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

β-Heptasubstituted porphyrins [MTPP(NO ₂ )X ₆ ; 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 ( χ ³ ), three-photon absorption cross-section ( σ ₃ ), and nonlinear refractive index ( n ₂ ) have been determined from theoretical fits with experimental results. The sign and magnitude of the nonlinear refractive index ( n ₂ ) 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 σ ₃ extended in the range of (2.7-3.4) × 10 ^-23 cm ³ W ^-2 and (5.5-7.0) × 10 ^-78 cm ⁶ s ² , respectively. The higher magnitude of the NLO coefficients ensures their utility in optical and photonic applications.