A highly sensitive fluorescence 'turn on' detection of perrhenate Anion, a non-radioactive surrogate of hazardous pertechnetate anion

Perrhenate oxoanion is a non-radioactive surrogate of the radioactive and hazardous pertechnetate oxoanion. The efficient sensor systems for perrhenate anion in aqueous medium is barely reported and still remains challenging due to low charge density and large size of the anion. In this regard, we have identified a cyanine based molecular rotor probe, pseudoisocyanine, which produces an appreciably larger emission enhancement of ∼60 fold in response to perrhenate anion, which is highest reported, till date, for any turn-on sensor for perrhenate anion leading to a significant improvement in the detection limit (0.17 μM) over existing sensors for perrhenate. Our sensing scheme operates through the ion pairing interaction between perrhenate and pseudoisocyanine which induces the formation of J-aggregates of pseudoisocyanine that yield dramatic changes in its fluorescence properties. The J-aggregate formation of pseudoisocyanine, in the presence of perrhenate anion, also yields significant changes in the absorption properties providing an opportunity of dual sensing of perrhenate, i.e. via fluorimetry and colorimetry. Apart from being sensitive and selective, our probe molecule exhibits a desirable feature of emission and excitation wavelength lying in the red region of the visible specrum which is advantageous for operation of a probe molecule in complex sensing matrix.