Spin state dependence of second hyperpolarizabilities of zethrenes

The hybrid density functional theory calculations are applied to the elucidation of the relationship between the spin state and the second hyperpolarizabilities (γ) of diradical molecules, singlet and triplet zethrenes. The longitudinal γ values of singlet zethrenes with intermediate diradical character are found to be significantly reduced in the triplet state due to the Pauli principle, while the feature is reduced when increasing the length of middle ring regions, i.e., when increasing the diradical character.