H-shaped conjugated mesogens: synthesis and mesomorphic properties of 3,3′,5,5′-tetrakis(phenylethynyl)-2,2′-bithiophene derivatives

Abstract

A new class of H-shaped conjugated mesogens, namely alkyl- and alkoxy-substituted derivatives of 3,3′,5,5′-tetrakis(phenylethynyl)-2,2′-bithiophene (4PE2T), have been synthesised, and the relationships between molecular structures and mesomorphic properties investigated. The mesomorphic properties of the 4PE2T derivatives have been examined by differential scanning calorimetry and polarising optical microscopy. In the 4PE2Ts, R¹C₆H₄CC[C₈H₂S₂(CCC₆H₄R²)₂]CCC₆H₄R¹, where R¹ and R² = alkyl and alkoxy chains of various lengths, the tetraalkyl derivatives exhibit enantiotropic or monotropic nematic phases, whereas the tetraalkoxy derivatives all exhibit enantiotropic nematic phases. The derivatives with two alkyl and two alkoxy chains also show enantiotropic nematic behaviour. It is found that the formation of the mesophase and the crystal–nematic and nematic–isotropic transition temperatures are strongly affected by the length, number and position of the alkyl and alkoxy chains.

Keywords:

• H-shaped conjugated mesogens
• 2,2′-bithiophenes
• phenylethynyl groups
• molecular structures
• mesomorphic properties
• structure–property relationships

Acknowledgement

We are grateful to Dr R. Nagahata and Ms Y. Saito of AIST for carrying out the MALDI–TOF–MS measurements.

Funding

We also wish to thank the AIST IBEC Centre for the provision of analytical services and AIST for financial support.

Supplemental data

Supplemental data for this article can be accessed here.