Mesomorphism in columnar phases studied by solid-state nuclear magnetic resonance

• In this paper, we present C-13 and H-1 NMR investigations of 2, 3, 6, 7, 10, 11-hexahexyl-thiotriphenylene (HHTT). The measurements were carried out under both static and magic-angle spinning conditions. The phase diagram of HHTT is K <-> H <-> D-hd <-> I, where H is a helical phase and D-hd is a columnar liquid crystal. The motivation was to characterize the molecular order and dynamics and to investigate differences at the molecular level between the two mesophases: H and D-hd. It is shown that D-hd is a conventional columnar liquid crystal, where the molecular core undergoes fast rotation about the symmetry axis. The orientational order in this mesophase is lower and the temperature dependence of the order parameter is steeper than in other triphenylene-based compounds. On the other hand, in the helical phase the core, similarly to the solid phase, is essentially rigid. The difference between the solid and helical phases is mainly manifested in an increased mobility of the aliphatic chains observed in the latter phase. In addition, the sample exhibits thermal history effects, which are observed in the different behavior upon cooling and heating.

Subject headings

NATURVETENSKAP  -- Kemi -- Fysikalisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Physical Chemistry (hsv//eng)

Keyword

discotic liquid-crystal

heteronuclear dipolar couplings

field nmr-spectroscopy

c-13 nmr

hexaoctyloxy-rufigallol

rotating solids

deuterium nmr

side-chains

mesophase

triphenylene

Physical chemistry

fysikalisk kemi

Publication and Content Type

ref (subject category)

art (subject category)