M. A. N. Razvi

Microwave assisted synthesis, spectroscopic studies and non linear optical properties of bis-chromophores

Bis chromophores were synthesized by the terephthalaldehyde with (4-nitrophenyl) acetonitrile/(4-flurophenyl) acetonitrile under microwave irradiation. Bis-chromophores were obtained in good to excellent yields. The structures of bis-chromophores were established by FT-IR, (1)H NMR, (13)C NMR, EI-MS and elemental analyses. Physical chemical properties such as singlet absorption, extinction coefficient, stokes shift, oscillator strength and dipole moment, were investigated by UV-Vis and fluorescence spectroscopy measurements. Further we also measured the nonlinear refractive index and nonlinear absorption coefficients of these compounds using the single beam z-scan technique with a cw argon ion laser at 514.5 nm at different concentrations in DMSO solvent. The third order nonlinear susceptibility was estimated from these measurements and it shows high nonlinearity. The high negative refractive index makes these compounds suitable for optical limiting application.

Synthesis, linear and nonlinear optical properties of a new dimethine cyanine dye derived from phenothiazine

Dimethine cyanine dye (PTZIS) based on phenothiazine as the core donor and indolium salt as the acceptor has been synthesized and fully characterized. UV-Vis absorption and fluorescence properties of PTZIS were studied in different solvents. Absorption spectra revealed a large bathochromic shift of the intramolecular charge transfer (ICT) absorption band of PTZIS compared with those in the non-halogenated solvents. Also, the optical data of PTZIS showed a large Stokes shift compared with those in the non-halogenated solvents, indicating a great influence on the geometry of the emissive excited state. The nonlinear optical properties of PTZIS in ethanol solution at different concentrations and different laser powers have been studied using the Z-scan technique with a continuous wave (cw) argon ion laser at 514.5 nm. The closed aperture Z-scan data was used to estimate the nonlinear refractive index n2, while the open aperture scan provided the nonlinear absorption coefficient β. The values obtained are relatively very high and vary linearly with concentration.

Synthesis, Spectrofluorometric Studies, Micellization and non Linear Optical Properties of Blue Emitting Quinoline (AMQC) Dye.

Blue emitting 2-amino-4-(3, 4, 5-tri methoxyphenyl)-9-methoxy-5,6 dihydrobenzo[f]isoquinoline-1-carbonitrile (AMQC) dye was synthesized by one-pot multicomponent reactions (MCRs) of 3,4,5-trimethoxybenzaldehyd, malononitrile, 6-methoxy-1,2,3,4-tetrahydro-naphthalin-1-one and ammonium acetate. Results obtained from spectroscopic and elemental analysis of synthesized AMQC was in good agreement with their chemical structures. Fluorescence polarity study demonstrated that AMQC was sensitive to the polarity of the microenvironment provided by different solvents. In addition, spectroscopic and physicochemical parameters, including electronic absorption, excitation coefficient, stokes shift, oscillator strength, transition dipole moment and fluorescence quantum yield were investigated in order to explore the analytical potential of AMQC. Dye undergoes solubilization in different micelles and may be used as a quencher and a probe to determine the critical micelle concentration (CMC) of SDS and CTAB. Nonlinear optical parameters of AMQC dye shows relatively lower nonlinear refractive index and nonlinear absorption coefficient at the power levels. Variation of n2 with concentration is linear in the concentration range used in the present study.

Scattering properties of PT-symmetric objects

We investigate the scattering response of parity-time (PT) symmetric structures. We show that, due to the local flow of energy between gain and loss regions, such systems can deflect light in unusual ways, as a function of the gain/loss contrast. Such structures are highly anisotropic and their scattering patterns can drastically change as a function of the angle of incidence. In addition, we derive a modified optical theorem for PT-symmetric scattering systems, and discuss its ramifications.

Enhanced UV upconversion emission using plasmonic nanocavities

Strongly enhanced upconversion emission is experimentally demonstrated from an ensemble of β-NaYF₄:Gd³⁺/Yb³⁺/Tm³⁺ @NaLuF₄ core-shell nanoparticles trapped in judiciously designed plasmonic nanocavities. Using cross-shape silver nanocavities, 170-fold enhancement is obtained at UV band around 345 nm.

The durability of a hydroxyapatite paste used in decreasing the permeability of hypersensitive dentin.

Objectives Various agents are currently available for treatment of hypersensitive dentine, however, their resistance to erosion intraorally by various erosive drinks is still questionable. The aim of this study is to test the efficacy of a hydroxyapatite paste to decrease dentine permeability and resist an erosion challenge. Methods Hydroxyapatite powder was mixed with 25% phosphoric acid to form a paste which was applied on dentine having patent dentinal tubules orifices (treated with EDTA, 2 min) and the resulting layer formed on top of dentine was irradiated by Nd:YAG laser. The treated dentin surfaces were exposed to erosion challenge (6% citric acid, 1 min). Dentine permeability was measured before/after the application of the hydroxyapatite paste before/after the erosion challenge before/after the application of Nd:YAG laser using a split chamber device. The top and the fractured dentine surfaces were examined with scanning electron microscope (SEM). Moreover, the chemical nature of the compounds formed on top of dentine surface was examined using the SEM equipped with energy- dispersive X-ray spectroscope (EDS) and FTIR/ATR (Attenuated Total Reflectance Fourier Transform Infrared) techniques. The Mann-Whitney test (p < 0.05) was used to compare the effects of using the hydroxyapatite paste on dentine permeability and calcium/phosphate ratio of the treated dentine surfaces. Results The application of the hydroxyapatite paste to dentine significantly decreased dentine permeability (p < 0.05). Hydroxyapatite paste was able to occlude patent dentinal tubule orifices with a layer of calcium-phosphate compounds and the application of Nd:YAG laser on the aforementioned layer improved its erosion resistance. Conclusion Hydroxyapatite paste applied with the technique adopted in the current study has a high potential to be a useful aid in the treatment of dentine hypersensitivity. However, cost and knowledge for using Nd:YAG laser are important factors should be taken into consideration before using the aforementioned technique.

Physicochemical and Nonlinear Optical Properties of Novel Environmentally Benign Heterocyclic Azomethine Dyes: Experimental and Theoretical Studies.

Novel heterocyclic azomethine dyes were prepared by the reaction of anthracene-9-carbaldehyde with different heterocyclic amines under microwave irradiation. Structures of the azomethine dyes were confirmed by the elemental analysis, mass spectrometry and several spectroscopic techniques. We studied absorbance and fluorescence spectra of the azomethine dyes in various solvents. They are found to be good absorbers and emitters. We also report photophysical properties like, extinction coefficient, oscillator strength, stokes shift and transition dipole moment. This reflects physicochemical behaviors of synthesized dyes. In addition, their intramolecular charge transfer and nonlinear optical properties, supported by natural bond orbital technique, were also studied computationally by density functional theory. The negative nonlinear refractive index and nonlinear absorption coefficient were measured for these dyes using the closed and open aperture Z-scan technique with a continuous wave helium-neon laser. These are found to vary linearly with solution concentration.

Passive PT-Symmetric Metasurfaces With Directional Field Scattering Characteristics

We show that passive parity-time (PT) symmetric metasurfaces can be utilized to appropriately engineer the resulting far-field characteristics. Such PT-symmetric structures are capable of eliminating diffraction orders in specific directions, while maintaining or even enhancing the remaining orders. A systematic methodology is developed to implement this class of metasurfaces in both one-dimensional and two-dimensional geometries. In two-dimensional systems, PT symmetry can be established by employing either H-like diffractive elements or diatomic oblique Bravais lattices.