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<p>A novel KMnO₄-coordinated L-arginine complex was synthesized and comprehensively investigated through an interdisciplinary approach encompassing crystal-growth modeling, theoretical calculations, spectroscopic characterization, and nonlinear optical (NLO) analysis. Incorporation of KMnO₄ into the L-arginine matrix induces pronounced lattice distortion, manifested by anisotropic crystal growth along the a-, b-, and particularly the c-axes. XRD reveals an orthorhombic structure with a nearly distorted <i>P2₁/c</i> space group, sharp diffraction peaks, and high crystallinity. Vibrational modes analyses confirm non-centrosymmetric geometry and active functional modes; fundamental requirements for NLO activity. Theoretical calculations involving geometry optimization, Mulliken charge distribution, and molecular electrostatic potential (MEP) mapping indicate extensive charge redistribution and strong metal–ligand field interactions. Optical studies disclose a direct band gap of 3.67&#xa0;eV, high birefringence (Δn = 0.20), and 1.86 (2.85&#xa0;mm) optical transmittance, establishing the complex as a wide-band-gap material resistant to visible-region carrier absorption, suitable for UV-active and high-power photonic applications. The measured third-order nonlinear optical susceptibility (χ³ = 4.82 × 10⁻⁷ esu) demonstrates a strong third-order response arising from efficient intramolecular charge transfer within the Mn–O–C–N coordination framework. Correspondingly, the nonlinear refractive index (n₂ = 1.35 × 10⁻⁸ cm² W⁻¹) is attributed to electronic cloud distortion and localized defect-state interactions, yielding pronounced self-focusing behavior. The nonlinear absorption coefficient (β = 5.47 × 10⁻⁵ cm W⁻¹) signifies reverse-saturable absorption (RSA) driven by excited-state processes, advantageous for optical-limiting and photonic-switching functions. HOMO–LUMO transitions (H → L ≈ 0.625&#xa0;eV) and electronic spectra support effective ligand-to-metal charge transfer and band-gap modulation, while NBO and perturbation analyses reveal intramolecular charge delocalization. Collectively, these results affirm that KMnO₄-doped L-arginine crystal combines broad optical transparency with pronounced third-order nonlinearity, establishing it as a promising candidate for next-generation photonic and optoelectronic devices.</p>

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Theoretical modeling, surface morphology, spectroscopic characterization, and laser-induced nonlinear optical evaluation of KMnO₄-coordinated L-arginine crystalline complexes

  • 期刊论文

  • 发表日期：

    2025年12月15日

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  • T. Sathiyapriya,
  • S. Ramalingam,
  • A. Samuel John Peter

摘要

A novel KMnO₄-coordinated L-arginine complex was synthesized and comprehensively investigated through an interdisciplinary approach encompassing crystal-growth modeling, theoretical calculations, spectroscopic characterization, and nonlinear optical (NLO) analysis. Incorporation of KMnO₄ into the L-arginine matrix induces pronounced lattice distortion, manifested by anisotropic crystal growth along the a-, b-, and particularly the c-axes. XRD reveals an orthorhombic structure with a nearly distorted P2₁/c space group, sharp diffraction peaks, and high crystallinity. Vibrational modes analyses confirm non-centrosymmetric geometry and active functional modes; fundamental requirements for NLO activity. Theoretical calculations involving geometry optimization, Mulliken charge distribution, and molecular electrostatic potential (MEP) mapping indicate extensive charge redistribution and strong metal–ligand field interactions. Optical studies disclose a direct band gap of 3.67 eV, high birefringence (Δn = 0.20), and 1.86 (2.85 mm) optical transmittance, establishing the complex as a wide-band-gap material resistant to visible-region carrier absorption, suitable for UV-active and high-power photonic applications. The measured third-order nonlinear optical susceptibility (χ³ = 4.82 × 10⁻⁷ esu) demonstrates a strong third-order response arising from efficient intramolecular charge transfer within the Mn–O–C–N coordination framework. Correspondingly, the nonlinear refractive index (n₂ = 1.35 × 10⁻⁸ cm² W⁻¹) is attributed to electronic cloud distortion and localized defect-state interactions, yielding pronounced self-focusing behavior. The nonlinear absorption coefficient (β = 5.47 × 10⁻⁵ cm W⁻¹) signifies reverse-saturable absorption (RSA) driven by excited-state processes, advantageous for optical-limiting and photonic-switching functions. HOMO–LUMO transitions (H → L ≈ 0.625 eV) and electronic spectra support effective ligand-to-metal charge transfer and band-gap modulation, while NBO and perturbation analyses reveal intramolecular charge delocalization. Collectively, these results affirm that KMnO₄-doped L-arginine crystal combines broad optical transparency with pronounced third-order nonlinearity, establishing it as a promising candidate for next-generation photonic and optoelectronic devices.