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Title: Synthesis and characterisation of substituted dithienothiophene derivatives for field-effect transistors
Author: Armitage, M. A.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2007
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Some of the best-performing organic field-effect transistors (OFETs) use thiophene-based semiconductors such as poly(3-hexylthiophene) (P3HT) and poly(9,9-dioctylfluorene-alt­-bithiophene) (F8T2). In recent years much interest has been directed to dithieno[3,2-b:2’,3’-d]thiophene (DTT) as a unit in semiconducting organic materials. However, these derivatives were also largely insoluble. Because insoluble organic materials do not present a practical alternative to widely-used inorganic semiconductors like silicon, there is a lot of interest in creating organic semiconductors that can be processed from solution. Hence, this thesis is focused on the preparation of soluble DTTs as semiconductors for OFETs. As DTT is relatively unreactive, the best approach to soluble derivatives is shown to be to incorporate solubilising groups as the DTT skeleton is built. The synthetic route applied, based on Friedel-Crafts acylations followed by annelations with ethyl 2-mercaptoacetate, allows the formation of a wide range of 3- and 3,5-substituted DTTs. The route is also flexible in that the 3,5-disubstitued DTTs may be symmetric or asymmetric. The synthetic method also features a one-pot conversion of substituted DTT-2,6-diesters into 2,6-dibromoDTTs, which can then be reacted under palladium-catalysed cross-coupling conditions to form new conjugated macromolecules and polymers. This bromo-decarboxylation process improves on the classical route by removing the need for toxic quinoline in the decarboxylation of DTT-2,6-dicarboxylic acids. The new substituted DTT derivatives were incorporated into soluble conjugated homo- and copolymers. Some of the new polymers were good hole-transporters, with mobilities up to 10-4 cm2 V-1 s-1 being measured in OFETs. This value is only one order of magnitude lower than has been reported for commercial F8T2, showing that these materials have good potential for optoelectronic applications.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available