Experimental and theoretical studies of novel hydroxynaphthalene based chemosensor, and construction of molecular logic gates

TD-DFT investigation on anion recognition mechanism of anthraldehyde-based fluorescent thiosemicarbazone derivatives

The mechanism of host-guest interaction of receptors towards fluoride ion has been investigated using computational methods. To distinguish the effect of aromaticity in host-guest interaction, we investigated unsubstituted (ATSC) and phenyl-substituted (APTSC) anthracene thiosemicarbazones towards different ions. In the ground state of receptor-fluoride complex, the added fluoride ion made hydrogen bond through N - H^…F^…H - N, whereas the intramolecular hydrogen bonding was through F - H^…N in the excited state of receptor-fluoride complex. Experimental absorption and emission spectra were well reproduced by the calculated vertical excitation energies. The transition state (TS) calculations were performed to understand the thermodynamic features and mechanism of host-guest interaction. The natural bond orbital analyses show that the second perturbation energy for donor-acceptor interaction of F^- with hydrogen is more than 300 kcal/mol^-1 at the excited state of receptor-fluoride complex, which indicates the strong single bond between fluoride and hydrogen atom. The PES scan confirms that deprotonation took place at the excited state of receptor-fluoride complex. The results indicate the excited-state proton transfer (ESPT) process from N-H group nearby the anthracene moiety. The APTSC is a better chemosensor than ATSC. This infers that the aromaticity will increase the efficiency of fluorescence receptor towards fluoride ion. A schematic representation of sensing mode of anthracene-based thiosemicarbazones toward fluoride ion. The fluoride ion first makes a hydrogen bond with NH proton nearby anthracene moiety. The excited state proton transfer mechanism was confirmed by PES and NBO studies.

A spectroscopic probe for hypochlorous acid detection

A spectroscopic probe CMBT was synthesized and characterized. CMBT showed the specific recognition for HClO based on the turn-on blue fluorescence and naked-eye change from pink to colorless. NMR, IR, HRMS-ESI, and spectral analysis suggested that colorimetric and fluorescent change of CMBT to HClO originated from the conversion of CMBT to starting material coumarin-aldehyde 1 caused by the oxidization of HClO, which was responsible for the fluorescence recovery. The detection limit was calculated to be 1.61 μM and 6.58 μM for fluorescence and UV-vis analysis with a range up to 1 mM. HClO's fluorescence detection was successfully achieved in tap and river water samples. The prepared convenient paper test strips showed a distinct color change in varying concentrations of HClO. A multi-input molecular logic circuit was constructed.

"Switch on" fluorescent sensor for the detection of fluoride ions in solution and commercial tooth paste

A simple and novel uracil based chemosensor (1) has been developed by one step reaction, which selectively detected F^- ions via "switch on" fluorescence mode. Upon the addition of F^- ion to CH₃CN solution of 1, the non-fluorescent probe became highly fluorescent, showing a color change from colorless to fluorescent blue, when irradiated with 280nm light. ¹H NMR studies revealed the binding sites of chemosensor 1, where C-5 hydrogen and amine hydrogens formed hydrogen bonding with F^- ion. This binding mode was further confirmed using DFT calculations. Significantly, the detection limit of chemosensor 1 towards F^- has been evaluated to be 47.6nM, which is lower than the maximum values of F^- (1.5mg/L) ions permitted by WHO. The in-situ generated 1-F^- complex has been used for secondary sensing of Ca(NO₃)₂, one of the component of the fertilizer. Moreover, the sensor has been successfully applied for detection of fluoride ion in commercial tooth paste.

The crystal structure of ((cyclo-hexyl-amino){(Z)-2-[(E)-5-meth-oxy-3-nitro-2-oxido-benzyl-idene-κO]hydrazin-1-yl-idene-κN 2}methane-thiol-ato-κS)(dimethyl sulfoxide-κS)platinum(II): a supra-molecular two-dimensional network

The PtII atom in the title complex, [Pt(C15H18N4O4S)(C2H6OS)], exists within a square-planar NS2O donor set provided by the N, S, O atoms of the di-anionic tridentate thio-semicarbazo ligand and a dimethyl sulfoxide S atom. The two chelate rings are coplanar, subtending a dihedral angle of 1.51 (7)°. The maximum deviation from an ideal square-planar geometry is seen in the five-membered chelate ring with an S-Pt-S bite angle of 96.45 (2)°. In the crystal, mol-ecules are linked via N-H⋯O, C-H⋯O, C-H⋯N and C-H⋯π inter-actions into two-dimensional networks lying parallel to the ab plane. The conformations of related cyclo-hexyl-hydrazine-1-carbo-thio-amide ligands are compared to that of the title compound.

