Improved Electronic Transport in Ion Complexes of Crown Ether Based Columnar Liquid Crystals

Abstract

The Li+- and K+-complexes of new discotic mesogens, where two n-alkoxy-substituted triphenylene cores are connected by a central crown ether (12-crown-4 and 18-crown-6), provide interesting structural and electronic properties. The inter- and intra-columnar structure was investigated by small and wide angle X-ray scattering. The electronic and ionic transports were studied by temperature dependent photoconductivity and impedance spectroscopy, respectively. Besides a strong increase of the stability and the width of the columnar phases the presence of soft anions (iodide, thiocyanate, tetrafluoroborate) leads to an improved intra-columnar order. The hereby shortened stacking-distance of the triphenylene cores leads to a significant increase of the photoconductivity in the columnar mesophase. Furthermore, the ionic conductivity of the new materials was investigated on macroscopically aligned thin films. The existence of channels for fast cation transport formed by the stacked crown ether moieties in the centre of each column can be excluded. The cations are coordinated strongly and therefore contributing only little to the conductivity. The ionic conductivity is dominated by the anisotropic migration of the non-coordinated anions through the liquid, like side chains favouring the propagation parallel to the columns. Iodide migrates about 20 times faster than thiocyanate and 100 times faster than tetrafluoroborate.

Adjacent functional group effects on the assembly of columnar liquid crystals

“…These phases have been targeted for applications such as solar cells, [10][11][12][13][14][15] ferroelectrics, [16][17][18] and ionic conductive materials. [19][20][21] Our primary targets are dibenzophenazines, D(X,Y), which constitute a versatile family of discotic mesogens that tend to form columnar phases with wide temperature ranges. [22][23][24][25][26] Functional groups dramatically influence the self-assembly of these systems.…”

Polyfunctional Nanosystems on Amphiphilic and Hybrid Platform: Self-Assembly, Mesogenic Properties and Application

“…Чем меньше различие между геометрическими размерами катионов и полости макроциклов, тем выше устойчивость образующихся при связывании ионов металлокомплексов. Примером макроциклических лигандов, комплексующих ионы металлов для создания ЖК, могут служить порфириновые производные [137][138][139] и краун-эфиры [140][141][142]. Причем в качестве мезогенов могут быть задействованы как алкилированные производные макроциклов, так и суперамфифильные комплексы макроцикл-ПАВ.…”

Ion polarisation-assisted hydrogen-bonded ferroelectrics in liquid crystalline domains

“…45 Among the various types of molecular assembly, the lattice periodicity of liquid crystal phases such as nematic (N) and smectic (Sm) states is much lower than that of the single crystalline state, and the exible molecular assembly structure enables the design of the dynamic motion of ions. Many ionic liquid crystalline materials have a relatively high ionic conductivity of up to 1.5 Â 10 À4 S cm À1 in the Sm phase at around 350 K. [46][47][48] Interestingly, ionconductive liquid crystalline materials based on the diaza [18] crown-6 derivative bearing decylalkoxy-p-cyanobiphenyl chains have been reported by Espinet et al, 49 and the introduction of K + I À into the crown ether imparted an ionic conductivity of 3.0 Â 10 À7 S cm À1 at 530 K, which is lower than that of a K + -free crown ether. The lower conductivity of the K + -doped crown ether is due to the effective K + -capturing ability of the diaza [18] crown-6 unit and the insufficient formation of a channel-type molecular assembly in the absence of a regular array of crown ethers.…”