Commercial trans-β-nitrostyrene analogues for colorimetric cyanide (CN−) detection via Michael addition-based chemodosimetric approach validated by comparative investigations, DFT, and strip method

Abstract

Using commercial materials for colorimetric detection of toxic cyanide (CN⁻) anions can greatly improve safety and benefit society. This work discusses the colorimetric sensing properties of commercially available trans-β-nitrostyrene analogues, including trans-β-nitrostyrene (P1), trans-4-methoxy-β-nitrostyrene (P2), trans-4-methyl-β-nitrostyrene (P3), trans-4-fluoro-β-nitrostyrene (P4), trans-4-bromo-β-nitrostyrene (P5), trans-4-chloro-β-nitrostyrene (P6), and trans-β-methyl-β-nitrostyrene (P7), in dimethyl sulfoxide (DMSO) and acetonitrile (ACN). P1-P4 show strong reddish-pink and yellowish-orange colors while detecting CN⁻ ions in DMSO and ACN, with new UV–visible peaks appearing at 515 nm/510 nm and at 490 nm/485 nm, respectively. Conversely, P5 and P6 exhibit mild color responses to CN⁻ in DMSO and ACN, with absorbance peaks at 505 nm/510 nm and at 490 nm/430 nm, respectively. P7 shows no selectivity for CN⁻ ions due to steric and electronic structural effects. The high selectivity of P1-P4 for CN⁻ is confirmed through interference studies. pH values of 6 and 7 are ideal for sensory testing. The sensor response of P1-P6 to CN⁻ is linear across a range of 0.1 to 1000 μM (μM = 10⁻⁶ M), with estimated detection limits (LODs) at 10⁻⁹–10⁻⁶ M. Nuclear Magnetic Resonance (NMR), mass spectra, and density functional theory (DFT) analyses validate the Michael addition as the sensing mechanism. The test strip method demonstrates the solid-state colorimetric sensing ability of P1-P3 for CN⁻ ions. Spiked CN⁻ ions in water samples show the real-time sensing capability of P1-P4. These results open the door for future designs using different fluorophores with nitro (-NO<inf>2</inf>) Michael acceptor.