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, Col h ), columnar hexagonal ordered (1[10]b, Col h(o) ), columnar hexagonal 3D (1[10]a, 1[10]e and 1[10]f, Col h(3D) ) or a sequence of two phases (1[10]b, Col h -Col h(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 alldecyloxy derivative 1[10]b exhibits a hypsochromic shift upon Col h(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.

Chiral discotic derivatives of 1,3,5-triphenyl-6-oxoverdazyl radical

“…This small bathochromic shift between the Iso and Col h phases is typical for other discotic verdazyls. [14] Upon cooling of the sample from Iso to Col h(o) phase, λ max changes in the opposite direction with about 5 K hysteresis ( Figure 4). …”

“…[11] Recently, we demonstrated that substituted triphenyl derivatives of verdazyl, a π-delocalised radical, form discotic hexagonal phases. [12][13][14] We have investigated three series of compounds containing 3,4,5-trialkoxyphenyl [12] (such as 1a), 3,4,5-trialkylsulfanylphenyl [13] and a mixture of both substituents. [14] The results demonstrated that the alkylsulfanyl derivatives form a disordered columnar hexagonal 3D phase (Col h(3D) ) below 60°C, presumably with a helical structure.…”

“…[12][13][14] We have investigated three series of compounds containing 3,4,5-trialkoxyphenyl [12] (such as 1a), 3,4,5-trialkylsulfanylphenyl [13] and a mixture of both substituents. [14] The results demonstrated that the alkylsulfanyl derivatives form a disordered columnar hexagonal 3D phase (Col h(3D) ) below 60°C, presumably with a helical structure. In contrast, the alkoxy derivatives, including the octyloxy derivative 1a, form a broad-range ordered columnar hexagonal phase (Col h(o) ), with a correlation length along the columns of at least 370 Å at 30°C and pronounced thermochromism upon the formation of the mesophase.…”

Bent-core 6-thioxoverdazyl: a comparison of mesogenic properties with the 6-oxo analogue

“…In a series of recent papers, 1,3,5-trisubstituted 6-oxoverdazyl radical has been demonstrated as an effective structural element for both disc-like [1][2][3][4] and bent-core [5] liquid crystalline materials. Whereas the former class of compounds exhibit columnar phases exclusively (e.g.…”

Induction of smectic polymorphism in bent-core derivatives of the 6-oxoverdazyl by partial fluorination of alkyl chains

“…Materials based on p-delocalized radicals are of particular interest in the context of molecular electronics and spintronics 2 due to their photophysical and electrochemical properties. 3 In this context we have been working with 6-oxoverdazyl and demonstrated that it is a suitable paramagnetic structural element for disc-like [4][5][6][7][8][9] and bent-core, such as 1[n] (Fig. 1), 10,11 liquid crystalline materials.…”