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 benzoe]1,2,4]triazin-4-yls 1n] was synthesized and their structural, thermal, optical, magnetic, and electric properties were investigated. The results demonstrate that all members of the series display a Col_h 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 10] (antiferromagnetic interactions) to full-disc geometry in the 112] homologue (ferromagnetic interactions with J/k_B=+7.5 K). Studies of binary systems revealed that a 1 : 1 mixture of 10] and 112] exhibits modest stabilization of the Col_h phase with an expanded range, and magnetic behavior typical for 10] 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.