A cyanide-selective colorimetric “naked-eye” and fluorescent chemosensor based on a diketopyrrolopyrrole–hydrazone conjugate and its use for the design of a molecular-scale logic device

Abstract

A novel diketopyrrolopyrrole (DPP)–hydrazone based receptor 1 was designed and synthesized as a selective fluorescent and colorimetric chemosensor for cyanide without interference from other common anions including fluoride and acetate. The spectral responses of 1 to cyanide were studied: an approximately 130 nm red shift in absorption spectra (from λ_max-ab = 516 nm to λ_max-ab = 646 nm and the color change from pink to indigo) and “turn-off” emission response was observed. The experimental results revealed that the formation of anionic species from deprotonation of the hydrazone N–H moiety by cyanide was responsible for the spectral changes. Density function theory calculations were conducted to rationalize the optical response of the receptor 1. In the presence of cyanide, receptor 1 could act as an “Off–On” fluorescent probe for trifluoroacetic acid (TFA) based on the reversible protonation process, which may be represented by a complementary “IMPLICATION/INHIBIT” logic gate at the molecular level employing CN⁻–TFA as the chemical inputs. The detection limit was 0.23 μM using the fluorescence spectra changes, which is far lower than the WHO guideline of 1.9 μM.