Exploring the optoelectronic and third-order nonlinear optical susceptibility of cross-shaped molecules: insights from molecule to material level.

In the present investigation, we use a dual computational approach (at single molecular and solid-state levels) to explore the optoelectronic and nonlinear optical (NLO) properties of cross-shaped derivatives. The solid-state electronic band structures of the compounds 1-3 (the derivatives of tetracarboxylic acid in cross-shaped having the core of benzene (1), pyrazinoquinoxaline (2), and tetrathiafulvalene (3)) are calculated. The calculated band gaps for compounds 1-2 are found to be direct bad gaps and compound 3 to be indirect bad gap with energy gaps of 2.749, 1.765, and 0.875 eV, respectively. The important optical properties including refractive index, absorption coefficients, loss functions, and extinction coefficient of these semiconductors are calculated at bulk level to seek their potential applications as efficient optoelectronic materials. Additionally, we use the Lorentz approximation to calculate the third-order NLO susceptibilities of compounds 1-3 using the molecular hyperpolarizability and solid-state parameters. The calculated third-order NLO susceptibilities of compounds 1-3 are found to be 6.92 × 10-12, 64.0 × 10-12, and 26.3 × 10-12 esu, respectively. Thus, the present study not only provides a way to connect the calculated third-order molecular NLO polarizability to NLO susceptibilities for compounds 1-3 through Lorentz approximation but also highlights the importance of central core modifications on their NLO susceptibilities.