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

beta-Heptasubstituted porphyrins [MTPP(NO2)X6; M = 2H, NiII, CuII, and ZnII; 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 (gamma), third-order nonlinear optical susceptibility (chi 3), three-photon absorption cross-section (sigma 3), 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 sigma 3 extended in the range of (2.7-3.4) x 10-23 cm3 W-2 and (5.5-7.0) x 10-78 cm6 s2, respectively. The higher magnitude of the NLO coefficients ensures their utility in optical and photonic applications. beta-Heptasubstituted porphyrins were synthesized and their third-order nonlinear optical (NLO) properties were explored. The existence of enhanced polarization and intramolecular charge transfer are held responsible for the observed strong NLO responses.