Nematic 2,5-disubstituted thiophenes

A large number of new liquid crystals incorporating the 2,5-disubstituted thiophene ring have been prepared and their mesomorphic behaviour studied in order to systematically investigate the correlation between the molecular structure and mesomorphism of thiophene derivatives with different shapes, polarisability and polarity. As a consequence of these investigations we have prepared a new class of liquid crystals incorporating a 2,5-disubstituted thiophene ring and a conjugated trans-carbon-carbon double bond in the terminal chain. These novel thiophene derivatives are the first liquid crystals incorporating a 2,5-disubstituted thiophene ring to exhibit a nematic phase at room temperature. This enables the flexoelectric coefficients of a bent-shaped molecule to be measured directly and at room temperature for the first time to the authors' knowledge. Many of these new thiophenes exhibit a high birefringence and a high nematic clearing point and are of potential use as components of nematic mixtures in LCDs.