Traditional hydrogen bonding donors controlled colorimetric selective anion sensing in tripodal receptors: First-naked-eye detection of cyanide by a tripodal receptor via fluoride displacement assay

Pyrene-Hydrazone-π···Hole Coupled Turn-on Fluorescent and Naked- Eye Colorimetric Sensor for Cyanide: Role of Homogeneous π-Hole Dispersion in Anion Selectivity

A pyrene based probe associated with π···hole - hydrazone as one of the recognizing elements is synthesized and its turn in to a selective colorimetric and turn-on fluorescent sensor, (L³) for cyanide anion. This chemo sensor show high selectivity towards cyanide anion through photo electron transfer (PET) mechanism. The binding strength and sensitivity of the chemo sensor L³ towards cyanide are found to be 2.0 X 10⁴, and 4.44 x 10^-4 respectively. We have compared this high selectivity of the receptor towards cyanide, with our previously reported receptors L¹ and L². The detailed UV-Vis, Emission, ¹H-NMR, IR spectroscopic and Molecular Electrostatic Potential (MEP) studies reveals that the homogeneous π···hole dispersion in the aromatic ring governing the selectivity of the receptor towards cyanide anion. Such a positive π···hole homogeneous dispersion is missing in the case of sensor L², instead we have polarized π···hole dispersion towards 2^nd and 4^th position of di-nitrophenyl chromophoric unit in L².

Anion-binding-induced and reduced fluorescence emission (ABIFE & ABRFE): A fluorescent chemo sensor for selective turn-on/off detection of cyanide and fluoride

A new hydrazine based π-hole assisted, electron deficient turn-on/off fluorescent and colorimetric sensor L with anion-binding induced/reduced fluorescent emission (ABIFE & ABRFE) has been designed and synthesized. The prepared sensor L exhibited excellent turn-on fluorescence emission in the presence of cyanide ion through ABIFE. On the other hand, the receptor L turns-off its fluorescence intensity upon binding with fluoride; however, the reduced emission intensity of this complex of L is recovered by addition of cyanide. The sensor L is almost intact with other tested anions. To the best of our knowledge, this is the first report on sensing of cyanide and fluoride by a neutral hydrazine based receptor via anion-binding-induced fluorescence emission (ABIFE) and anion-binding-reduced fluorescence emission (ABRFE) mechanisms respectively. The observed ABIFE and ABRFE phenomena of L with cyanide is further supported by UV-Vis, Emission, ¹H NMR and IR spectroscopic studies.

Selective colorimetric sensing and perfect linear recognition of azide: Formation of Cu-azide-Cu cascade complex within the cavity of cryptand

Bis-trpn [tris(3-aminopropyl)amine], capped dicopper complex of bicyclic cryptand L, 1, became a potential selective colorimetric chemosensor for azide anion. Complex 1 is generating a space inside the cylindrical cavity which will be opt for perfect linear recognition of azide anion through as N₄-Cu⋯N₃^-⋯Cu-N₄ axle. Naked eye colorimetric and UV-Vis spectrometric investigations shows the complex 1 has the capability of selective sensing of azide anion. The association constant and limits of detection (LoD) of complex 1 towards azide are found to be 2.754 × 10³ M^-1 and 1.91 × 10^-6 M. To the best of our knowledge, this is the first example of selective colorimetric sensing of azide by a bis‑copper cryptate 1 via ideal linear orientation of N₄-Cu⋯N₃⋯Cu-N₄ axle inside the cylindrical shaped cavity.

C3V symmetric tripodal molecular pocket for linear anions: Selective colorimetric detection of azide through N4-Cu-π···hole interactions

Tris(3-amino propyl)amine (TRPN) based C₃v symmetric tripodal molecular pocket, L has been prepared and mono copper complex of L, (1) having Cu-N₄-π··· hole as recognizing elements, becoming a potential and selective colorimetric chemo sensor for perfect linear recognition of N₃^-, generate a Cu-NNN- π··· hole unit inside the tripodal pocket. Systematic spectrometric and naked-eye colorimetric studies reveal that, this chemo sensor is also colorimetrically recognizing the cyanide ion by its cavity via Cu-N₄-π···hole interactions; nevertheless, when azide anion is entering as a guest into the molecular pocket of 1 which is already hosted cyanide anion, then host displaces cyanide ion, subsequently azide is getting inside the cavity. The strength of the copper complex, 1 towards azide and cyanide are found to be 2.36 × 10³M^-1, and 1.87 × 10³ M^-1 respectively in 7:3 acetonitrile:water solvent medium. Further, the ability of cyanide displacement by azide in complex 1 is found to be 2.53 × 10³ M^-1. To the best of our knowledge, this is the first example of naked-eye detection of azide via cyanide displacement assay by a tripodal receptor.

Most Efficient Tris(3-Aminopropyl) Amine Based Electron Deficient Tripodal Receptor for Azide

Investigation on strength of the tris(2-amino ethyl) amine and tris (3-amino propyl) amine backboned tripodal receptors, L and L¹ (incorporated with tripodal C₃ν frame, thio urea-amide linkage and π-hole assisting functionality) which are premeditated to explore the prospect for a particular anion recognition are studied. UV-Vis, ¹H- NMR, and IR spectroscopy studies indicates that both the receptors sensing azide anion, colorimetrically and binds azide anion stronger than any other anions such as acetate, and cyanide. In particular the receptor L¹ shows the highest binding strength towards azide anion. To the best of our knowledge this is the first receptor showing highest binding ability with azide anion. We used Molecular Electrostatic Potential Surface analyses to support our spectroscopic findings. The association constant and limits of detection for receptor L¹ with azide is found to be 8.4X10⁵M^-1 and 3.16X10^-6 M respectively. The observed highest binding strength of L¹ with azide is, could be due to the cooperative effect of extended traditional hydrogen bonding via thiourea-amide functionality, anion-π interaction and C₃ν suitable framework.