Atom‐in‐Molecule Analysis, Density Function Theory Research, Spectroscopy, Charge Transfer, and (Static, Dynamic) Nonlinear Optical Effects of (Z)4,4 ^′ ‐Bis[‐3‐N‐Ethyl‐2‐N’‐(Phenylimino) Thiazolidin‐4‐One] Methane

-bis[-3-N-ethyl-2-N'-(phenylimino) thiazolidin-4-one] methane (2-EPTh). Fourier transform infrared (FT-IR), UV-vis, 1H, and 13C nuclear magnetic resonance techniques characterized the molecule's structure. UV-vis results indicated that the molecule can absorb light in the wavelength range of 200-375 nm. Density functional theory calculations have been performed using Becke-Yang-part function functional with the basis set 6-311G (d, p) to support the experimental results. Theoretical and empirical findings are approximately similar. In addition, the molecular electrostatic potential (ESP) of 2-EPTh was simulated to identify favorable sites for electrophilic and nucleophilic reactions. Moreover, the frontier orbital energy gap was thoroughly studied. Furthermore, atom-in-molecules theory examines covalent bonding and intermolecular interactions. The ESP and dipole moment were also determined using experimental X-ray diffraction data. Ultimately, the study determined that the title compound is a suitable candidate for nonlinear optical applications, as demonstrated by its electric dipole moment (μ), polarizability (α), and first hyperpolarizability (β). More specifically, its second hyperpolarizability response has shown promising results for the dimer of our molecule, in both static and dynamic dependent-frequency (λ = 532 nm) states, and in the gaseous environment as well as in the presence of solvent.