Chiral discotic derivatives of 1,3,5-triphenyl-6-oxoverdazyl radical
Two derivatives of 1,3,5-aryl-6-oxoverdazyl containing two 3,4,5-trioctyloxyphenyl and one 3,4,5-tri((S)-3,7-dimethyloctyloxy)phenyl group in position C(3) (1b) or N(1) (1c) were investigated by thermal, X-ray diffraction and magnetic methods. The results were compared to those obtained for achiral derivative 1a containing three 3,4,5-trioctyloxyphenyl groups. All three compounds exhibit an ordered columnar hexagonal phase, Colh(o), and for chiral derivatives, 1b and 1c, a superstructure with doubled periodicity was found. The introduction of the three chiral alkoxy substituents in 1a lowered the mesophase stability by about 50 K and induced a Colh phase in 1c. Thermochromic analysis showed a hypsochromic shift upon formation of the Colh(o) phase similar for all three derivatives 1 (~0.3 eV), which coincides with a 5% drop in effective magnetic moment, μeff, for 1c. Analysis of magnetisation data in a range of 2–370 K at 200 Oe revealed weak antiferromagnetic interactions (θ = – 4 K) in the Colh(o) phase.