Crystal structure of (E)-N-cyclo-hexyl-2-(2-hy-droxy-3-methyl-benzyl-idene)hydrazine-1-carbo-thio-amide

The asymmetric unit of the title compound, C15H21N3OS, comprises of two crystallographically independent mol-ecules (A and B). Each mol-ecule consists of a cyclo-hexane ring and a 2-hy-droxy-3-methyl-benzyl-idene ring bridged by a hydrazinecarbo-thio-amine unit. Both mol-ecules exhibit an E configuration with respect to the azomethine C=N bond. There is an intra-molecular O-H⋯N hydrogen bond in each mol-ecule forming an S(6) ring motif. The cyclo-hexane ring in each mol-ecule has a chair conformation. The benzene ring is inclined to the mean plane of the cyclo-hexane ring by 47.75 (9)° in mol-ecule A and 66.99 (9)° in mol-ecule B. The mean plane of the cyclo-hexane ring is inclined to the mean plane of the thio-urea moiety [N-C(=S)-N] by 55.69 (9) and 58.50 (8)° in mol-ecules A and B, respectively. In the crystal, the A and B mol-ecules are linked by N-H⋯S hydrogen bonds, forming 'dimers'. The A mol-ecules are further linked by a C-H⋯π inter-action, hence linking the A-B units to form ribbons propagating along the b-axis direction. The conformation of a number of related cyclo-hexa-nehydrazinecarbo-thio-amides are compared to that of the title compound.

Development of three ways molecular logic gate based on water soluble phenazine fluorescent 'selective ion' sensor

New hydrophilic fluorescent selective ion sensor based on phenazine and phthalazine moieties, 1,1'-(phenazine-2,3-diyl)-bis(3-(1,4-dihydroxyphthalazin-6-yl)urea) (1), has been designed, synthesized and characterized. Interestingly, sensor 1 exhibits prominent "turn-on" and "turn-off" fluorogenic signaling at 580 nm towards Fe²⁺ & AcO^- and Sr²⁺ & Cu²⁺, respectively. The fluorescence titration experiments shed light on the nature of the interaction between 1 and guest molecules (Fe²⁺, Sr²⁺, Cu²⁺ and AcO^-), which divulge that 1 is flexible enough to orient itself according to the size of the guest molecule. Water mediated excited-state intramolecular proton transfer (ESIPT) and photo-induced electron transfer (PET) mechanisms are responsible for the dual behavior of 1, which binds with guest molecules in 1:1 stoichiometry. Based on the significant duplex fluorescence response of 1, a molecular logic gate keypad lock with sixteen "on" passwords for a storage system has been developed.

A new disulfide Schiff base as a versatile “OFF–ON–OFF” fluorescent–colorimetric chemosensor for sequential detection of CN− and Fe3+ ions: combined experimental and theoretical studies

A new disulfide Schiff base as a versatile “OFF–ON–OFF” fluorescent–colorimetric chemosensor has been synthesized for sequential detection of CN⁻ and Fe³⁺ ions.

Crystal structure of (E)-2-[3-(tert-but-yl)-2-hy-droxy-benzyl-idene]-N-cyclo-hexyl-hydrazine-1-carbo-thio-amide

In the title compound, C18H27N3OS, the cyclo-hexane ring has a chair conformation. The azomethine C=N double bond has an E configuration. The nearly planar hydrazinecarbo-thio-amide moiety and substituted benzene ring are twisted by 31.13 (5)° relative to each other. The amide moiety and the cyclo-hexane ring are almost perpendicular to each other; a similar conformation was previously observed in reported structures. In the crystal, mol-ecules are linked by N-H⋯S hydrogen bonds, forming inversion dimers with an R 2 2(8) ring motif.

New insights into the sensing mechanism of a phosphonate pyrene chemosensor for TNT

As security needs have increased, mechanism investigation has become of high importance in the development of new sensitive and selective chemosensors for chemical explosives. This study details a theoretical investigation of the sensing mechanism of a new phosphonate pyrene chemosensor for trinitrotoluene (TNT), suggesting a different interaction mode between the probe and TNT from the one previously reported. The invalidity of the mechanism of binding TNT through intermolecular hydrogen bonds was proved using the Gibbs free energy profile and 1H NMR analysis. Frontier molecular orbitals (FMOs) analysis was used to show that photo-induced electron transfer (PET) is the underlying mechanism behind the luminescence quenching of the probe upon exposure to TNT, the rationality of which was further confirmed by the recording of a high charge transfer rate. We also found the existence of an energy level crossing between the local excited (LE) state and charge transfer (CT) state of a complex of the probe and TNT, which was confirmed using energy profile calculations along the linearly interpolated internal coordinate (LIIC) pathway.

Multi-ion detection and molecular switching behaviour of reversible dual fluorescent sensor

The selective chemosensing behaviour of imidazole bisthiocarbohydrazone (IBTC) towards F^- and Cu²⁺ are studied via colorimetric, UV-Visible, fluorescence spectra studies, and binding constants were calculated. The ¹H NMR titration study strongly support that the deprotonation of IBTC followed by the hydrogen bond formation via N1H1 and N2H2 protons with fluoride ion. The fluorescence inactive IBTC-Cu complex became fluorescence active in the presence of perchlorate (ClO₄^-) ion. The selective detection of perchlorate ion was also explained. The F^- sensing mechanism of IBTC has been investigated by Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TDDFT) methods. The theoretical outcomes well reproduce the experimental results. And it concluded the NH protons, nearby the imine group was first captured by the added F^- ion and then deprotonation happened followed by the formation of hydrogen bond. The IBTC found good reversibility character with the alternative addition of Ca²⁺ and F^-. The multi-ion detection of IBTC was used to construct the NOR, OR and INHIBITION molecular logic gates.