Probing the REDOX effect of helical tetraspirobenzene on nonlinear optical properties

The helical structure is a classical framework to design high-performance organic electro-optical materials. In this work, the structure-property's relationships of helical tetraspirobenzene (1) and its oxidation (12+) and reduction (12-) products are explored. The results show that the redox brings some distinctive changes in their geometric structure and electronic property, which regulate the first hyperpolarisability (beta tot). Among these structures, the 12- has the largest beta tot value of 4.2 x 104, which is greatly larger than 2.0 x 102 a.u. of. 12+. Therefore, the reduction effect is more obvious than the oxidation effect. Furthermore, the UV-Vis absorption spectrum also proves this phenomenon: the oxidation product has a new red-shifted absorption peak (571 nm) and the reduction product has two new red-shifted absorption peaks (577 and 797 nm). We hope the present work can provide theoretical guidance for the search for high-performance nonlinear optical materials by using the redox effect.