A simple rhodamine-based dual signalling reversible molecular switch for recognition of Al(III) with Promising applications for advanced logic operations – ‘OR’, ‘Keypad Lock’ & ‘INHIBIT’ logic function and cell-imaging studies†.
A simple salicylaldimine-based receptor equipped with rhodamine moiety (L3) has been designed and synthesized for detection of Al3+ ions, which exhibits high sensitivity over other metal ions in aqueous buffer-methanol solution at physiological pH. It displays quick responses through visible colorimetric as well as fluorogenic changes on 1:1 binding to Al3+, as delineated by absorption and fluorescence titrations and also by Job’s method and ESI-MS+ studies. However, it exhibits calorimetric but not fluorometric responses towards Cu2+ and hence limits its colorimetric application towards the detection of Al3+ in the presence of Cu2+ ions. The properties of the probe like (i) solubility in aqueous buffer-methanol, (ii) cell-permeability and (iii) non-toxic nature towards cell may provide an opportunity for the in vitro/ in vivo bio study. The detection limit of Al3+ calculated by the 3σ method was found to be 24.8 pM. It is also found to be useful in the construction of logic gates; namely ‘OR’ gate (from absorption) and molecular ‘keypad lock’ (from emission) by the two chemical inputs (Al3+ and Cu2+) in the proper sequence of addition. The keypad lock operation is particularly important, as the output of the system depends not only on the proper combination but also on the order of input signals, creating the correct password that can be used to ‘‘open’’ this molecular keypad lock through strong fluorescence emission at 552 nm. Besides, “OFF–ON–OFF” fluorescence behavior observed in the presence of Al3+ and EDTA strengthens the potential applications of the L3–Al3+ system as a device with ‘INHIBIT’ logic gate functions. As a whole, its various logic gate properties may improve its impact for the development of new-generation ‘intelligence’ digital devices. To the best of our knowledge, this is the first report on the fluorescence emission of a rhodamine derivative induced by Al3+ binding with such multiple logic gate operations accompanied by its application to cell-biology.