methacrylate-co-2-hydroxyethyl methacrylate]- based hydrogels, and the luminescent properties of the novel sensor materials, using confocal laser- scanning microscopy and steady state luminescence, were characterized and demonstrated to be retained with respect to solution behavior. Water uptake and dehydration behavior of the sensor-incorporated materials was also characterized and shown to be dependent on the material composition.

A modular approach to luminescent dinuclear ruthenium(II) and rhenium(I) complexes

A series of dinuclear (bipyridine)tricarbonylrhenium(I) and tris(bipyridine)ruthenium(II) complexes have been isolated and characterised, bridged by a flexible diamido ethylene glycol chain. A new stepwise synthetic pathway has been investigated to heterometallic complexes, with the rhenium(I) complexes exhibiting an unusual configuration and inequivalence of the metal centres potentially arising from a surprising hydrogen-bonding interaction between an Re–CO group and an amide proton in low-polarity solvents. This interaction appears to be broken by competing hydrogen-bonding species such as dihydrogen phosphate. This effect was not observed in the corresponding ruthenium(II) complexes, which showed very little interaction with anions. The photophysical characterisation shows that the inclusion of two ester/amide groups to the rhenium centre effectively quenches the fluorescence at room temperature. The ruthenium(II) complexes have considerably stronger fluorescence than the rhenium species, and are less affected by theinclusion of ester and amide groups to the 2,2'-bipyridine chelating group.