Isatin-indole hybrid molecule: A simple synthesis to design an efficient NLO material

The isatin-indole hybrid molecule, referred to as molecule 5, (Z)-3-((4-((4-((E)-((1H-indol-3-yl)methylene) amino)phenyl)sulfonyl)phenyl)imino)indolin-2-one (C29H20N4O3S), is synthesized through a straightforward method and its structure confirmed using (1H, 13C) NMR, IR, Mass, and UV-vis. spectroscopic techniques. The molecular arrangement of molecule 5 is determined by employing Density Functional Theory (DFT) with the B3LYP functional to acquire its optimized geometry. Various theoretical parameters, including dipole moment (Debye), polarizability (alpha) in esu, hyperpolarizability (beta) in esu, EHOMO (eV), ELUMO (eV), and Egap (eV), were computed using the DFT approach. These computed physiochemical attributes underscore the capability of both isatin and indole molecules to stabilize the optimized geometry of molecule 5 via interactions across the sulfonyl group. The outcomes indicated that hybrid molecule 5 exhibited superior nonlinear optical (NLO) efficiency, characterized by a small HOMO-LUMO energy gap and a substantial hyperpolarizability. Furthermore, an indepth exploration of the theoretical UV-vis. spectrum using TD-DFT calculations provided detailed assignments for electronic transitions, demonstrating a noteworthy consistency with the experimental spectrum. This collective information reinforces the potential of the hybrid molecule 5 as an efficient candidate for optical and NLO applications.