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2H NMR studies of phase behaviour and molecular motions of doped discotic liquid-crystalline systems

 

作者: Wolfgang Kranig,   Christine Boeffel,   HansWolfgang Spiess,   Olaf Karthaus,   Helmut Ringsdorf,   Renate Wüstefeld,  

 

期刊: Liquid Crystals  (Taylor Available online 1990)
卷期: Volume 8, issue 3  

页码: 375-388

 

ISSN:0267-8292

 

年代: 1990

 

DOI:10.1080/02678299008047354

 

出版商: Taylor & Francis Group

 

数据来源: Taylor

 

摘要:

A discotic triphenylene monomer as well as a dimer and a main chain polymer, all substituted with heptyloxy side groups, were doped with an electron acceptor (2,4,7-trinitrofluorenone (TNF)) to give charge transfer complexes. These doped systems were aligned in a magnetic field, thus proving their liquid crystallinity.2H NMR measurements show that the electron acceptor molecules are incorporated into the columns built of triphenylene cores. In the charge transfer complex with the triphenylene monomer almost all the electron acceptor molecules stack in the columns even close to the clearing temperatureT1, while for the dimer and especially for the polymer a significant fraction of the TNF molecules exhibits isotropic motion, which is attributed to their location in the region between the columns, already way belowT1. This isotropically distributed part increases on approachingT1. Fast rotation of the discs around their column axes takes place in the monomer and is quenched in the dimer and the polymer, due to the interlinking of the columns by the spacer. The electron acceptor molecules, on the other hand, exhibit free rotation in all samples, even in the charge transfer complexes with the triphenylene dimer and polymer. In the side group labelled triphenylenes increased2H NMR spectral narrowing is detected in the charge transfer complex samples compared with the corresponding pure triphenylenes. This indicates higher side group mobility in the doped systems, since the incorporation of TNF molecules increases the spacing between the discotic units.

 

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