Colorimetric ‘turn on TBET’ sensors for ‘on the spot’ visual detection of HSO4− in semi-aqueous medium: Experimental and quantum chemical (DFT) studies

Abstract Indole appended tetrapodal and hexapodal receptors ( R1 and R2 ) exhibited a selective colorimetric on the spot response towards HSO 4 − ion in CH 3 CN H 2 O (1:1). The receptors showed visually detectable colour changes on applying the HSO 4 − ion. Sharp fluorescence intensity quenching for R1 and fluorescence enhancement for R2 were observed with HSO 4 − . The association constant ( K a ), determination of the stoichiometry and the large downfield shift of the N H and C2 H proton signals in the 1 H NMR experiments supported the complexation phenomenon through a TBET process. Quantum-chemical calculations and molecular modelling studies using Density Functional Theory (DFT) allowed estimating the energy optimized structures of the receptors and their complexes together with their probable binding mode for complexation.