Aggregation induced emission active pyrene scaffold for real-time chromogenic and fluorogenic selective detection of...

A fluorogenic and chromogenic probe (L₁) bearing pyrenyl and naphthyl group was synthesized using 4-(naphthalen-1-yl) thiosemicarbazide and pyrene-1-carboxaldehyde. Sensor (L₁) exhibited significant Aggregation Induce Emission (AIE) property in 7:3 water-EtOH mixture and the aggregate exhibited a yellowish-green fluorescence upon excitation with 380 nm light. Upon adding Pd²⁺ ion, colourless EtOH/aqueous HEPES buffer (3:7, v/v) solution of L₁ showed a sharp change to bright yellow as well as fluorescence turn off response. Probe displayed high selectivity, sensitivity, rapid response time (50 s) and good pH tolerance range (5-8). Sensing was reversed in presence of triphenylphosphine. The detection limit of Pd²⁺ was 41 nM (7.2 ppb) which was lower than the WHO recommended value. Mass spectrum and Job's plot revealed 1:1 binding ratio. Both FESEM and DLS studies manifested the decrease of particle size of L₁ upon interaction with Pd²⁺ ion. ¹H NMR titration data were consistent with binding of Pd²⁺ to nitrogen atom of (CHN) group and IR spectra revealed coordination by sulphur of carbothioamide group. DFT/TDDFT calculations performed on L₁ and [Pd(L₁)(NO₃)₂] supported the experimental results very well. Probe L₁ was also found to be suitable for the recognition of Pd²⁺ in real water and pharmaceutical drug samples. Paper strips for on-spot analysis and testing and a symmetric 2D sensor device were also constructed.