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.