Aggregation induced emission active pyrene scaffold for real-time chromogenic and fluorogenic selective detection of Pd2+ ion and device fabrication

Abstract

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.