Nature of the Intense Second‐Order Nonlinear Optical Activity: DFT Studies on the Octupolarization of Sandwich‐Type Bis(phthalocyaninato) Yttrium Skeletons

The periodic octupolar vibrational nature of the electron cloud in sandwich-type bis(phthalocyaninato) yttrium double-decker compounds has been revealed on the basis of coupled perturbed density functional theory. This in turn results in an intense hyper-Rayleigh scattering response and renders the double-decker skeletons excellent second-order hyperpolarizability with a maximum value as high as 5.55×10(6) au (≈10(5) ×10(-30) esu, theoretical prediction) achieved for the molecular conformation with a rotation angle between two phthalocyanine chromophores of approximately 70°.