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 2nd and 4th 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.

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.

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 bis­copper cryptate 1 via ideal linear orientation of N4-Cu⋯N3⋯Cu-N4 axle inside the cylindrical shaped cavity.

A molecular phototropic system for cyanide: Detection and sunlight driven harvesting of cyanide with molecular sunflower.

We are reporting a simple, easy to prepare, and conformation switchable first molecular phototropic system L, "(E)-2-(2,4-dinitrophenyl)-1-((pyren-8-yl)methylene)hydrazine, for cyanide harvesting. This molecular phototropic system behaves as a molecular sunflower in which the conformation of this molecular sunflower can be altered in response to the sunlight. This molecular flower can sense and bind the cyanide anion colorimetrically through its transition state. Further, upon exposure of this transition state cyanide complex 1, under sunlight, this system is capable to release the bound cyanide via -C=N- free rotation to reach its lower energy stable conformation. Similar behaviors were observed for acetate and fluoride with L. The strength of the phototropic system L towards cyanide, acetate and fluoride is found to be 4.5 × 105, 1.53 × 102 and 6.09 × 102 M-1.

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.

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.

Here in we report tris (3-aminopropyl) amine based tripodal receptors L, L1 and L2 which were functionalized with 4-nitrophenyl moieties having thio-urea, amide and sulfonamide as hydrogen bonding moieties respectively, shows a strong selectivity towards cyanide. A competitive colorimetric assay with L in the presence of fluoride ion suggests that the cyanide ion is much capable of displacing the bound fluoride, showing a sharp distinguishable color change. To the best of our knowledge, this is the first example of a naked-eye detection of cyanide via fluoride displacement assay by a tripodal receptor and such a displacement phenomenon is not observes in the cases of L1 and L2, instead the receptor L1 binds nitrate and cyanide; L2 binds dihydrogen phosphate and cyanide. Using this assay, we have proposed an AND logic gate using L·F- and CN-.

Hydrogen bonding elements, π - hole functional moieties and C3v tripodal scaffold controlled turn-on cyanide and turn-off azide selective receptors.

Here in, we are reporting electron deficient amide and sulfonamide based tripodal receptors L, L1, L2 and L3. Systematic studies show a strong selectivity towards cyanide and azide anions. Detailed UV-Visible and fluorescent spectrometric investigation shows the amide based tripodal receptors L and L3 acts as a colorimetric and turn-on fluorescent chemo-sensor for cyanide, and the sulfonamide based tripodal receptors L1 and L2 acts as a colorimetric and turn-off fluorescent chemo-sensor for azide. At the end we have successfully prepared tripodal receptors for a particular anion with judicious choice of recognition elements such as hydrogen bonding amide/sulfonamide moiety, electron deficient pentafluorophenyl functionality for anion-π interaction and the well defined C3v symmetric tripodal backbone for perfect recognition.

Tuning the recognition properties of urea based receptor towards cyanide in aqueous medium: Effect of fluorine substitution on strength and selectivity of the anion receptor.

In this report, we have successfully tuned the selectivity and sensitivity of an anion receptor L1 by substituting electron withdrawing natured fluorine atoms directly on to the rim of the phenyl ring. Despite the fact that, we have two electron withdrawing natured nitro substituents on the other side of receptor L1; two fluorine substitutions made dramatic change in the sensing ability as well as the selectivity of the receptor L1 towards anions. The acetonitrile solution contains L1 with tetrabutyl ammonium salts of fluoride, cyanide, acetate and dihydrogen phosphate results sudden color changes from yellow to brown; almost negligible spectral/color change for azide and bifluoride, where as there is no color change observed with any other anionic guests with L1. Solution state binding studies of L1 are carried out by UV-Vis spectrometry titration in 100% acetonitrile and it is found to be the receptor L1 selectively binds cyanide, phosphate and fluoride stronger than acetate; it is also found that receptor binds fluoride 100 times stronger than that of the receptor L and L1 has almost similar efficiency in binding towards acetate ion (AcO-). The strength of the receptor L1 towards fluoride, cyanide, acetate and dihydrogen phosphate bindings are found to be in the order of 1.271 × 105 M-1 > 1.245 × 105 M-1 > 1.368 × 103 M-1, 1.23 × 103 M-1 respectively. When we used aqueous environment (10% of water in acetonitrile) as testing solvent system, the receptor L1 selectively sense cyanide ion. Over all, strength of the receptor is increased towards anions with an increasing the number of fluorine atom onto the receptors. Here in we have also prepared a reference compound L2 in which the receptor molecule is substituted with only one fluoride atom. The acetonitrile solution of reference receptor L2 with help of naked-eye colorimetric experiment and spectrometric ammonium salts of fluoride, cyanide, acetate and bifluoride results sudden color changes from faint-yellow to brown in color. Unlike receptor L1, receptor L2 does not recognize H2PO4-, but instead of H2PO4-, it recognizes bifluoride as evidenced from UV-Vis spectroscopic and naked-eye colorimetric studies.

Simple and highly electron deficient Schiff-base host for anions: First turn-on colorimetric bifluoride sensor.

Here in, we have designed, synthesized and isolated sensor L, as a turn-on colorimetric chemo sensor for bifluoride ion. The acetonitrile solution contains L with tetrabutyl ammonium salts of bifluoride, cyanide and fluoride results sudden color changes from yellow to dark brown where as there is no color change observed with any other anionic guests with L. Solution state binding studies of L are carried out by UV-Vis spectrometry titration and the strengths of the chemosensor L towards bifluoride, cyanide and fluoride bindings are found to be 2.67 × 105 M-1, 4.78 × 105 M-1, 4.45 × 105 M-1 respectively. The strength and sensitivity of the absorbance based assay with L for bifluoride ion, are found to be 2.67 × 105 M-1 and 0.7 µM respectively, which is the best (highest binding constant and lowest LOD) ever reported in the literature. In order to use this sensor in practical application, we also prepared a cassette which is fabricated with sensor L and we succeeded to sense bifluoride ion.

Electron-deficient tripodal amide based receptor: An exclusive turn-on fluorescent and colorimetric chemo sensor for cyanide ion.

Here in, we have designed, synthesized and isolated sensor L, as an exclusive selective turn-on fluorescent chemo sensor for cyanide ion. The acetonitrile solution contains L with tetrabutyl ammonium cyanide, results sudden color change from colorless to yellowish-brown. Chemosensor L produced a strong fluorescence response with an enhancement of very high fluorescence intensity while addition of CN- ion and the strength of the chemosensor L towards cyanide binding is found to be 3.9813×104M-1. In order to use this sensor in practical application, we also prepared a cassette which is fabricated with sensor L and we succeeded to sense cyanide ion.