Thiophene-based photoresponsive mesogens

Chambers-Asman, D (2007)
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This thesis reports the synthesis, transition temperatures and structure-property relationships of a variety of thiophene-containing azobenzene esters derived from either 3-(2-thienyl)acrylic acid (Series I, IV, VI, VIII, X and XII) or 3-(3-thienyl)acrylic acid (Series II, V, VII, IX, XI and XIII) and appropriate fluoro- and non-fluoro-substituted 'azophenols', for potential use in photoresponsive applications. For comparative purposes, the non-heterocyclic cinnamate counterparts (Series III) were also prepared and are reported. All one hundred and thirty final esters are mesomorphic, exhibiting the nematic phase alone. The mesomorphic properties are dependent upon the disposition of the terminal thiophene moiety. In general 3-thienyl-substitution gives thermally more stable compounds than 2-thienyl-substitution. Influence of mono- (Series IV, V, VI and VII) and di- (Series VIII, IX, X, XI, XII and XIII) lateral fluoro-substitution on mesomorphic properties is investigated in detail Lateral fluorination lowers mesophase thermal stability and its extent is dependent upon the number and disposition of the lateral fluoro-substituents. Di-lateral fluorination across the long molecular axis is more detrimental to mesophase thermal stability than along the long molecular axis. UV-Vis steady state photoresponsive studies on Series I show that trans-cis photoisomerisation may be induced at 367 nm, with the reverse cis-trans isomerisation process occurring 434 nm.

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