Chiral induction in nematic and smectic C liquid crystal phases by dopants with axially chiral 1,11-dimethyl-5,7-dihydrodibenz[c,e]thiepin cores

Abstract

Three calamitic molecules with axially chiral cores, (S)-3,9-bis[(4-dodecyloxybenzoyl)oxy]-1,11-dimethyl-5,7-dihydrodibenzo[c,e]thiepin (5a), (R)-3,9-bis[(4-butoxybenzoyl)oxy]-1,11-dimethyl-5,7-dihydrodibenzo[c,e]thiepin (5b), and (R)-3,9-bis[(4-octyloxybenzoyl)oxy]-1,11-dimethyl-5,7-dihydrodibenzo[c,e]thiepin (5c), were synthesized in optically pure form and doped in four calamitic liquid crystal hosts with I–N–SmA–SmC (INAC) phase sequences (PhP, PhB, NCB76 and DFT), and in the nematic host 5CB. Helical twisting powers (β) in the N* phase are in the range of 24–43 µm^–1 with the INAC hosts, and in the range of 56–58 µm^–1 with 5CB at T–T_N-I = –2 K, which are comparable to those previously reported for axially chiral binaphthyls. Interestingly, these dopants were found to stabilize and broaden the temperature range of the N* phase in 5CB. With some of the dopant–INAC host mixtures, the induction of a chiral TGB_A* phase was also observed. Dopant 5a induces a measurable spontaneous polarization in the SmC phase of the achiral phenylpyrimidine host PhP, giving a polarization power δ_p of –104 ± 20 nC cm^–2. Comparisons of helical twisting powers in the N* and SmC* phases, and polarization powers in the SmC* phase, for dopants 5a–c and the dinitro analogue (+)-1,11-dinitro-3,9-bis[(4-nonyloxybenzoyl)oxy]-5,7-dihydrodibenzo[c,e]thiepin (4) suggest that the nitro substituents play a dominant role in promoting chirality transfer in the SmC* phase, whereas the helical topography of the core appears to be a more important factor in promoting chirality transfer in the N* phase.