Resonance-assisted hydrogen bonding induced nucleophilic addition to hamper ESIPT: ratiometric detection of cyanide in aqueous media

For ratiometric "naked eye" detection of CN(-), an ESIPT exhibiting benzothiazole receptor (BHI) is designed having one aldehyde group ortho and the other aldehyde para to the OH group respectively. Due to RAHBs, the ortho aldehyde group is highly reactive undergoing nucleophilic cyanide addition selectively, which hampered ESIPT. This is also supported by DFT and TD-DFT calculations.