ABSTRACT
Dual catalysis has become a desirable alternative because of the synergetic effect of two distinct catalysts, but little is known about the mechanism of dual catalysis and its effect on the high reactivity and selectivity. Here, a novel Ullmann C-C cross-coupling of bromobenzene and 4-methoxyphenyltriflate via nickel/palladium dual catalysis has been investigated using density functional theory. The orthogonal reactivity of NiI/Pd0 combination is the precondition and foundation of achieving such a Ullmann cross-coupling reaction. In the present dual catalysis, the NiI complex acts as the primary catalyst, while the Pd0 catalyst plays a decisive role in the cross-selectivity.
ABSTRACT
The lasing spectrum of dye-doped chiral nematic liquid crystal under electric filed was investigated. Two kinds of electrodes were designed to apply transverse electric field to positive liquid crystal cell and longitudinal electric field to negative liquid crystal cell. A 532 nm Ndâ¶YAG pulsed solid-state laser was used to pump the cell. When transverse electric field is applied to positive liquid crystal device, multi-wavelength laser output is obtained in the range of 630~660 nm. When longitudinal electric field is applied to negative liquid crystal cell, 18.5 nm tunable output lasing is obtained. The output characteristic of cell was analyzed from the texture of device and the photonic band gap. In the positive liquid crystal cell, the competition of electric moment with twisting moment causes the flow of LC molecule, and the flow of LC molecule leads to a floating photonic band gap. For this reason, not only at the edge of photonic band gap but in the photonic band gap can produce lasing. For negative liquid crystal cell, the pitch shrinks with the increase of electric field. The photonic band gap shows blue-shift with the decrease of pitch. and Lasing wavelength is blue shifted from 681.0 to 662.5 nm and the lasing at the edge of photonic band gap. Negative liquid crystal cell has better stability under electric field effect.
ABSTRACT
2, 2, 3, 3, 4, 4-hexafluoro-1,5-pentanediol dicinnamate ester, which could be crosslinked under irradiation of linearly polarized ultraviolet light, was synthesized in the present work. UV-Visible spectra and FTIR spectra revealed that [2+2] cycloaddition was the main reaction of the monomer, but there was no clear morphological anisotropy on the surface of the obtained photoalignment film through atomic force microscopic analysis. The photoalignment film could induce homogenous alignment of liquid crystal and the alignment is uniform. It was found that the pretilt angle of the photoalignment film is 1 degrees-2 degrees.
