Third-order nonlinear optical properties of highly electron deficient, nonplanar push–pull porphyrins: β-nitro-hexa-substituted porphyrins bearing bromo, phenyl, and phenylethynyl groups

Abstract

β-Heptasubstituted porphyrins [MTPP(NO₂)X₆; M = 2H, Ni^II, Cu^II, and Zn^II; X = Br, Ph, and PE] were synthesized and their third-order nonlinear optical (NLO) properties explored using the single-beam Z-scan technique with femtosecond, MHz pulses in the visible range. The three-photon absorption (γ), third-order nonlinear optical susceptibility (χ³), three-photon absorption cross-section (σ₃), and nonlinear refractive index (n₂) have been determined from theoretical fits with experimental results. The sign and magnitude of the nonlinear refractive index (n₂) have been obtained from the closed-aperture experiment while the three-photon absorption coefficient and three-photon absorption cross-section were determined from the open-aperture experiment. The magnitudes of the 3PA and σ₃ extended in the range of (2.7–3.4) × 10⁻²³ cm³ W⁻² and (5.5–7.0) × 10⁻⁷⁸ cm⁶ s², respectively. The higher magnitude of the NLO coefficients ensures their utility in optical and photonic applications.