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1998, No. 13
Show moreMagnetic and electrical Freedericksz measurements were performed on the second generation monodendritic liquid crystal G2(OH). The deduced elastic constants were found to be exceptionally anisotropic: the splay elastic constant K11 is more than an order of magnitude larger than the bend elastic constant K33, and the twist constant K22 is approximately twice K33. The results are discussed in terms of molecular conformations. European Physical Journal B 5 1998 pp. 251-255 Highly anisotropic elasticity of a dendrimeric liquid crystal Petschek R.G. With kind permission of The European Physical Journal (EPJ).
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Show moreWe have designed a hyper-Rayleigh scattering scheme to measure six scalar invariants of the squared hyperpolarizability tensor β2. Our theoretical approach expresses the rotational invariants of the irreducible β components as scalars, which eliminates the need for difficult frame transformations. We applied our scheme to several conjugated chiral molecules and found that there are significant Kleinmann-disallowed pseudotensor contributions to their hyperpolarizability. These components, along with a large optical rotation and the results of quantum-chemical calculations, indicate a handed nonplanar delocalization of the charge-transfer system in such molecules as predicted by quantum-chemical calculations and are expected to lead to macroscopic second-harmonic generation in axially aligned polymer materials. Pseudotensor contributions to the hyperpolarizability in chiral molecules were found to be as large as the vector contribution in p-nitroaniline. We qualitatively investigated the dispersion in the Kleinmann-disallowed components and confirmed that these components are smaller at longer wavelengths. © 1998 Optical Society of America.
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Show moreA tunable source is used to study the competition between hyper-Rayleigh scattering (HRS) and multi-photon fluorescence in the detected signal near the second-harmonic by examining the spectral content of the scattered light and its dispersion in the infrared. It is found that even at frequencies noticeably lower than half that of the linear absorption, there is a rapid decrease in the HRS peak and rapid increase in two photon fluorescence. This is attributed to dephasing of the virtual excited state. This transition occurs far from the resonance peak. Two compounds, p-nitroaniline and disperse red 1, are studied, showing that accurate internal referencing can be carried out by considering the symmetry of the solvent to yield accurate measurements of the first hyperpolarizability.
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1998, No. 13
Show moreMagnetically induced Freedericksz measurements were performed in the nematic liquid crystal phase to extract the elastic constants of a terminal-lateral-lateral-terminal trimer, i.e., a trimer in which the connections to the first and third mesogens are at the end of the mesogen and both attachments to the central mesogen are lateral. Polymeric liquid crystals based on this unit have negative Poisson ratios. Additionally, electric field Kerr measurements were performed in the isotropic phase to extract the orientational susceptibility. The elastic constants were found to be similar to values obtained for typical monomers, albeit with a slightly enhanced ratio K33/K11 and reduced ratio K11/K22, especially near the transition temperature. The temperature dependence of the susceptibility was found to deviate significantly from that of typical monomers. The observed behavior is discussed in terms of coupled order parameters representing the terminal and core mesogens of the molecule. Appropriate bibliographic citation and notice of the APS copyright must be included- "Kang D., Mahajan M.P., Petschek R.G., Rosenblatt C., He C., Liu P., Griffin A.C., Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics 58:2 SUPPL. B, 2041-2046 (1998). Copyright 1998 by the American Physical Society."
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1998, No. 13