Liquid crystalline radicals: discotic behavior of unsymmetrical derivatives of 1,3,5-triphenyl-6-oxoverdazyl

Abstract

A series of six 6-oxoverdazyl (1[10]) substituted with a total of three 3,4,5-tri(decyloxy)phenyl and/or 3,4,5-tri(decylsulfanyl)phenyl groups was investigated by thermal, XRD, spectroscopic, magnetic and photovoltaic methods. The compounds exhibit columnar hexagonal (1[10]c, Colh), columnar hexagonal ordered (1[10]b, Colh(o)), columnar hexagonal 3D (1[10]a, 1[10]e and 1[10]f, Colh(3D)) or a sequence of two phases (1[10]b, Colh–Colh(3D)). The mesophase structure and stability and also thermochromism were investigated as a function of the number and distribution of decyloxy and decylsulfanyl substituents in the molecule. Thermal analysis demonstrated that the presence of the 3,4,5-tri(decyloxy)phenyl substituent in the C(3) position increases the phase stability. Spectroscopic analysis showed that only all-decyloxy derivative 1[10]b exhibits a hypsochromic shift upon Colh(o) formation, while all other compounds in the series show a modest bathochromic shift in the columnar phase relative to the isotropic phase. Magnetization investigation of 1[10]d demonstrated the paramagnetic behavior of isolated spins in isotropic and columnar phases. Negligible photocurrent was detected for 1[10]d in the columnar phase.