A new series with smectic blue phases and SmC^*-BP_Sm2 direct transition

Abstract

A series of trifluoro-substituted benzoate derivatives: (R)-1-methylheptyl 4-[4-(4-alkyloxy3-fluorobenzoyloxy)-3-fluorobenzoyloxy]-3-fluorobenzoates is reported. The short chain members (n = 8 to 12) display the phase sequence Cr-SmC^*-TGBC-TGBA-BP_Sm-I (except for n = 8, 9 where there is no TGBC phase), whereas for the longer ones (n = 13, 14, 16) a direct SmC^*-BP_Sm2 transition is observed for the first time. We observe for n = 8 to 10, BP_Sm1 and BP_Sm3; for n = 11, the full set of three BP_Sm phases, and for n > 11, only BP_Sm2 and BP_Sm3 phases. The mesomorphic properties were studied by optical microscopy, DSC, and electrooptical, optical rotatory power and X-ray scattering measurements. The effect of the positions of fluorine atoms and their influence over mesomorphic behaviour are discussed.