Discotic derivatives of 6-oxoverdazyl radical

Substitution of each phenyl in 1,3,5-triphenyl-6-oxoverdazyl with three alkoxy groups induces an ordered columnar hexagonal phase (Col_h(o)) below 130°C in 1bn], while in the alkylsulfanyl analogues 1an] additional periodicity along the columns was found rendering the phase a true three-dimensional columnar hexagonal phase (Col_h(3D)) below 60°C. Both series exhibit broad absorption bands in the visible region with maxima at 540 and 610 nm in series 1an] and at 486 and 614 nm in series 1bn]. Unusual reversible thermochromism is observed in series 1bn], in which the dark green isotropic phase turns red in the discotic phase. Analysis of 1a8] revealed redox potentials E^0/+1_1/2 = +0.99 V and E^{0/ ?1}_1/2 = –0.45 V vs. saturated calomel electrode (SCE), while the potentials in the alkoxy analogue 1b8] are shifted cathodically by 0.16 V. Photovoltaic studies of 1a8] demonstrated hole mobility of μ_h = 1.52 × 10^?3 cm² V^?1 s^?1 in the mesophase with an activation energy E_a = 0.06 ± 0.01 eV. Magnetisation studies of 1a8] revealed nearly ideal paramagnetic behaviour in either the solid or fluid phase above 200 K and weak antiferromagnetic interactions at low temperatures. In contrast, a noticeable drop of about 4% in μ_eff was observed during the I→Col phase transition in 1b8], which coincide with the thermochromic effect.