The effect of fluorine substitutions on the refractive index properties for π-conjugated calamitic nematic materials

ABSTRACT

In order to reveal the effect of fluorine substitutions on the refractive index properties for calamitic nematic materials, we carried out a comparative study with respect to non-fluorinated and two types of laterally fluorinated 1,4-bis[4-(hexyloxy)phenyl]ethynylbenzene molecules. Phase transition behaviours were investigated by differential scanning calorimetry and polarised optical microscopy. Additionally, extraordinary and ordinary refractive index and birefringence were evaluated from each single component system. All the analogues exhibited high birefringence values beyond 0.3 at 550 nm, of which an analogue with a fluorine substitution at the central benzene ring showed the highest Δn-value of 0.43. With respect to an analogue with the highest level of fluorination, Δn as well as n_e and n_o values were declined due to decreased order parameter and diluted molecular density. Not only the mesomorphic behaviours but also optical properties strongly relied on the manner of fluorine substitution including the number and position.

KEYWORDS:

• Nematic phase
• refractive index
• birefringence
• fluorine substitution
• bistolane
• order parameter

Acknowledgement

The authors thank Prof. Masatoshi Tokita for refractive index measurements.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was partly supported by JSPS KAKENHI [grant number 15H06285].