A novel nematic tri-carbazole as a hole-transport material for solution-processed OLEDs

ABSTRACT

Two structural isomers of alkyl-substituted tri-carbazoles were synthesised to study the effect of the substitution pattern on their liquid crystalline behaviour and conductivity and performance in test OLEDs. The isomer with a 2,7-disubstitution pattern in the central carbazole exhibits a monotropic nematic phase, a high conductivity up to 10 Cd A⁻¹ and is suitable as a hole-transport material for solution-processed OLEDs, achieving a high efficiency. The tri-carbazole isomer with a 3,6-substitution pattern, in the central carbazole, does not exhibit observable liquid crystalline behaviour, exhibits conductivity values two orders of magnitude lower than that of its 2,7-disubstituted isomer and performs poorly in OLEDs with the same configuration.

GRAPHICAL ABSTRACT

Two structural isomers of alkyl-substituted tri-carbazoles A and B exhibit significantly different liquid crystalline behaviour, conductivity and performance in test OLEDs dependent upon their molecular shape.

KEYWORDS:

• Tri-carbazole liquid crystalline isomers
• nematic mesophases
• hole transport materials
• solution-processed OLED

Acknowledgments

Huaiyin Institute of Technology, the China Scholarship Council and the University of Hull are thanked for their support for Dr Guang Hu.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Huaiyin Institute of Technology [Z301B19582]; the China Scholarship Council; University of Hull.