Synthesis, Photo-physical and DFT Studies of ESIPT Inspired Novel 2-(2′,4′-Dihydroxyphenyl) Benzimidazole, Benzoxazole and Benzothiazole

Novel ESIPT inspired benzimidazole, benzoxazole and benzothiazole were synthesized from 2,4-dihydroxy benzoic acid and 1,2-phenelenediamine, 2-aminophenol, and 2-aminothiophenol respectively. The synthesized 2-(2′,4′-dihydroxyphenyl) benzimidazole, benzoxazole and benzothiazole are fluorescent and the emission characteristic are very sensitive to the micro-environment. They show a single absorption and dual emission with large Stokes shift originating from excited state intramolecular proton transfer. The absorption-emission characteristics of all these compounds are studied as a function of pH. The change in the electronic transition, energy levels, and orbital diagrams of synthesized compounds were investigated by the molecular orbital calculation and were correlated with the experimental spectral emission. Experimental absorption and emission wavelengths are in good agreement with those predicted using the Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) [B3LYP/6-31G(d)].

A Combined Experimental and DFT-TDDFT Study of the Excited-State Intramolecular Proton Transfer (ESIPT) of 2-(2′-Hydroxyphenyl) Imidazole Derivatives

We report a combined experimental and computational study of the effect of electron donor and acceptor groups on the excited state intramolecular proton transfer of 2-(2′-hydroxyphenyl) imidazole derivatives in solvents of different polarities. The changes in fluorescence properties, electronic transitions and energy levels are analyzed and discussed. The study was complemented using the Density Functional Theory (DFT)-Time Dependent DFT [B3LYP/6-31G(d)] computations. The calculated absorption and emission spectra of the imidazole derivatives are in good agreement with the experiments, thus allowing an assignment of the UV–vis spectra.     

Ab initio and anion photoelectron studies of Rhn (n = 1 − 9) clusters

We present an analysis of Na-He collisional profiles at high density and very low temperature in a unified line shape semi-classical theory which contains the impact as well the quasistatic limits. Clearly understanding the variation of shape of the two fine-structure components of the 3s?3p line with increasing helium density allows us to understand experimental spectra of a Na atom attached to He nanodroplets. We compare our collisional approach to path integral Monte Carlo calculations using the same ab initio Na-He molecular potentials.     

Designing of Optical Fiber Sensing Probe

Evanescent wave configuration has been extensively used in the development of fiber-optic sensor for different biomedical applications. In the present investigation we have theoretically proposed the designing of single-mode and multimode optical fiber sensing probes, which can be prepared by removing a few centimeters of cladding near the distal end of the step index optical fiber. In this theoretical study, we found that the removal of cladding causes V-number mismatching and this has led to the loss of signal acquisition from the sensing region. Therefore, to minimize these losses we have proposed to reduce the radius by step etch and tapering technique. It was found that step etching and tapering enhances the strength and penetration depth of the evanescent wave significantly.     

Painlev Analysis,Lie Symmetries and Exact Solutions for Variable Coefficients Benjamin-Bona-Mahony-Burger (BBMB) Equation

In this paper,a variable-coefficient Benjamin-Bona-Mahony-Burger (BBMB) equation arising as a mathematical model of propagation of small-amplitude long waves in nonlinear dispersive media is investigated.The integrability of such an equation is studied with Painlev analysis.The Lie symmetry method is performed for the BBMB equation and then similarity reductions and exact solutions are obtained based on the optimal system method.Furthermore different types of solitary,periodic and kink waves can be seen with the change of variable coefficients.     

Spin-polarized two-dimensional electron gas at oxide interfaces

The possibility of formation of a fully spin-polarized 2D electron gas at the SrMnO_3/(LaMnO_3)_1/SrMnO_3 heterostructure is predicted from density-functional calculations. The La(d) electrons become confined in the direction normal to the interface in the electrostatic potential well of the positively charged layer of La atoms, acting as electron donors. These electrons mediate a ferromagnetic alignment of the Mn t_2g spins near the interface via Zener double exchange and become, in turn, spin-polarized due to the internal magnetic fields of the Mn moments.     

Volume Bragg grating stabilized spectrally narrow Tm fiber laser

A Tm-doped large mode area (LMA) silica fiber laser has been locked to a stable wavelength of 2,053.9 nm using a volume Bragg grating (VBG). The measured spectral width of the laser output was <300 pm, limited by the spectrometer resolution. Although this laser had modest output (approximately 5W) and slope efficiency (41%), this new approach to spectrally limiting the output of LMA fiber lasers is inherently extendable to kilowatt powers, opening up several applications including high-power pulsed fiber lasers and spectral beam combining. Performance characteristics of the laser compared to one using a dielectric mirror as a high reflector are described, and the results imply low VBG losses.     

Thermodynamic model for the size-dependent melting of prism-shaped nanoparticles

We report on the size-dependent melting of prism-shaped nanoparticles based on thermodynamic model and applied to understand the melting of prism-shaped indium nanoparticles. It is shown here that the bulk melting temperature cannot be extrapolated from the nanoscale and the extrapolated value will always be lower than the bulk melting temperature as has been observed experimentally.     

A Catalyst and Solvent Free Route for the Synthesis of N-Substituted Pyrrolidones from Levulinic Acid

An efficient, metal-free, catalyst-free and solvent-free methodology for the reductive amination of levulinic acid with different anilines has been developed using HBpin as the reducing reagent. This protocol offers an excellent method to avoid solvents and added catalysts on the synthesis of different kinds of N-substituted pyrrolidones under metal free conditions. It is also the first report for the synthesis of different pyrrolidones by solvent-free as well as catalyst-free methods. The proposed mechanism for the formation of pyrrolidone has been supported by DFT calculations and control experiments.     

Ionic Assembly,Anion–π, Magnetic,and Electronic Attributes of Ambient Stable Naphthalenediimide Radical Ions

Organic spin-based molecular materials are considered to be attractive for the generation of functional materials with emergent optoelectronic, magnetic, or magneto-conductive properties. However, the major limitations to the utilization of organic spin-based systems are their high reactivity, instability, and propensity for dimerization. Herein, we report the synthesis, characterization, and magnetic and electronic studies of three ambient stable radical ions ( 1 a^.+ , 1 b^.+ , and 1 c^.+ ). The radical ions 1 b^.+ and 1 c^.+ with BPh₄⁻ and BF₄⁻ counter anions, respectively, were synthesized in excellent yields by means of anion metathesis of 1 a^.+ with Br⁻ as its counter anion. Notably, synthesis of 1 a^.+ was achieved in an ecofriendly, solvent-free protocol. The radical ions were characterized by means of single-crystal X-ray diffraction studies, which revealed the discrete nature of the radical ions and extensive hydrogen-bonding interactions within the radical ions and with the counter anions. Thus, radical ions can be organized to form infinite supramolecular arrays using weak noncovalent interactions. In addition, the Br⁻, BF₄⁻, and BPh₄⁻ anions formed diverse types of anion–π interactions with the naphthalene and imide rings of the radical ions. The radical ions were characterized by means of X-band electron paramagnetic resonance (EPR) spectroscopy in solution and in the solid state. Magnetic studies revealed their paramagnetic nature in the range of 10 to 300 K. The radical ions exhibited high resistivity approaching the gigaohm (GΩ) scale. In addition, the radical ions exhibited panchromism.