Electron deficient β-trisubstituted porphyrins: synthesis, structural, spectral, and electrochemical studies and their intensity-dependent third-order nonlinear optical properties.

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A series of electron-deficient β-trisubstituted 12-nitro-5,10,15,20-tetraphenyl-2,3-bis(trifluoromethyl)porphyrins, abbreviated as H2TPP(NO2)(CF3)2, and their metal complexes MTPP(NO2)(CF3)2 (where M = CoII, NiII, CuII, and ZnII) have been prepared and characterised by various spectroscopic techniques. Single crystal X-ray analysis revealed the saddle-shaped configuration of CoTPP(NO2)(CF3)2, NiTPP(NO2)(CF3)2 and CuTPP(NO2)(CF3)2 with the average deviation of the 24 core atoms from the mean porphyrin plane (Δ24) ranging from ±0.492 to ±0.499 Å and the average displacement of β-pyrrole carbons from the porphyrin mean plane (ΔCβ) ranging from ±0.926 to ±1.005 Å. H2TPP(NO2)(CF3)2 exhibited a 28 nm red shift in the B-band and a 102 nm red shift in the longest Q-band (Qx(0,0)) as compared to H2TPP. In 1H NMR, the inner imino protons of H2TPP(NO2)(CF3)2 were observed at -1.72 ppm, which is significantly downfield shifted compared to H2TPP. The first ring reduction potential of MTPP(NO2)(CF3)2 (M = 2H, CoII, NiII, CuII, and ZnII) is positively shifted by 280-620 mV compared to their corresponding MTPPs. Notably, it is observed that the synthesized MTPP(NO2)(CF3)2 porphyrins are readily reduced compared to their MTPPs. Intensity-dependent third-order nonlinear optical property studies demonstrated that the synthesized asymmetric β-substituted electron-deficient porphyrins exhibit significant two-photon absorption coefficients (β = 0.04-8.10 × 10-10 m W-1) and two-photon absorption cross-section values (σ2PA = 0.02-1.67 × 106 GM). Additionally, the materials exhibit self-defocusing negative nonlinear refraction (n2 = (-) 1.08-40.27 × 10-17 m2 W-1). The extracted NLO data suggest the potential of the investigated porphyrins for future optoelectronic and advanced material applications.