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Thiruvananthapuram, India

Redwood C.,Florida State University | Kumar V.K.R.,Florida State University | Kumar V.K.R.,VTM NSS College | Hutchinson S.,Florida State University | And 4 more authors.
Journal of Physical Chemistry A | Year: 2014

The vibronic structure of the fluorescence spectrum of trans-1,2-di(1-methyl-2-naphthyl)ethene (t-1,1) in methylcyclohexane (MCH) solution at room temperature was expected to become better defined upon cooling of the solution to 77 K. Instead, a broad, λexc-dependent fluorescence spectrum was observed in the glassy medium. Vibronically structured t-1,1 fluorescence spectra were obtained in the MCH glass only upon irradiation at the long-λ onset of the absorption spectrum. The application of singular value decomposition with self-modeling on the fluorescence spectral matrices of t-1,1 allowed their resolution into major and minor pairs of vibronically structured spectra that are assigned to two structural modifications of each of two relative orientations of the 1-methyl-2-naphthyl moieties. The difference between the two structures in each pair lies in the direction of rotation of each naphthyl group away from the plane of the olefinic bond. A complex but different conformer distribution is also responsible for the fluorescence spectra of t-1,1 in 5:5:2 (v/v/v) diethyl ether/isopentane/ethyl alcohol (EPA) glass at 77 K. The conformer distributions are also sensitive to the rate of cooling used in glass formation. Conformer distributions based on predicted small energy differences from gas-phase theoretical calculations are of little value when applied to volume-constraining media. The photophysical and photochemical properties of the analogues of the other two conformers of trans-1,2-di(2-naphthyl)ethene, trans-1-(1-methyl-2-naphthyl)-2-(3-methyl-2-naphthyl)ethene (t-1,3) and trans-1,2-di(3-methyl-2-naphthyl)ethene (t-3,3), were determined in solution. However, it is the calculated geometries and energy differences of the t-1,1 conformers [DFT using B3LYP/6-311+G(d,p)] that are essential guides to the interpretation of the experimental results. © 2014 American Chemical Society. Source

Sujith A.,National Institute of Technology Calicut | Shebi A.,National Institute of Technology Calicut | Sudheesh P.,VTM NSS College | Kumar M.S.,National Institute of Technology Calicut | Chandrasekharan K.,National Institute of Technology Calicut
Micro and Nano Letters | Year: 2014

Poly(methyl methacrylate) (PMMA) microparticles doped with natural dyes such as paprika and chlorophyll have been prepared by the solvent evaporation technique. A mixture of paprika and chlorophyll in different ratios was also doped with microparticles. The distribution of the diameter of particles spreads in the range of 3-7 μm. UV-visible spectroscopic studies have shown that the absorption wavelength is shifted to a longer wavelength region when the paprika content increases in the dopant mixture. The nonlinear optical properties of the samples were investigated. It is found that the coloured particles have remarkable optical nonlinearities in the nanosecond regime because of the interaction of double bonds in PMMA with the delocalised π-electron system of dyes. © The Institution of Engineering and Technology 2014. Source

Redwood C.,Florida State University | Ratheesh Kumar V.K.,Florida State University | Hutchinson S.,Florida State University | Mallory F.B.,Bryn Mawr College | And 5 more authors.
Photochemistry and Photobiology | Year: 2015

Abstract cis-1,2-Di(1-methyl-2-naphthyl)ethene, c-1,1, undergoes photoisomerization in methylcyclohexane, isopentane and diethyl ether/isopentane/ethanol glasses at 77 K. On 313 nm excitation the fluorescence of c-1,1 is replaced by fluorescence from t-1,1. Singular value decomposition reveals that the spectral matrices behave as two component systems suggesting conversion of a stable c-1,1 conformer to a stable t-1,1 conformer. However, the fluorescence spectra are λexc dependent. Analysis of global spectral matrices shows that c-1,1 is a mixture of two conformers, each of which gives one of four known t-1,1 conformers. The λexc dependence of the c-1,1 fluorescence spectrum is barely discernible. Structure assignments to the resolved fluorescence spectra are based on the principle of least motion and on calculated geometries, energy differences and spectra of the conformers. The relative shift of the c-1,1 conformer spectra is consistent with the shift of the calculated absorption spectra. The calculated structure of the most stable conformer of c-1,1 agrees well with the X-ray crystal structure. Due to large deviations of the naphthyl groups from the ethenic plane in the conformers of both c- and t-1,1 isomers, minimal motion of these bulky substituents accomplishes cis → trans interconversion by rotation about the central bond. One bond twist photoisomerization of cis-I,2-di(1-methyl-2-naphthyl)ethene in glassy media. © 2014 The American Society of Photobiology. Source

Nair R.M.,Mahatma Gandhi College | Sudarsanakumar M.R.,Mahatma Gandhi College | Sudarsanakumar M.R.,VTM NSS College | Suma S.,S N College | And 2 more authors.
Inorganic Chemistry Communications | Year: 2016

Single crystals of a novel 1D coordination polymer, [Ca9(μ-H2O)9(picolinate)18]·4H2O were grown by single gel diffusion technique. Sodium metasilicate was used for gel preparation. Single crystal X-ray diffraction studies reveal that the compound crystallizes in triclinic space group Pi¯. The crystal possesses a large asymmetric unit with bridging picolinate ligands and water molecules. The 1D chain like structure constructs a 2D supramolecular architecture via the hydrogen bonding interactions. The grown crystals were further characterized by elemental analysis, powder X-ray diffraction study, FT-IR and UV-Visible spectral studies. The luminescent behaviour of the ligand and the complex was also investigated. © 2015 Elsevier B.V. Source

Yuan Z.,Florida State University | Tang Q.,University of California at Riverside | Sreenath K.,Florida State University | Sreenath K.,VTM NSS College | And 5 more authors.
Photochemistry and Photobiology | Year: 2015

Abstract 2-(2′-Hydroxyphenyl)benzoxazole (HBO) is known for undergoing intramolecular proton transfer in the excited state to result in the emission of its tautomer. A minor long-wavelength absorption band in the range 370-420 nm has been reported in highly polar solvents such as dimethylsulfoxide (DMSO). However, the nature of this species has not been entirely clarified. In this work, we provide evidence that this long-wavelength absorption band might have been caused by base or metal salt impurities that are introduced into the spectral sample during solvent transport using glass Pasteur pipettes. The contamination by base or metal salt could be avoided by using borosilicate glass syringes or nonglass pipettes in sample handling. Quantum chemical calculations conclude that solvent-mediated deprotonation is too energetically costly to occur without the aid of a base of an adequate strength. In the presence of such a base, the deprotonation of HBO and its effect on emission are investigated in dichloromethane and DMSO, the latter of which facilitates deprotonation much more readily than the former. Finally, the absorption and emission spectra of HBO in 13 solvents are reported, from which it is concluded that ESIPT is hindered in polar solvents that are also strong hydrogen bond acceptors. Minor long-wavelength absorption bands of the excited state intramolecular proton transfer (ESIPT) dye 2-(2′-hydroxyphenyl)benzoxazole (HBO) have been observed in DMSO by us and others. These bands might have been caused by base or metal salt impurities introduced by glass Pasteur pipettes that are equipped with latex rubber bulbs. Without the interference of extraneous bases or metal salts, solvent-mediated deprotonation fails to occur. The propensity of HBO to deprotonation is much higher in DMSO than in less polar solvents. The solvatochromic shifts of HBO suggest that the ESIPT is hindered in polar solvents that are also strong hydrogen bond acceptors. © 2014 The American Society of Photobiology. Source

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