Engineering fibre morphology in self-assembled physical gels of a prototypical discotic liquid crystal

ABSTRACT

Supramolecular self-assembly of functional soft matter is key for next-generation optoelectronic devices. Columnar discotic liquid crystals (DLCs) are an ordered class of mesogenic materials, and their supramolecular assembly into fibres can lead to physical gel formation. However, the morphology of the fibres and factors affecting gel formation in DLCs are not well understood. In this work, we focus on prototypical symmetric hexakis(alkyloxy)triphenylene (HATn) n: 4–7 DLCs. The length of the peripheral alkyl chain of the HATn DLC gelator has a significant role in gel phase thermal stability and fibre morphology, and varying alkyl chain length from C₄H₉ to C₇H₁₃ increases the clearing temperature from 35°C to 60°C. Polarised micro-Raman spectroscopy of DLC fibres reveals optical activity. A novel DLC fibre templated, nematic-LC backfilling technique is utilised to study the alignment of 4′-Pentyl-4-biphenylcarbonitrile (5CB), revealing insights about molecular orientation at the surface on HATn fibres. To study correlation between DLC physical gel fibre morphology and optoelectronic device performance, DLC physical-gel Dye Sensitised Solar Cells (DSSCs) are fabricated. Effects of varying gelator concentration and incorporating an amphiphilic Ruthenium-based dye (Z907) are studied. Concentration and interfacial compatibility of the dye/DLC interface show strong correlation with DSSC photovoltaic performance.

Graphical abstract

KEYWORDS:

• Discotic liquid crystals
• physical gels
• self-assembly
• dye sensitised solar cells
• Raman spectroscopy

Acknowledgments

Ammar A. Khan would like to thank the higher education commission (HEC) of Pakistan for research support as part of the National Research Program for Universities (NRPU) programme Project # 9641. Furthermore, Habib ur Rehman would like to acknowledge HEC NRPU grant # 3586 for financial support. We would like to thank Dr. Richard Bushby (University of Leeds) for his kind generosity in providing HAT4 and HAT7 for this study.

Disclosure statement

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

Additional information

Funding

This work was supported by the Higher Education Commission, Pakistan [(NRPU) programme Project # 9641 and HEC NRPU Project # 3586].