Lateral substituent effects on UV stability of high-birefringence liquid crystals with the diaryl-diacetylene core: DFT/TD-DFT study

ABSTRACT

To study the effect of the lateral substituents on the UV stability of high birefringence liquid crystals (LCs), computational chemistry was used to examine a series of high birefringence LCs based on a diphenyl-diacetylene (DPDA) central core, thiophene segments as elongated π-conjugated units and four electron-withdrawing groups (-F, -CF₃, -OCF₃, -CN) as lateral substituents. In the present study, geometry optimisations have been performed using the DFT/B3LYP/6-311G (d, p) method. Out of a series of functional and basis sets examined, the functional ωB97X-D and basis set 6-31G (d, p) are most successful in predicting charge transfer absorption. The theoretical study indicates that the enhancement of UV stability is related with the types, numbers and positions of the lateral substituents. The calculated results indicate that the electron-withdrawing groups can shorten triple bond length, decrease energy gap value and increase the absorption maxima of the high-Δn LCs, which is beneficial for good UV stability. With the introduction of increasing lateral electron-withdrawing substituent numbers, the DPDA derivatives would further improve UV stability. This work may provide an effective solution for the obstacle existed in the high-Δn LCs with DPDA structures and pave a way for their applications in LC photonics.

Graphical Abstract

KEYWORDS:

• High-birefringence liquid crystals
• UV stability
• diaryl-diacetylene
• lateral substituent
• DFT calculations

Acknowledgements

The authors would like to thank the Defense Industrial Technology Development Program of China (B0520132007, B1120132028), Shaanxi National Science Foundation (2014JM7270), Key Technologies R&D Program of Xi’an (CXY1430(2)), the Key Technologies R&D Program of Shaanxi Province (2014K10-06), Program for Changjiang Scholars and Innovative Research Team in University (IRT-14R33) and the Fundamental Research Funds for the Central Universities (GK201504008) for financial support of this work.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental metrial

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the Shaanxi National Science Foundation [2014JM7270];the Key Technologies R&D Program of Shaanxi Province [2014K10-06];the Fundamental Research Funds for the Central Universities [GK201704008];the Defense Industrial Technology Development Program of China [B0520132007, B1120132028];Program for Changjiang Scholars and Innovative Research Team in University [IRT-14R33];Key Technologies R&D Program of Xi’an [CXY1430(2)].