The design of liquid crystalline bistolane-based materials with extremely high birefringence

We designed three new bistolanes with alkylsulfanyl groups. A symmetric derivative contains short terminal methylsulfanyl groups (-SCH3) on both ends, while two asymmetric derivatives contain a methylsulfanyl group on one end, as well as a highly polarizable cyano (-CN) or isothiocyanate (-NCS) group on the other end. These materials exhibited a well-defined enantiotropic nematic phase, as well as an extremely high birefringence (Delta n > 0.6). Most notably, the NCS derivative achieves an extremely high value of 0.77 at 550 nm. These results should be helpful for the design and synthesis of novel nematic materials with high birefringence.