One challenge in the development of ferroelectric liquid crystal (LC) display materials^1,2 is the presence of defects attributed to smectic layer contraction on cooling from the smectic A phase to the smectic C phase during alignment. Though some materials exist which do not exhibit such defects (DeVries materials), an understanding of which structural features favor such properties is not yet available. Our group has discovered several LC mesogens containing sulfur-based moieties that do not possess these problematic defects. In this study, our goal is to synthesize several structural variants of a LC family containing a thieno[3,2-b]thiophene ring (1) within the LC core to determine how structural changes impact mesogenic behavior. Preliminary studies by another group member targeted some thieno[3,2-b]thiophene-based LCs, though in only low yields.² In this project, we hope to synthesize several of these LC targets in sufficient yields for evaluation of their mesogenic behavior.

The synthesis of these compounds uses a new approach for 2-alkoxythiophene synthesis recently developed in our laboratories (Scheme 1).² Thienone 6 was prepared in four steps from commercial materials. Mitsunobu etherification using 1-octanol yields compound 7. Compound 7 is deprotonated with LDA and treated with N-formylpiperidine followed by hydrolysis to give the aldehyde 8, which reacts with ethyl mercaptoacetate (9) in the presence of base to produce the thieno[3,2-b]thiophene ester 10. The final targeted mesogens 13 (Scheme 2) will be prepared via saponification of 10 to the carboxylic acid 11 followed by esterification with a variety of chiral and achiral 4-alkoxyphenols 12.

References:

(1) Beekman, J.; Neyts, K.; Vanbrabant, P. J. M. Opt. Eng. 2011, 50, 081202-081217

(2) (a) Tietz, J. I., M.S. Thesis, Kent State University, Kent, OH, 2012. (b) Tietz, J.I.; Seed, A.J.;

Sampson, P. Org. Lett. 2012, 14, 5058-5061.