Electronic conduction in nematic phase of small molecules

Abstract

We investigated charge-carrier transport in the nematic phase of small molecules such as 2-phenylbenzothiazoles by time-of-flight experiments, in which the conduction mechanism has been considered to be ionic. As a result, we established the hole and electron transports in the nematic phase of highly purified samples: we found that there were two transits, namely, fast and slow transits, in less pure samples; the slow transit was attributed to ionic conduction originating from trace amounts of impurities and the fast transit was attributed to electronic conduction whose attribution was elucidated by mobility changes in the diluted samples with a hydrocarbon of n-tetradecane ͑n-C 14 H 30 ͒. From these results, we conclude that the intrinsic conduction mechanism in the nematic phase of small molecules is ambipolar and electronic, irrespective of the size of the -conjugate system of the core moiety. Thus, they provide a new insight into the conduction mechanism in fluidic materials.

Impact of the arrangement of functional moieties within small molecular systems for solution processable bulk heterojunction solar cells

“…The hole mobility value measured for the nematic ADA molecule is 1.4 Â 10 À5 cm 2 V À1 s À1 , which is a low value but is typical of nematic compounds of low molecular weight. 25 The hole mobility measured for the crystalline DAD molecule gives only a slightly higher value of 4 Â 10 À5 cm 2 V À1 s À1 . This last value is surprisingly low, when considering the crystalline nature of the corresponding compound.…”

Organic liquid crystals in optoelectronic device applications: Field‐effect transistors, nonvolatile memory, and photovoltaics

“…It is worth noting that the ionic conduction is also extrinsic in the nematic phase, and the origin of ionic conduction is also related to the low contents of chemical impurities as in the case of smectic liquid crystals. [21][22][23] With regard to the smectic mesophases, there are two conduction channels within them: i) the solid-like conduction channel for charges, in which the aromatic π-conjugated systems of the liquid crystalline molecule are aggregated and ii) the liquid-like conduction channel for ions, in which the flexible alkyl side chains of the liquid crystalline molecules are aggregated. In addition to the contamination of chemical impurities, the ionic conduction is often observed in liquid crystals.…”

Chiral Liquid Crystalline Electronic Systems

“…In the LC phases with a nematic order, ionic conduction had been predominant. However, electronic charge carrier transport has been confirmed in the nematic phases consisting of the rod-like and disk-like molecules comprising extended π-conjugated cores [31][32][33][34]. In chiral LC phases, electronic charge carrier transport should be possible if π-conjugated moieties aggregate closely, resulting in a large overlap between the π-conjugated units.…”