Synthesis and liquid crystal behaviour of tetrathiafulvalenes/1,3-dithiol-2-thione and p-cyanoazobenzene

ABSTRACT

The synthesis and characterisation of tetrasubstituted tetrathiafulvalenes (TTFs) 1a–1c, which bear photoresponsive 4ʹ-cyanoazobenzenyl units, are described. These units were linked to the TTF core through spacers of different lengths. All synthesised compounds displayed mesogenic phases over a wide temperature range and no crystallisation, but vitrified to form glassy mesogens during cooling from the isotropic melt. Compound 1a with a short spacer (n = 6) exhibited enantiotropic nematic and smectic A mesophases. In contrast, compound 1b showed monotropic smectic A and oblique columnar phases. However, compound 1c with the longest spacer (n = 10) only possessed an oblique columnar phase. The results for this compound series showed that the molecular packing pattern depended on the spacer length and that cool-crystallisation was observed upon further heating. Furthermore, cyclic voltammetry and impedance tests confirmed that compound 1a has potential applications in organic semiconductor materials.

A new series of compounds derived from heterocycle TTF was successfully designed and synthesised using simple synthetic methods. All compounds formed glassy mesogens with an above-ambient glass transition temperature during cooling from the isotropic melt. With increasing spacer length, the self-assembled structures changed from Lam to Col_o. These TTF‐based LCs, in combination with good electron-donating properties and the inherent optoelectronic properties of azobenzene, might be attractive new candidates for organic optoelectronic devices.

Graphical abstract

KEYWORDS:

• Tetrathiafulvalenes
• 4ʹ-cyanoazobenzenyl
• columnar
• liquid crystal
• semiconductor materials

Acknowledgments

The authors thank the financial support by National Science Foundation Committee of China (21502008) and Science and Technology Department of Jilin Province (00005005031). We thank Simon Partridge, PhD, from Liwen Bianji, Edanz Editing China (http://www.liwenbianji.cn/ac), for editing the English text of a draft of this manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

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Additional information

Funding

This work was supported by the National Science Foundation Committee of China [21502008]; Science and Technology Department of Jilin Province [00005005031].