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Longer Spacers (longer + spacer)
Selected AbstractsInfluence of Side-Chain Structure and Irradiation Condition on Photoalignment of Ladder-Like Polysiloxane Films,ADVANCED FUNCTIONAL MATERIALS, Issue 1 2005H.-W. Gu Abstract In this paper we consider the photo-induced aligning capability of various ladder-like polysiloxane-based photoalignment films,which could be used in liquid-crystal displays,bearing different photoreactive side chains, i.e., laterally grafted cinnamate/azobenzene-based dual photoreactive side chains with a short or longer spacer, and terminally fixed coumarin-containing side chains. Results from polarized optical microscopy (POM), Fourier-transform infrared (FTIR) spectroscopy, surface-enhanced Raman scattering (SERS), atomic force microscopy (AFM), etc., are integrated to elucidate the influence of side-chain structure and the irradiation conditions on the photoalignment of ladder-like polysiloxane films. It is demonstrated that the film containing the dual photoreactive group with a longer spacer exhibits better alignment properties. Reasonably, the concerted photoreactions of the dual photoreactive group and the longer spacer are beneficial to the cooperative motion of chromophores at the "domain level", resulting in improved alignment facility and stability. The complicated effects of irradiation conditions and moderate annealing are also discussed. High-quality alignment of the polysilsesquioxane (LPS)-based photoalignment film LPS-CA11 with a longer spacer between the LPS main chain and cinnamoyl/azobenzene side chains can be achieved only within an optimal range of exposure (5,8,J,cm,2), while the pretilt angles can be adjusted in the range 0.5°,7° by varying the incident light intensity. Additionally, moderate annealing before and after illumination can markedly improve the alignment uniformity by self-healing of defects. [source] Studies on the modification of poly(,-bromoalkyl-1-glycidylether)s with 4,-methoxybiphenyl-4-oxy mesogenic groupsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2005J. M. Montornés Abstract A series of poly[,-(4,-methoxy-biphenyl-4-oxy)alkyl-1-glycidylether]s were synthesized by chemically modifying the corresponding poly(,-bromoalkyl-1-glycidylether)s with the sodium salt of 4-hydroxy-4,-methoxybiphenyl. New high-molecular-weight side-chain liquid-crystalline polymers were obtained with excellent yields and almost quantitative degrees of modification. They were all insoluble in THF and other common solvents. Characterization by 13C NMR confirmed that all the polymers had the expected structure. The liquid crystalline behavior of the polymers was analyzed by DSC and polarized optical microscopy, and mesophase assignments were confirmed by X-ray diffraction studies. Polymers that had alkyl spacers with n = 2 and 4 were smectic C, those that had spacers with n = 6 and 8 were nematic cybotactic, and those that had longer spacers (n = 10 and 12) were smectic C again. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5998,6006, 2005 [source] Photoluminescent behavior of poly(3-hexylthiophene) derivatives with a high azobenzene content in the side chainsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 5 2005Xiongyan Zhao Abstract A series of polythiophene derivatives with substantially higher azobenzene contents in the side chains were prepared via copolymerization of 3-hexylthiophene with four different types of 4-((4-(phenyl)azo)phenoxy)alkyl-3-thienylacetate. The alkyl spacers with different lengths, i.e. butyl, hexyl, octyl and undecyl groups were used between the azobenzene group and the thiophene ring. The compositions, structures and thermal properties of these polythiophene derivatives were characterized. The structural dependence of photoluminescent emission, photochromic behavior of these copolymers were systematically studied and compared with poly(3-hexylthiophene). The results show that the azobenzene substitution renders the polythiophene some interesting optical properties that can be modulated by UV light irradiation. In the azobenzene modified polythiophene, the intensity of photoluminescent emission associated with the conjugated polythiophene main chain was found to decrease significantly upon UV irradiation. The finding suggests that the photo-induced trans - cis isomerization of the azobenzene pendant groups has a significant effect on photoluminescent emission, particularly when short spacers are used between azobenzene groups and the main chain. However, the effect becomes less prominent when longer spacers are used between the azobenzene group and the main chain. Furthermore, UV irradiation of the copolymers also resulted in an increase in intensity and broadening of bandwidth for the absorption peak associated with the polythiophene backbones. Again the magnitude of intensity changes upon UV irradiation were found to be dependent on the spacer length between the azobenzene group and polythiophene main chain. Copyright © 2005 John Wiley & Sons, Ltd. [source] Modifying the structure of dinuclear ruthenium complexes with antitumor activityAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 6 2008Maria G. Mendoza-Ferri Abstract In order to modulate the structure of a recently developed series of antitumor-active, dinuclear Ru(II),arene compounds, complexes 1c,4c were synthesized. The complexes were modified with respect to their pyridinone moieties and the spacer linking the two metal centers. More particularly, the series of dinuclear ruthenium(II) complexes was extended to compounds with longer spacers, i.e. tetradecane and 3,7,10-trioxotridecane, and the pyridinone ring was modified by replacing the methyl group by an ethyl group and by shifting the position of the methyl group. The organometallic ruthenium compounds were obtained from the reaction between [RuCl2(,6 - p -isopropyltoluene)]2 and ligands 1b,4b with yields ranging from 41 to 67%. All compounds were characterized by standard methods: MS, 1H and 13C NMR spectroscopy and elemental analysis. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||