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 (1^2–) 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 (β_tot). Among these structures, the 1^2– has the largest β_tot value of 4.2 × 10⁴, which is greatly larger than 2.0 × 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. [ABSTRACT FROM AUTHOR]