Liquid crystalline organic semiconductors for application in opto-electronic devices

Billa, Muralidhar Reddy

March 2015

Thesis or dissertation

© 2015 Muralidhar Reddy Billa. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.

The synthesis and evaluation of novel photo-reactive liquid crystalline materials that exhibit light emitting, charge transporting and photovoltaic properties is described. Low-molar-mass liquid crystalline monomers, based on a series of substituted thiophenes, thieno[3,2-b]thiophenes, benzo[1,2-b:4,5-b']dithiophene, 4,7-dibromobenzo- 1,2,5-thiadiazole, fluorenes and carbazoles have been synthesised. Most of the materials synthesised incorporate two 9-octyl carbazole end groups at 3 positions. Some of the materials synthesised incorporate methacrylate end groups attached to the peripheries of the molecule at the end of flexible aliphatic chains. Polymerisation of these end groups allows the production of multilayer OLEDs with a very small pixel size due to the insoluble cross-linked network obtained after photo-polymerisation. The creation and analysis of novel multi-layer OLEDs with exceptionally small pixal size was possible by the incorporation of photo-polymerizable group into the liquid crystalline compounds.

The molecular core incorporates either a 9-octyl carbazole end groups at the two ends of a fluorene moiety or an N-alkyl-substituted carbazole in the centre of the molecule. The presence of these two new types of liquid crystalline monomers for use as polymer networks in OLEDs should lead to higher electrochemical stability towards oxidation and thereby give rise to longer life-times in OLEDs containing them.

Exceptinally, several of these novel OLED materials exhibit blue photoluminescence and electroluminescence, enabling their incorporation into multicolour OLEDs. This thesis details the synthesis of two different types of molecular central moieties, i.e., fluorene and carbazole with photopolymerisable end groups or 9-octyl carbazole end groups for implementation as initiators in multilayer organic devices. The photo reactive end groups are based on the acrylate moieties.

Department of Chemistry, The University of Hull
Kelly, S. M. (Stephen Malcolm); Hird, Michael
Qualification level
Qualification name
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