Second hyperpolarizabilities of polycyclic diphenalenyl radicals: Effects of para/ortho-quinoid structures and central ring modification

Structural effects on the second hyperpolarizability (γ) of singlet polycyclic phenalenyl radicals are investigated by the hybrid density functional theory method. A control scheme of γ for singlet polycyclic diphenalenyl radical compounds is proposed by adjusting the contribution of para/ortho-quinoid resonance forms and by modifying the central ring structures.