An optical, electro-optic and thermal characterisation of various organic crystals

The organic materials S - 3 - methyl - 5 - nitro - N - (1 - phenylethyl) - 2 - pyridinamine [3- methyl-MBANP] and S - N - methyl - 5 - nitro - N -(1 - phenylethyl) - 2 - pyridinamine [N- methyl-MBANP] belong to a family of compounds based on the 2-(alpha-methylbenzylamino)-5- nitropyridine molecule and were identified as promising nonlinear optical materials by the powder disk test. Large single crystals were grown from solution for N-methyl-MBANP, which crystallises in a monoclinic space group, and from the melt and solution for 3-methyl-MBANP which crystallises in an orthorhombic space group. Orthoscopic examination of N-methyl-MBANP revealed no dispersion of the dielectric axes unlike the parent molecule and the position of the dielectric axes was correlated with the molecular structure. Preparation of prisms from single crystals of both materials facilitated the measurement of refractive indices in the visible and the near infra-red. The values obtained were correlated with the crystal structure and a Sellmeier equation fitted to each of the dispersion curves. The nonlinear optical properties of both materials were evaluated by use of the Maker fringe technique and phase matched intensities. By means of these two methods, the full nonlinear d sub i sub j tensor was obtained for both materials at a fundamental wavelength of 1064nm. The linear electro-optic properties of N-methyl-MBANP were evaluated using a conoscopic experiment and correlated with the crystal structure together with the magnitude of all non-zero elements in the d sub i sub j tensor. Separately, the thermal properties of N-methylurea (NMU), 4-nitro-4'-methylbenzylidene aniline (NMBA) and Zinc TrisThiourea Sulfate (ZTS) were evaluated and all correlated with the crystal structure and bonding

The nonlinear optical properties of the crystal (S)-3-methyl-5-nitro-N-(1-phenylethyl)-2-pyridinamine

The organic crystal (S)-3-methyl-5-nitro-N-(1 -phenylethyl)-2-pyridinamine has been previously identified by the powder technique as a promising nonlinear optical material. Large single crystals (3 x 3 x 2 cm(3)) of this material have been grown by temperature lowering of a seeded supersaturated solution in acetone, Refined refractive indices were obtained from the predicted angles of incidence of the phase-matched second harmonic signals. Second-order nonlinear optical coefficients, d(ij), as measured by the Maker fringe technique, are 11, 9, and 7 pm V-1 for d(14), d(25), and d(36). respectively. The results are compared with calculations based on the oriented gas model

Synthesis, characterisation and structure-property analysis of derivatives of the non-linear optical material 5-nitro-N-(1- phenylethyl)pyridin-2-amine

The effects of a series of small structural changes to (S)-5-nitro-N-(1-phenylethyl)pyridin-2-amine on its solid state non-linear optical properties, including the phenomenon of rotating dielectric axes, have been investigated. Installation of a methyl group in the 3-position of the heterocyclic ring or at the amino nitrogen atom gave the most promising materials, though neither of these materials showed rotating dielectric axes. Details of the crystal structure analyses of a family of these compounds illustrate the delicate interplay between molecular conformation and intermolecular interactions in determining the packing arrangements

Refractive indices of the optically nonlinear organic crystal (S)-3-methyl-5-nitro-N-(1-phenylethyl)-2-pyridinamine

The refractive indices of structurally well-characterized crystals of the new optically nonlinear organic crystal (S)-3-methyl-5-nitro-N-( I-phenylethyl)-2-pyridinamine have been measured from 480 to 660 nm and fitted to four-parameter Sellmeier equations with an accuracy of +/-3 x 10(-3) to +/-5 x 10(-3). The value of n(y) was accurately verified by the measurement of the external angle of incidence required, at the (101) plane, to observe type I phase matching with a fundamental wavelength of 1064 nm. The phase matching locus has been established and is of Hobden class eight. The values of the n(x), n(y), and n(z) refractive indices at 532 nm were found from the Sellmeier equations to be 1.690, 1.901, and 1.725, respectively, and their relative magnitudes are correlated with the molecular arrangement in the crystal lattice. This material is a member of a series of pyridinamines that can exhibit the phenomenon of frequency-dependent orientation of their dielectric axes. Since this compound crystallizes in an orthorhombic structure, rotation of the dielectric axes is precluded for symmetry reasons

Thermal properties of the nonlinear optical crystal zinc tris (thiourea) sulphate

The heat capacity of crystalline zinc tris (thiourea) sulphate, has been measured in the range from 220 to 500 K by differential scanning calorimetry, and was found to obey the relationship Cp(T)=2.76×10−3 T+0.366 J g−1 K−1. Thermal expansion data have been measured in the range from 150 to 473 K. From these data, the principal thermal expansion coefficients were found to be α1=6.41×10−5 K−1, α2=4.52×10−5 K−1, and α3=−4.32×10−6 K−1. The thermal conductivity tensor of this orthorhombic crystal was calculated from values of the thermal diffusivity in the directions normal to the (100), (010), and (001) crystal planes by the laser flash method. The thermal conductivity coefficients at 295 K are k=0.27 W m−1 K−1, k2=0.34 W m−1 K−1, and k=0.54 W m−1 K−1. REFERENCE

Linear and nonlinear optical properties of organic crystals: MBANP and its derivatives

In addition to possessing strong optical nonlinearity, the (-)-2-(alpha-methylbenzylamino)-5-nitropyridine (MBANP) crystal has been shown to have unusual linear optical properties. Two methyl derivatives of MBANP have now been synthesized and grown as large single crystals; their refractive indices have been measured as a function of frequency and second-harmonic generation, including the determination of the phase matching loci has been investigated. Data is also available on the racemic form of crystalline MBANP. The properties of this family of crystals have been reviewed and an attempt is made to relate the experimental responses of the crystals to their molecular structure and the calculated properties of the molecules

Moving beyond the conceptual: specificity in regional climate change adaptation actions for biodiversity in South East Queensland, Australia

While many scientific assessments have been recommending general strategies for biodiversity conservation under climate change, translation of these recommendations into specific actions and practice has been limited. Focusing on two biomes, rainforest and wetlands in biodiverse South East Queensland, Australia, we demonstrate how general principles can be translated into specific actions for stakeholders and responsible agencies. We synthesize research that is contextualizing protection of refugia and habitat connectivity, establishing baseline data sets to detect change and developing strategic conservation planning scenarios to adjust reserve boundaries or situate new reserves. This has been achieved by coupling spatial information on biological assets (i.e. ecosystems and species) with future climate scenarios and process models to anticipate movement of critical habitats. Conservation planning software is also being used to prioritize investment to meet specific objectives. This approach is enabling us to identify at-risk biological assets, opportunities to ameliorate threats and obstacles to delivering regional adaptation actions. A larger total reserved area is needed, with proactive planning to capture areas further inland and along watercourses. Major obstacles include conflict between urbanization and priorities for habitat conservation and the need for greater levels of investment for monitoring programmes and to protect landward shifted wetlands on private lan