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-isotropic phase transition temperature (T _NI) decreases with increase in non-nematic concentration. But when there are hydrogen bonded complexes or π-complexes of suitable strength formed between the nematic and the solute molecules, 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 binary 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 found that for binary systems in which 5CB and a solute molecule form distinct one-to-one complexes, T _NI falls rather rapidly. When the solute molecules have a strong acceptor power, the rate of T _NI fall with solute concentration is found to be correlated well with the electonegativity of the solute molecules.