The Nonlinear Optical Characteristics of Nickel and Lanthanum Phthalocyanine Complexes Possessing Sulfonylphenoxy Functionalities

Abstract

Two novel sulfonylphenoxy-substituted lanthanum (LaPc) and nickel (NiPc) phthalocyanine complexes were synthesized and thoroughly characterized by FT-IR, 1H NMR, UV-Vis, fluorescence spectroscopy, XRD, and XPS analyses. Their third-order nonlinear optical (NLO) properties were evaluated via femtosecond laser Z-scan measurements. Structural and spectroscopic results confirmed the successful incorporation of sulfonylphenoxy groups and coordination of the respective metal centers. Comparative analysis revealed that the central metal ion strongly influenced molecular geometry, optical absorption, emission characteristics, and crystal organization. LaPc exhibited red-shifted absorption bands, enhanced fluorescence intensity, and prolonged emission lifetimes, whereas NiPc showed blue-shifted spectra and diminished quantum yields due to efficient intersystem crossing facilitated by the Ni2+ center. XRD and XPS data further substantiated these distinctions by indicating divergent coordination environments and crystal packing arrangements. The nonlinear absorption coefficient (β), nonlinear refractive index (n<inf>2</inf>), and third-order susceptibility (χ3) for both complexes were on the order of 10-11 cm/W, 10-16 cm2/W, and 10-14 esu, respectively. These results demonstrate that rational metal ion selection can effectively tailor the electronic and photophysical properties of phthalocyanines, highlighting their potential as advanced optical limiting materials for optoelectronic and photonic technologies. © 2025 Elsevier B.V.