A sensitive and selective zinc ion ratiometric fluorescence sensor has been synthesized and characterized. This material displays dual fluorescence. After the material was bonded to a closed-shell metal ion, such as Zn2+, the recovery of the local excited fluorescence of the material-Zn2+ complex, largely at the expense of the intramolecular charge transfer fluorescence, is consistent with the difference between selected orbital transitions of the free dye and the metal-chelated complex. For instance, the contribution of the πtpy→πtpy* transition becomes more prominent. This is also consistent with the results of the fluorescence decay behavior, measured via a time-correlated single photon counting setup. In contrast, the corresponding open shell Ni2+-bound complex quenches both kinds of photoluminescence, due to spin-orbit coupling.
