Third-order nonlinear optical coefficients (n2, β, χ3) determined by Z-scan for MgSO4-doped 4-methoxy–4′-nitrostilbene hybrid crystal: Structural, spectroscopic, and photonic properties

Abstract

A new organic–inorganic hybrid single crystal of magnesium sulfate-doped 4-methoxy–4′-nitrostilbene has been prepared successfully by following a slow-evaporation solution growth method and thoroughly characterized with structural, spectroscopic, theoretical, and laser-induced optical investigations. In-depth quantum-chemical optimization (Hartree–Fock/time-dependent-self consistent field/Stuttgart/Dresden Electronic Structure Package) unravels non-centrosymmetric orthorhombic packing with field-induced distortions, eminent π-electron delocalization, and strong donor–π–acceptor (D–π–A) interactions; requirements for effective nonlinear optical response. XRD indicates high crystallinity with preferred (110) orientation, and morphological and boundary analyses indicate anisotropic growth and inter-chain bonding, facilitating directional charge transport as well as optical birefringence. Special emphasis is placed on measuring the third-order nonlinear optical coefficients of the hybrid crystal using the Z-scan technique. In a very concentrated 1.3 GW cm−2 beam at 532 nm, the material has a nonlinear refractive index n2 = 3.143 × 10−10 cm2 W−1, nonlinear absorption coefficient β = 6.51 × 10−4 cm W−1 (reverse saturable/two-photon absorption), and third-order nonlinear susceptibility χ(3) = 8.814 × 10−6 esu, all of which are higher than reference crystals, such as potassium dihydrogen phosphate. They are grounded in high polarizability and hyperpolarizability computed from nonbonding molecular orbital and molecular electrostatic potential (βtot = 12 120 a.u., αtot ≈ 29 012 120 a.u., μ ≈ 16.9 D) that indicate strong intramolecular charge transfer and electron-cloud deformation by the dopant. Complementary measurements show a broad optical bandgap (3.56 eV), large laser damage threshold (≈12.2 J cm−2), and low optical-limiting threshold (≈5.8 × 103 W cm−2), indicative of the stability of the crystal in high-intensity light fields. Vibrational assignments, nuclear magnetic resonance predictions, and frontier orbital analyses also witness structural stability and the nonlinear optical response inferred from the Z-scan.