Selective fluorescent detection of Fe$$^{2+}$$ ions using 1-phenyl sulphonyl pyrrole and supramolecular modulation by $$\beta $$-cyclodextrin

This study presents a simple and selective fluorescent chemosensor for detecting $$ \text {Fe}^{2+} $$ ions in aqueous media using 1-phenyl sulphonyl pyrrole (PSP). To understand the effect of host–guest modulation, the sensing performance of PSP was investigated both in the free state and in the state where it was complexed with $$ \beta $$ -cyclodextrin ( $$ \beta $$ -CD). Spectroscopic studies show that upon addition of $$ \text {Fe}^{2+} $$ ions, PSP undergoes a significant increase in fluorescence, while the addition of other metal ions hardly affects the fluorescence, demonstrating high selectivity. 2D ROESY NMR spectroscopy was used to confirm the inclusion of PSP in $$ \beta $$ -CD and the binding stoichiometry of the PSP- $$ \beta $$ -CD complex was found to be $$ 1:1 $$ with an association constant of $$ 131.81 \, \text {M}^{-1} $$ . In contrast, the binding of $$ \text {Fe}^{2+} $$ to PSP was found to be $$ 1:1 $$ with a much higher constant of $$ 3450.83 \, \text {M}^{-1} $$ demonstrating strong chelation affinity. The detection limit for $$ \text {Fe}^{2+} $$ was found to be $$ 4.45 \times 10^{-7} \, \text {M} $$ . Inclusion of ß-CD reduces the $$ \text {Fe}^{2+} $$ binding ability and suppresses the $$ \text {Fe}^{2+} $$ -induced fluorescence response of PSP, demonstrating a controllable on–off sensing mechanism. The development of host-guest $$ \text {Fe}^{2+} $$ sensors for environmental and biological monitoring applications is demonstrated.