Effects of the lateral substituent on the cubic phase formation of two analogous compounds, 4ʹ-n-hexadecyloxy-3ʹ-cyanobiphenyl-4-carboxylic acid (ACBC-16) and its 3ʹ-nitro compound (ANBC-16)

Abstract

Two cubic (Cub) phase forming compounds, 4ʹ-n-hexadecyloxy-3ʹ-cyanobiphenyl-4-carboxylic acid (ACBC-16) and its 3′-nitro analogue (ANBC-16) were studied by infrared (IR) spectroscopy. In the temperature region of the Cub phase, the molar fraction of hydrogen-bonded COOH groups estimated for ACBC-16 was by ≈0.05 at maximum larger than that for ANBC-16 and the aromatic ring C═C stretching (ν(C═C)_ring) band frequency of ACBC-16 was by 3 cm⁻¹ lower than that of ANBC-16. The quantum chemical calculation at DFT/B3LYP level, on the one hand, showed no meaningful difference in the stabilisation energy for dimerisation and the ν(C═C)_ring band frequency between the respective model compounds. These results can be ascribed to the different steric effects of the side groups; the CN group would make possible the close contact of neighbouring phenyl rings while the bulky NO₂ group would not, giving slightly more stabilised dimerisation of ACBC-16 in the Cub phase than in ANBC-16.

Keywords:

• cubic mesophase
• infrared spectroscopy
• quantum chemical calculation
• steric effect
• hydrogen bonding

Acknowledgements

We first thank Prof. W. Haase at Technische Universität Darmstadt (Germany), Drs. Y. G. Galyametdinov and I. Galyametdinova at Kazan Physical-Technical Institute (Russia), Dr. R. Eidenschink at NEMATEL (Germany) for kindly permitting the use of the ACBC-16 sample. Prof. Emeritus Michio Sorai at Osaka Univeristy (Japan) gave us a chance to study the ACBC-16; in fact the present work started from the collaboration work with those five scientists.[12,50]

Additional information

Funding

This work was partly supported by Grant-in-Aid for Scientific Research (C) [grant numbers 18550121 and 25410091] from Japan Society for the Promotion of Science (JSPS) and by Grant-in-Aid for Scientific Research on Priority Areas [grant number 446/19022012] from Ministry of Education, Culture, Sports, Science and Technology (MEXT) (both for S.K.) and by Grant-in-Aid for Scientific Research (B) [grant number 26288031] from JSPS (K.S.). [12,50]