Electron Deficient β-Trisubstituted Porphyrins: Synthesis, Structural, Spectral, and Electrochemical Studies and Their Intensity-Dependent Third-Order Nonlinear Optical Studies

A series of electron-deficient β-trisubstituted 12-nitro-5,10,15,20-tetraphenyl-2,3-bis(trifluoromethyl)porphyrin, abbreviated as H2TPP(NO2)(CF3)2 and its metal complexes MTPP(NO2)(CF3)2 (where M = CoII, NiII, CuII, and ZnII) have been prepared and characterised by various spectroscopic techniques. The 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 average deviation of the 24-core atoms from the mean porphyrin plane, (∆24) ranging from ± 0.492 to ± 0.499 Å and the average displacement of β-pyrrole carbons from the porphyrin mean plane, (∆Cβ) range was found between ± 0.926 to ± 1.005 Å. H2TPP(NO2)(CF3)2 displayed 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 280–620 mV positively shifted 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 studies demonstrated that the synthesized asymmetric β-substituted electron-deficient porphyrins exhibit a significant two-photon absorption coefficient (β = 0.04 – 8.10  10–10 m/W) and two-photon absorption cross-section values (σ_2PA = 0.02 – 1.67 x 10^6 GM). Additionally, the materials display a self-defocusing negative nonlinear refraction (n2 = (‒) 1.08 ‒ 40.27 × 10‒17 m2/W). The extracted NLO data suggests the potential of the presently investigated porphyrins as future optoelectronic and advanced materialistic applications.