A series of β-TCBD (1,1,4,4-tetracyano-buta-1,3diene)-appended porphyrins, M-TCBD (M = 2H, Co(II), Ni(II), Cu(II), and Zn(II)), was synthesized from 2,3-diphenylethynyl-12nitro-meso-tetraphenylporphyrin, H 2 -PE 2 , and characterized by various spectroscopic techniques and electrochemical studies. The reaction proceeds via [2 + 2] cycloaddition and retroelectrocyclization reactions of tetracyanoethylene (TCNE) with H 2 -PE 2 . The observed unusual reduction potentials in the cyclic voltammograms of the synthesized porphyrins in the range of −0.06 to −0.10 V are the consequence of the TCBD moiety present at the β-position of the porphyrin macrocycle. Notably, these porphyrins exhibited three porphyrin ring-centered reductions due to extended π-conjugation. The higher nonlinear optical response exhibited by the M-TCBD series as compared to the precursor (H 2 -PE 2 ) was attributed to the existence of intramolecular charge transfer and enhanced polarization in the M-TCBD series. The single-beam femtosecond Z-scan measurements were performed to elucidate the third-order nonlinear optical properties, and the temporal response of these porphyrin molecules was investigated using optical pump−probe spectroscopy to study the excited state absorption dynamics. Zscan measurements revealed that Co-TCBD exhibited a higher nonlinear optical response as compared to free base porphyrins. The two-photon absorption coefficient (β) and the imaginary part of third-order nonlinear optical susceptibility (χ (3) ) were obtained from the open aperture experiment, whereas the close aperture experiment delivered the magnitude and the sign of the nonlinear refractive index (n 2 ) and the real part of χ (3) . Furthermore, the femtosecond transient absorption spectroscopy revealed a faster relaxation dynamics of various absorption processes in a picosecond timescale. The excellent optical limiting threshold (1.90−2.33 × 10 15 W/m 2 ) of the synthesized porphyrins makes them good materials for laser protection and high-power laser operation.

Two new series of unsymmetrically β-functionalized porphyrins, MTPP(NO 2 )MA (1M), (MA = methyl acrylate) and MTPP(NO 2 )MB (2M) (MB = mono-benzo) (where M = 2H, Co(II), Ni(II), Cu(II) and Zn(II)), were synthesized and characterized by various spectroscopic techniques. The saddle shape conformation of ZnTPP(NO 2 )MAPy and ZnTPP(NO 2 )MB was confirmed by single-crystal X-ray analysis. Density functional theory (DFT) calculation revealed that NiTPP(NO 2 )MB has a severe nonplanar geometry possessing a high magnitude of ΔC β = ±0.727 Å and Δ24 = ±0.422 Å values among all other porphyrins. Synthesized β-substituted porphyrins exhibited red-shifted B-and Q-bands corresponding to their parent molecule due to the electron-withdrawing peripheral substituents. Notable redshift (Δλ max = 50−60 nm) in electronic spectral features and with weakintensity emission spectral features were observed for the free-base porphyrins and Zn(II) complexes compared to H 2 TPP and ZnTPP, respectively. The first-ring reduction potential of MTPP(NO 2 )MA (1M) exhibited 0.21−0.5 V anodic shift, whereas 0.18− 0.23 V anodic shift was observed in the first-ring oxidation potential compared to the corresponding MTPPs due to the presence of electron-withdrawing β-substituents at the periphery of the macrocycle. Interestingly, NiTPP(NO 2 )MA (1Ni) has shown an additional Ni II /Ni III oxidation potential observed at 2.05 V along with two ring-centered oxidations. The first-ring reduction and oxidation potentials of MTPP(NO 2 )MB (2M) have shown 0.39−0.46 and 0.19−0.27 V anodic shifts with respect to their corresponding MTPPs. The nonlinear optical (NLO) properties of all of the porphyrins were investigated, and the extracted nonlinear optical parameters revealed intense reverse-saturable absorption (RSA) behavior and the self-focusing behavior with positive nonlinear refractive index in the range of (0.19−1.75) × 10 −17 m 2 /W. Zn(II) complexes exhibited the highest two-photon absorption coefficient (β) and cross section (σ TPA ) of ∼95 × 10 −12 m/W and 19.66 × 10 4 GM, respectively, among all of the metal complexes.

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A series of “push-pull” porphyrins, MTPP(MN)(TPA)2 (M = 2H, CuII, NiII, and ZnII) having triphenylamine (TPA) and dicyanovinyl (DCN) at antipodal positions were synthesized and characterised by UV-Vis, fluorescence and...

A new series of nonplanar and unsymmetrically βfunctionalized "push−pull" copper corroles, CuTPC(CHO)R 7 [R = H, Br, Ph, Me, or 2-thienyl (Th)], were synthesized and characterized to elucidate the effect of β-functionalization and nonplanarity on the photophysical, redox, and nonlinear optical (NLO) properties on the corrole ring. The synthetic route to unsymmetrically β-octasubstituted copper corroles includes bromination of CuTPC(CHO) to get CuTPC(CHO)Br 7 in 80% yield, which was further subjected to the Pd-catalyzed Suzuki reaction. CuTPC(CHO)Br 7 exhibited a large red shift in the Soret band (Δλ max = 35−40 nm) and both the Q bands (Δλ max = 10−50 nm), as compared to CuTPC and CuTPC(CHO). CuTPC(CHO)Br 7 was 510 and 290 mV anodically shifted in the first oxidation and the first reduction compared to CuTPC owing to the strong −I effect of CHO and Br groups. Density functional theory studies revealed that all the β-octasubstituted copper corroles exhibited highly nonplanar saddle-shape conformation of the corrole ring. Very high torsional saddling was observed for CuTPC(CHO)Th 7 (79−83°) than that for CuTPC (49−53°), even larger than that for CuTPCBr 8 (67−70°). Femtosecond laser-induced third-order NLO studies from these copper corroles showed strong twophoton absorption cross-sections (0.48−6.98 × 10 4 GM) and self-focusing-type positive nonlinear refraction behavior. The observed structure-dependent two-photon absorption coefficients (β) are in the range of ∼2.7−20.9 × 10 −12 m/W, and the n 2 values are in the range of ∼0.64−6.45 × 10 −18 m 2 /W. The present results may facilitate a new window for these copper corroles in nonlinear optical devices, femtosecond optical limiters, and many other ultrafast photonic applications.