Orientational Order Parameters of Some 4-Cyano 4′, n-Alkoxybiphenyls

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Abstract
During the last decade much effort has been made to the synthesis of new mesomorphic materials with suitably low melting points for display application. The extensive work by Gray and coworkers /1/ has established that the cyanobiphenyl system with alkyl and alkoxy substituents create stable, colourless, low melting liquid crystals. Naturally, it would be of some importance for the practice to know the orientational properties of these species charties characterized by the orientational order parameters ⟨P2 = 1/2 ⟨cos2θ - 1⟩ and ⟨P4 = 1/3 ⟨35 cos2θ - 30 cos2θ → 3⟩ where θ is the angle between the long exis of any given molecules with the direction of the molecular given molecules witn tne direction of the molecular alignment. The angular brackets denote averaging over all molecules in tne medium. First Heger /2/ and later Miyano /3/ using Haman spectroscopical method have reported tne ⟨P2⟩ and ⟨P4⟩ temperature dependence for tne nematic liquid cryetals 4-cyan0 4′n-pentylbipnenyl and 4-cyan0 4′n-neptylbiphenyl correspondingly. Comparative studies of the orientational order parameters ⟨P2⟩ determined by IR and FIR spectroscopy of some 4-cyano alkylbipnenyls have been also reported recently /4/. Elastic and optical properties of 4-CYanO 4′n-pentyl to 4′n-octylbiphenyls as well as ⟨P2⟩ temper-ature dependence nave been published i n refs. 5a,b. In spite of the much research work already done on 4-cyan0 4′n-alkylbipnenyls ⟨P2⟩ of only one alkoxycya-nobipnenyl derivative namely 4-cyan0 4′n-octyloxybi-phenyl has been measured by IR absorption spectroscopy /6/ and by EPR technique /7/.