Charge transfer interaction between the nematogen 5CB and non-liquid crystal

In general, when a non-nematic solute is added to a nematic, the nematic-is otropic phase transition temperature (T-NI) decreases with increase in non- nematic concentration. But when there are hydrogen bonded complexes or pi - complexes of suitable strength formed between the nematic and the solute mo lecules, the T-NI can rise. Mixing of p-terphenyl or anthracene with 5CB (4 -cyano-4'-pentylbiphenyl) results in a T-NI rise. On the other hand, in a b inary system consisting of a substance with strong acceptor properties (e.g . tetracyanoethylene; TCNE) and nematic 5CB, T-NI fell remarkably. We have now studied the effect of intermolecular interactions on the T-NI of 5CB by using various acceptor molecules and donor molecules as solutes. We have f ound that for binary systems in which 5CB and a solute molecule form distin ct one-to-one complexes, T-NI falls rather rapidly. When the solute molecul es have a strong acceptor power, the rate of T-NI fall with solute concentr ation is found to be correlated well with the electonegativity of the solut e molecules.