Hyperpolarisability - molecular twist correlation in diaminodicyanoquinodimethanes

Semiempirical quantum chemical calculations are carried out on the class of diaminodicyanoquinodimethanes. The calculated first hyperpolarisabilities of these molecules manifest a close correlation with the twist angle betwee n the diaminomethylene unit and the aromatic ring. The correlation follows earlier model calculations on a prototypical molecule and can be qualitativ ely explained on the basis of the well-known two-level approximation.