Gobinda Prasad Sahoo

Pyrene Scaffold as Real-Time Fluorescent Turn-on Chemosensor for Selective Detection of Trace-Level Al(III) and Its Aggregation-Induced Emission Enhancement

A pyrene based fluorescent probe, 3-methoxy-2-((pyren-2yl-imino)methyl)phenol (HL), was synthesized via simple one-pot reaction from inexpensive reagents. It exhibited high sensitivity and selectivity toward Al(3+) over other relevant metal ions and also displayed novel aggregation-induced emission enhancement (AIEE) characteristics in its aggregate/solid state. When bound with Al(3+) in 1:1 mode, a significant fluorescence enhancement with a turn-on ratio of over ∼200-fold was triggered via chelation-enhanced fluorescence through sensor complex (Al-L) formation, and amusingly excess addition of Al(3+), dramatic enhancement of fluorescence intensity over manifold through aggregate formation was observed. The 1:1 stoichiometry of the sensor complex (Al-L) was calculated from Jobs plot based on UV-vis absorption titration. In addition, the binding site of sensor complex (Al-L) was well-established from the (1)H NMR titrations and also supported by the fluorescence reversibility by adding Al(3+) and EDTA sequentially. Intriguingly, the AIEE properties of HL may improve its impact and studied in CH3CN-H2O mixtures at high water content. To gain insight into the AIEE mechanism of the HL, the size and growth process of particles in different volume percentage of water and acetonitrile mixture were studied using time-resolved photoluminescence, dynamic light scattering, optical microscope, and scanning electron microscope. The molecules of HL are aggregated into ordered one-dimensional rod-shaped microcrystals that show obvious optical waveguide effect.

Enhanced photocatalytic activity of metal coated ZnO nanowires.

A simple, facile and template free route has been described for the synthesis of ZnO nanowires. The morphology and structure of ZnO nanowires have been tuned by deposing silver and gold onto the surface of ZnO nanowire and this has been done by adding AgNO(3) and HAuCl(4) to aqueous suspension of ZnO. Our synthesized Ag and Au coated ZnO nanoparticles show different emissive property than the native ZnO nanowires. The photocatalytic degradation of Methylene Blue is also evaluated using ZnO and Ag and Au coated ZnO nanowires. It has been observed that Ag coated ZnO nano-needles exhibits significantly enhanced photocatalytic efficiency compare to ZnO nanowire and Au coated ZnO nano-leaves. Fluorescence spectra and surface structure of the samples with their photocatalytic activity indicates that surface deposited metal serves as an electron sinks to enhance the separation of photoinduced electrons from holes, leading to the formation of OH and it enhances their photocatalytic efficiency.

Aqueous-Phase Synthesis of Silver Nanodiscs and Nanorods in Methyl Cellulose Matrix: Photophysical Study and Simulation of UV-Vis Extinction Spectra Using DDA Method

We present a very simple and effective way for the synthesis of tunable coloured silver sols having different morphologies. The procedure is based on the seed-mediated growth approach where methyl cellulose (MC) has been used as soft-template in the growth solution. Nanostructures of varying morphologies as well as colour of the silver sols are controlled by altering the concentration of citrate in the growth solution. Similar to the polymers in the solution, citrate ions also dynamically adsorbed on the growing silver nanoparticles and promote one (1-D) and two-dimensional (2-D) growth of nanoparticles. Silver nanostructures are characterized using UV–vis and HR-TEM spectroscopic study. Simulation of the UV–vis extinction spectra of our synthesized silver nanostructures has been carried out using discrete dipole approximation (DDA) method.

DFT based computational study on the excited state intramolecular proton transfer processes in o-hydroxybenzaldehyde

Potential energy (PE) curves for the intramolecular proton transfer in the ground (GSIPT) and excited (ESIPT) states of o-hydroxybenzaldehyde (OHBA) were studied using DFT-B3LYP/6-31G(d) and TD-DFT-B3LYP/6-31G(d) level of theory, respectively. Our calculations suggest the non-viability of ground state intramolecular proton transfer in this compound. Excited states PE calculations support the ESIPT process in OHBA. The contour PE diagram and the variation of oscillator strength along the proton transfer co-ordinate support the dual emission in OHBA. Our calculations also support the experimental observations of Nagaoka et al. [S. Nagaoka, U. Nagashima, N. Ohta, M. Fujita, T. Takemura, J. Phys. Chem. 92 (1988) 166], i.e. normal emission of the title compound comes from S(2) state and the red-shifted proton transfer band appears from the S(1) state. ESIPT process has also been explained in terms of HOMO and LUMO electron density of the enol and keto tautomer of OHBA and from the potential energy surfaces.

