Unsymmetrically β-Functionalized π-Extended Porphyrins: Synthesis, Spectral, Electrochemical Redox Properties, and Their Utilization as Efficient Two-Photon Absorbers

Abstract

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.

Novel phosphorus(v) tetrabenzotriazacorroles: synthesis, characterization, optical, electrochemical, and femtosecond nonlinear optical studies

“…Prominent two-photon absorption cross-sections of ∼50–500 GM were reported in the aforementioned study, which was carried out to determine their potential in optical switching applications. Song et al also extensively studied the NLO responses of various novel compounds 58–62 such as co-functionalized graphene oxide nanohybrids, self-assembled indium phthalocyanine multilayer films, novel pyrene derivatives, and neutral benzothiazole derivatives. The transient dynamics of the intra-molecular charge transfer processes were also investigated along with ultrafast NLO studies.…”

“…compounds [58][59][60][61][62] such as co-functionalized graphene oxide nanohybrids, self-assembled indium phthalocyanine multilayer films, novel pyrene derivatives, and neutral benzothiazole derivatives. The transient dynamics of the intra-molecular charge transfer processes were also investigated along with ultrafast NLO studies.…”

Regioselective 2,3-disubstituted porphyrins: synthesis, spectral, structural and electrochemical properties

“…28,[32][33][34][35][36][37] Moreover, the groups present at the porphyrin periphery (electron-withdrawing or electron-releasing), their position, oxidation state as well as the electronic nature of the central metal ion, and core structure, have a considerable effect on the redox characteristics of synthetic porphyrins. [38][39][40][41] Porphyrins show a strong absorption in the visible-light region, due to their protracted p-electron systems with considerable thermochemical stability, and thus are used as components of advanced materials. 42,43 Tetraphenylporphyrins that bear one, four and eight bromine substituents at the b-pyrrole positions have been extensively synthesized and explored on account of such facile and direct bromination at the porphyrin periphery.…”

Ethyl acetoacetate and acetylacetone appended hexabromo porphyrins: synthesis, spectral, electrochemical, and femtosecond third-order nonlinear optical studies

“…29,30 The NLO behavior of a variety of porphyrins has been investigated by our group including push-pull meso-substituted trans-A 2 BC porphyrins, where A is mesityl, B is phenothiazine ( push) and C is an o/p-nitrophenyl moiety ( pull); 8 push-pull porphyrins containing TPA-CHO/NO 2 (TPA; triphenylamine) at antipodal positions; 10 highly electron-deficient TCBDappended porphyrins; 31 highly polarizable push-pull porphyrins containing TPA and DCN (dicyanovinyl) at the antipodal position; 32 and unsymmetrically β-functionalized porphyrins appended via nitro and methyl acrylate/mono-benzo groups. 33 To date, non-planar electron-deficient hexa-bromo porphyrins bearing one acac/EAA moiety at the β-position remain unexplored towards NLO applications. Therefore, we synthesized MTPP[EAA]Br 6 and MTPP[acac]Br 6 (M = 2H, Cu(II), and Ni(II)) using a Michael addition reaction (Michael donor: EAA/acac) and characterized them using various photophysical, electrochemical and computational techniques; and finally, thirdorder NLO properties were investigated using a single-beam femtosecond Z-scan technique (investigated macrocycles are displayed in Chart 1).…”