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Twist‐Bend Nematic Glasses: The Synthesis and Characterisation of Pyrene‐based Nonsymmetric Dimers
Author(s) -
Walker Rebecca,
Majewska Magdalena,
Pociecha Damian,
Makal Anna,
Storey John MD,
Gorecka Ewa,
Imrie Corrie T.
Publication year - 2021
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.202000993
Subject(s) - liquid crystal , mesogen , crystallography , dimer , ether , pyrene , phase (matter) , methylene , materials science , twist , intermolecular force , chemistry , organic chemistry , molecule , liquid crystalline , geometry , optoelectronics , mathematics
A selection of pyrene‐based liquid crystal dimers have been prepared, containing either methylene‐ether or diether linked spacers of varying length and parity. All the diether linked materials, CBO n O.Py ( n =5, 6, 11, 12), exhibit conventional nematic and smectic A phases, with the exception of CBO11O.Py which is exclusively nematic. The methylene‐ether linked dimer, CB n O.Py, with an even‐membered spacer ( n =5) was solely nematogenic, but odd‐members ( n =6, 8, 10) exhibited both nematic and twist‐bend nematic phases. Replacement of the cyanobiphenyl fragment by cyanoterphenyl giving CT6O.Py, gave elevated melting and nematic‐isotropic transition temperatures, and SmA and SmC A phases were observed on cooling the nematic phase. Intermolecular face‐to‐face associations of the pyrene moieties drive glass formation, and all these materials have a glass transition temperature at or above room temperature. The stability of the glassy twist‐bend nematic phase allowed for its study using AFM, and the helical pitch length, P TB , was measured as 6.3 and 6.7 nm for CB6O.Py and CB8O.Py, respectively. These values are comparable to the shortest pitch of a twist‐bend nematic phase measured to date.