Exploring the structural and electronic properties of piperazinium bis (trifluoroacetic acid): DFT insights into optimization, spectral, NBO, NLO, Hirshfeld surface, and Fukui analysis

Organic single crystals of piperazinium bis (trifluoroacetic acid) (PTFA) was synthesized by the slow evaporation method. The centrosymmetric nature of the PTFA crystal was confirmed through single crystal XRD analysis with the P-1 space group. The molecular structure of PTFA was optimized by Density functional theory (DFT) with the B3LYP 6–311 + + G (d, p) basis set to calculated the structural parameters of the compound were compared with the experimental XRD data. The presence of various functional groups and their frequencies were confirmed through FT-IR spectral analysis, based on the potential energy distribution (PED) used for assignments and correlations of the compound’s fundamental modes. The electronic transition spectrum of the PTFA molecule was obtained via UV–Vis spectroscopy in various solvents. The analysis of HOMO & LUMO molecular orbitals indicates a significant charge transfer, while Natural Bond Orbital (NBO) analysis revealed donor–acceptor interactions. The molecular electrostatic potential (MEP) and Fukui functions, derived from Mulliken charges, identified a reactive region of the molecule. The chemical bonding was explored through Electron Localization Function (ELF) &Localized Orbital Locator (LOL) analyses and the weak interactions was identified in RDG analysis with inter & intra-fragment interactions illustrated by scatter plots. The first-order hyperpolarization calculation confirms the nonlinear optical activity of the PTFA crystal. Besides, the Hirshfeld surface analysis and 2D fingerprint maps were used for quantitative mapping of intermolecular interactions.