A styrylpyridinium dye as chromogenic and fluorogenic dual mode chemosensor for selective detection of mercuric ion: Application in bacterial cell imaging and molecular logic gate

Abstract

The present work demonstrates design, synthesis and chemosensing application of a styrylpyridinium based donor-π-acceptor (D-π-A) chromophore (L1) containing NS2O2 binding site. The chemosensor L1 selectively and successfully detects Hg2+ ions both visually and spectro-photometrically in perfect aqueous medium as well as in an aqueous-alcoholic mixture. Contrary to the reported literature on mercury sensing by cyanine dye which were reported to be “turn-off” Hg2+ sensor, probe L1 shows fluorescence “turn-on” response. D-π-A chromophore L1 exhibits orange colour in aqueous and aqueous-alcoholic solutions due to intramolecular charge transfer (ICT) from the N, N-disubstitutedaminostyryl donor to pyridinium acceptor moiety. It shows Hg2+-specific colour change with concomitant generation of a new absorption band and large emission enhancement (~10 fold) along with a blue shift of emission peak, owing to the formation of a selective 1: 1 L1-Hg2+ complex. 1H NMR analysis reveals the binding mode of L1 with Hg2+. Hg2+ probing process was found to be reversible in presence of sulphide anion. The reversible off-on-off fluorescence response of the sensor with Hg2+ and S2− has been used to generate an INHIBIT molecular logic gate. The probe not only provides a highly efficient, low cost, portable sensor for recognition and naked-eye detection of Hg2+ with a low detection limit in aqueous solution but its turn-on fluorescence response and cell permeability offer the possibility of using it for fluorescence imaging in living cells.