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- W2334671572 abstract "Sulfur-based heteroaromatic cores oftenimpart advantageous properties to liquid crystals (LCs). Onelittle-investigated sulfur-based heterocyclic family isthienothiophene; recently, thienothiophene-based materials haveattracted exponentially growing attention in a variety of materialsapplications. However, thienothiophenes have largely escaped thenotice of the LC community. In this thesis, we present an initialexploration into the effect of the thienothiophene core on themesomorphic properties of LCs. Thus, we have synthesized severalfamilies of target LCs: alkyl5-(4-alkoxyphenyl)thieno[3,2- b ]thiophene-2-carboxylateesters ( I ), alkyl5-(4-alkoxyphenyl)thieno[2,3- b ]thiophene-2-carboxylateesters ( II ), and two alkoxythienothiophene-basedLCs (4-(alkoxycarbonyl)phenyl5-(alkoxy)thieno[3,2- b ]thiophene-2-carboxylate( III ) and 4-(alkoxy)phenyl5-(alkoxy)thieno[3,2- b ]thiophene-2-carboxylate( IV )). In the synthesis of I , we elaborated a series of alkyl2-mercaptoacetates to alkylthieno[3,2- b ]thiophene esters in an efficientand operationally facile tandem nucleophilic substitution and aldolreaction. These thienothiophene esters were regioselectivelyhalogenated at the a-position and submitted to Pd(0)-catalyzedSuzuki-Miyaura cross-coupling with a series of potassium4-alkoxyphenyltrifluoroborate salts to yield the target LCs. Thissynthesis was efficient and marks the first use of thetrifluoroborate variant of Suzuki-Miyaura coupling in the LC field.Family II was prepared in an analogousmanner. For the synthesis of III and IV we developed astrategically novel and facile route to 2-alkoxythiophenes by mildoxidation and Mitsunobu etherification of a series of easilyprepared thiophen-2-yltrifluoroborate salts. With these materialsin hand, 4-bromo-2-octyloxythiophene was regioselectivelyformylated by LDA-mediated deprotonation and attack by N -formylpiperidine. The resulting3-bromo-5-octyloxythiophene-2-carbaldehyde was submitted to similarring-closing conditions with a mercaptoacetate as in I and II to yield the firstlong-chain 2-alkoxythieno[3,2- b ]thiophene. Thisester was then hydrolyzed and submitted to Steglich esterificationto give targets III and IV . Mostthieno[3,2- b ]- and[2,3- b ]thiophene-based materials presented inthis study were found to exhibit the smectic C (SmC) mesophase.Notably, thienothiophene-based materials gave rise to much widermesophases than their phenyl analogues. We found thatthieno[2,3- b ]thiophene, while less oftenexploited in the design of materials, gave markedly wider SmCmesophases in LCs than theirthieno[3,2- b ]thiophene analogues. When weincorporated a chiral tail into these molecules, however, theinfluence of the core on LC properties was destroyed and nosignificant difference was seen betweenthieno[2,3- b ]- andthieno[3,2- b ]thiophene-based LCs.…" @default.
- W2334671572 created "2016-06-24" @default.
- W2334671572 creator A5048565997 @default.
- W2334671572 date "2012-01-01" @default.
- W2334671572 modified "2023-09-26" @default.
- W2334671572 title "Thienothiophene-Based Liquid Crystals: Synthesis and Comparative Evaluation of Mesophase Properties" @default.
- W2334671572 hasPublicationYear "2012" @default.
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