Tuning the Magnetic Properties of Columnar Benzo[e][1,2,4]triazin‐4‐yls with the Molecular Shape

A homologous series of disc‐like 1,3,6‐trisubstituted benzo[e][1,2,4]triazin‐4‐yls 1[n] was synthesized and their structural, thermal, optical, magnetic, and electric properties were investigated. The results demonstrate that all members of the series display a Colh phase with clearing temperatures depending on the length of the alkoxy chains at the N(1) position, hence the shape of the disc. Powder XRD and magnetic data indicate a gradual change in the column diameter and magnetic behavior in the series in transition from half‐disc in 1[0] (antiferromagnetic interactions) to full‐disc geometry in the 1[12] homologue (ferromagnetic interactions with J/kB=+7.5 K). Studies of binary systems revealed that a 1 : 1 mixture of 1[0] and 1[12] exhibits modest stabilization of the Colh phase with an expanded range, and magnetic behavior typical for 1[0] in the rigid phase obtained from the melt. Electric measurements demonstrated hole mobility of ∼10−3 cm2 V−1 s−1 and dark conductivity of ∼10−11 Scm−1 in the mixture and individual compounds. The latter is enhanced up to 4 times by simultaneous illumination with UV light. The magnitude of the ferromagnetic exchange interaction J in series 1[n] is tuned by the size of the Ar substituent at the N(1) position (shape of the molecular disc) and by the formation of binary mixtures.