Theoretical study on the gigantic effect of external static electric field application on the nonlinear optical properties of 1,2,3,5-dithiadiazolyl π-radical dimers

Abstract

Using the spin-unrestricted density functional theory method, we investigate the effect of external static electric field application on the first and second hyperpolarizabilities (β and γ) – nonlinear optical (NLO) properties at the molecular scale – of a 1,2,3,5-dithiadiazolyl π-radical dimer. It is found that these properties drastically vary depending on the external electric field intensity, and that such drastic variation occurs with gigantically enhanced peaks around the transition region from the diradical to charge transfer state. These results qualitatively accord with the previous theoretical prediction based on the asymmetric two-site diradical model. It also turns out that the field-induced enhancement ratio of γ amplitude reaches 9 × 10⁴ in the maximum positive peak and −3 × 10⁵ in the maximum negative peak for the dimer with an intermolecular distance d = 4.8 Å. This result demonstrates the promising potential of open-shell molecular aggregates as a novel class of highly-active external-field-driven NLO switches.