Molecular ordering dependent charge transport in π-stacked triphenylene based discotic liquid crystals and its correlation with dielectric properties

We investigate the charge transport in triphenylene core based homologous series of discotic mesogens (HAT(n)) by the time-of-flight method. HAT5, HAT6 and HAT8 exhibit Col(hp) phase whereas HAT4 shows Colhp phase. For the investigated homologous series, we have observed a single transit in the transient photocurrent curves corresponding to positive charge carriers having the mobility in order of 10(-2) to 10(-4) cm(2)/vs. The hole mobility decreases with increasing the number of carbon atoms (n) in the alkyl chain attached to the triphenylene core, which follows the empirical exponential relationship: mu approximate to a:exp(-b/n). Furthermore, the dielectric measurement has been done on these compounds to bring a correlation between the molecular ordering by varying the alkyl chain of the HAT(n) compounds. In the light of structure-property correlation, we have noticed that the hole mobility and permittivity vary according to the length of alkyl chain attached to the triphenylene core. The molecular ordering is also discussed via phase behaviour of compounds and confirmed by polarized optical textures. The change in entropy also decreases with increasing alkyl chain length of the HAT(n) compounds rendering an agreement with that of the mobility and dielectric measurements. The HAT(n) compounds show their potential applications in opto-electronics and could serve as organic semiconductors; however, the poor conductivity remains as a futuristic challenge. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The charge transport in discotic mesogens based on triphenylene core was investigated using the time-of-flight method. The hole mobility was found to decrease with increasing the number of carbon atoms in the alkyl chain attached to the triphenylene core, following an exponential relationship. Dielectric measurements revealed a correlation between molecular ordering and alkyl chain length, impacting hole mobility and permittivity. The potential applications of these compounds in opto-electronics as organic semiconductors are noted, despite the challenge of poor conductivity.