Third-order nonlinear optical properties of molecules containing aromatic diimides: Effects of the aromatic core size and a redox-switchable modification

The third-order nonlinear optical (NLO) properties of aromatic diimide molecules have been studied for the first time using density functional theory (DFT) with a finite field (FF). This study shows that the size of the aromatic core can affect the static second hyperpolarizability (γ). Increasing the number of benzenes along the longitudinal axis can effectively improve the γ values because the degree of charge transfer along the longitudinal direction increases, whereas an increase in the number of benzenes along the perpendicular axis does not enhance the γ values. Furthermore, the NLO responses of the reduced form radical anions 1−, 5− and 6−, which were obtained by a reversible redox process, are discussed. The results show that the γ values of the radical anions are changed by the redox process. For the reduced form radical anion 6−, the γ value is −1906.71 × 10−36 esu, and its absolute value is ∼7.3 times larger than that of its neutral parent. An analysis of the BLA values demonstrates that the γ value is closely related to the conjugation of the aromatic core used in the redox process.

Graphical abstractRedox effect on the static third-order nonlinear optical (NLO) properties of aromatic diimides systems with different aromatic core have been investigated with density functional theory (DFT). The results show that the studied system, especially the large aromatic core system, exhibit larger alteration of the second hyperpolarizability in reduced process and is promising to become redox-switchable NLO molecular materials.Figure optionsDownload full-size imageDownload high-quality image (116 K)Download as PowerPoint slideHighlights► The size of aromatic core can affect the γ values. ► Increasing benzenes along z axis can effectively improve the γ values. ► The reduced process causes an efficient third-order NLO switching for system 6. ► The γ values are closely related to BLA values of aromatic core for redox systems.