Imidazolium versus phenylalaninium hybrid salts: supramolecular control of electronic, nonlinear optical and bioactive properties.

Two new amino-acid-based hybrid salts, l-phenylalaninium chloride (1) and l-histidinium iodide (2), were synthesized and comprehensively characterized to elucidate how cation identity, halide nature, and supramolecular architecture govern their optical, electronic, and biological properties. Single-crystal X-ray diffraction revealed that both compounds crystallize in the non-centrosymmetric P212121 space group but exhibit distinct packing motifs: a compact chloride-stabilized network in (1) and a more open, highly polarized iodide-based framework in (2). DFT calculations show that compound (2) possesses a significantly reduced HOMO-LUMO band gap, higher molecular softness, and enhanced intramolecular charge transfer, leading to a first hyperpolarizability nearly three times larger than that of (1). FT-IR and RDG analyses confirm stronger charge-assisted N-H⋯I interactions in (2), consistent with its superior electronic polarization. Biological assays further demonstrate that compound (2) exhibits markedly enhanced antioxidant and antibacterial activities, attributed to its imidazolium-based charge distribution and iodide polarizability. Together, these findings establish clear structure-property relationships and highlight the effectiveness of combining heterocyclic amino acids with highly polarizable halides to design multifunctional organic-inorganic materials with promising NLO and bioactive potential.