Morphology directing synthesis of 1-pyrene carboxaldehyde microstructures and their photo physical properties

Morphologically interesting organic microstructures from 1-pyrene carboxaldehyde (1-PyCHO) have been synthesized using sodium dodecyl sulphate (SDS) as a morphology directing agent. Here we have presented a re-precipitation method to synthesize rod, bar and rectangular plate shaped microstructures from 1-PyCHO. The morphology of the materials has been characterized using optical microscopy, SEM and XRD measurements. UV-Vis absorption, steady state and time resolved fluorescence emission techniques are used to study the photophysical behaviour of the aggregated structures of 1-PyCHO. Computation of the second order Fukui parameter as a local reactivity descriptor (LRD) on each atomic centre of 1-PyCHO suggests that two nearest 1-PyCHO molecules are arranged in face to face slipped conformations in their aggregated structures. Our computational results are in conformity with the single crystal data of 1-PyCHO and this is the first time that LRD is used to explain the stacking pattern of similar kinds of molecules.

Crystal induced phosphorescence from Benz(a)anthracene microcrystals at room temperature.

Pure organic compounds that are also phosphorescent at room temperature are very rare in literature. Here, we report efficient phosphorescence emission from aggregated hydrosol of Benz(a)anthracene (BaA) at room temperature. Aggregated hydrosol of BaA has been synthesized by re-precipitation method and SDS is used as morphology directing agent. Morphology of the particles is characterized using optical and scanning electronic microcopy (SEM). Photophysical properties of the aggregated hydrosol are carried out using UV-vis, steady state and time resolved fluorescence study. The large stoke shifted structured emission from aggregated hydrosol of BaA has been explained due to phosphorescence emission of BaA at room temperature. In the crystalline state, the restricted intermolecular motions (RIM) such as rotations and vibrations are activated by crystal lattice. This rigidification effect makes the chromophore phosphorescent at room temperature. The possible stacking arrangement of the neighboring BaA within the aggregates has been substantiated by computing second order Fukui parameter as local reactivity descriptors. Computational study also reveals that the neighboring BaA molecules are present in parallel slipped conformation in its aggregated crystalline form.

Microwave-assisted synthesis of anisotropic gold nanocrystals in polymer matrix and their catalytic activities

We report a facile and fast one-pot microwave (MW) synthesis of gold nanotriangle, nanobranches and nanorod. Gold salt is reduced to gold nanoparticles by ethylene glycol/polyethylene glycol in the presence of hydroxypropyl methyl cellulose. Morphology of the nanocrystals can be tailored by varying the amount of capping agents, reducing agent and the MW irradiation time. Synthesised nanoparticles are characterised by ultraviolet–visible (UV–Vis), transmission electron microscopic and X-ray diffraction spectroscopy study. The key requirement for producing the gold triangle and gold nanorod of higher aspect ratio is the adequate MW heating time. The photocatalytic activity of gold nanocrystals is investigated by monitoring the photochemical reduction of 2,4,6-trinitrophenol (TNP) in the presence of excess NaBH4. The reaction is first order with respect to the concentration of TNP. It has been observed that the catalytic efficiency of rod-like gold nanocrystals is higher than the other gold nanocrystals.

Synthesis of gold nanoparticles of variable morphologies using aqueous leaf extracts of Cocculus hirsutus

Spherical, triangular (prismatic) and square plate shaped gold nanoparticles have been synthesised from HAuCl4 · 3H2O solution using the aqueous leaf extract of Cocculus hirsutus. Nanoparticles are characterised using higher resolution transmission electron microscope, X-ray diffraction and UV–Vis absorption spectroscopic study. FT-IR analysis reveals that the gold nanostructures are mostly stabilised by the carbonyl and amide groups present in the active component of C. hirsutus leaf extract. Formation of gold nanostructures of variable morphologies has been explained due to slow reduction of gold ions by the mild reducing ascorbic acid present within the extract and this controlled reduction assists the preferential deposition of Au atom on different lesser-protected faces of initially grown gold nanostructure.

Solution-phase synthesis of silver nanodiscs in HPMC-matrix and simulation of UV-vis extinction spectra using DDA based method.

Present investigation demonstrates a very simple seed-mediated route, using hydroxypropyl methyl cellulose (HPMC) as stabilizing agent, for the synthesis of silver nanodiscs in aqueous solution. Central to the concept of seed-mediated growth of nanoparticles is that small nanoparticle seeds serve as nucleation centres to grow nanoparticles to a desired size and shape. It is found that the additional citrate ions in the growth solution play the pivotal role in controlling the size of silver nanodiscs. Similar to the polymers in the solution, citrate ions could be likewise dynamically adsorbed on the growing silver nanoparticles and promote the two-dimensional (2D) growth of nanoparticles. Morphological, structural, and spectral changes associated with the seed-mediated growth of the nanoparticles in the presence of HPMC are characterized using UV-vis and TEM spectroscopic studies. Metal nanoparticles have received increasing attention for their peculiar capability to control local surface plasmon resonance (LSPR) when interacting with incident light waves. Extensive simulation study of the UV-vis extinction spectra of our synthesized silver nanodiscs has been carried out using discrete dipole approximation (DDA) methodology.