Relaxation frequencies for flip-flop rotation of three- and four-ring compounds and dual frequency addressing mixtures with high birefringence

Abstract

Relaxation frequencies f_r characterising the molecular rotation around the short axes (flip-flop movement) of 45 three- and four-ring polar compounds with high birefringence (mainly cyclohexyl, phenyl and biphenyl tolanes and quaterphenyls terminated with F, OCF₃, NCS group) have been measured. These compounds exhibit a large positive dielectric anisotropy Δε = ε_║ − ε_⊥ in the nematic phase and relatively low f_r values (in the range of dozens kHz). The dependence of f_r upon molecular structures and physical properties of systems (molecular rigid core length, polarity and viscosity) is discussed. Mixtures for dual frequencies addressing display with the crossover frequency f_co of the order of ~1 kHz have been prepared by joining the above compounds with a mixture consisted of two, three and four fluoro-substituted in the lateral position tolanes and phenyltolanes showing negative dielectric anisotropy. It was stated that relaxation frequency is correlated mainly with their length and polarity.

Keywords:

• molecular dynamic
• flip-flop movement
• relaxation frequency
• dielectric anisotropy
• optical anisotropy
• DF mixture
• NCS group geometry

Additional information

Funding

The work was supported by Polish Ministry of Sciences and Higher Education, Key Project POIG.01.03.01-14-016/08 ‘New Photonic Materials and their Advanced Applications’ and PBS 847.