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

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 lambda(max-ab) = 516 nm to lambda(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 mu M using the fluorescence spectra changes, which is far lower than the WHO guideline of 1.9 mu M.