The electrochemical and physicochemical properties of tetraphenylporphyrins and tetraphenylchlorins with two fused indanedione (IND) or malononitrile (MN) groups and two antipodal Br, Ph, or H β-substituents are investigated in nonaqueous media. These compounds were synthesized by oxidative fusion of free-base trans-chlorins, followed by metalation. The corresponding free-base di-fused chlorins were also isolated as intermediates and characterized for comparisons. The examined di-fused porphyrins (DFP) and di-fused chlorins (DFC) are represented as MDFP(Y) 2 (R) 2 and H 2 DFC(Y) 2 (R) 2 , where M = 2H, Cu II , Ni II , Zn II , and Co II , Y is a fused indanedione (IND) or malononitrile group (MN), and R = H, Br, or Ph. The IND-and MN-appended compounds in both series exhibit the expected two one-electron oxidations but quite different redox behavior is observed upon reduction, where the free-base IND-appended chlorins show four reversible one-electron reductions, compared to only two for the related free-base MN-appended chlorins. Although porphyrin trianions and tetraanions have been recently described for derivatives with highly electron-withdrawing and/or π-extending substituents, this seems not to be the case for the doubly fused IND-chlorins, where the first two one-electron additions are proposed to be located at the conjugated macrocycle and the last two at the fused IND groups, each of which is reduced at a different potential, consistent with the behavior expected for two equivalent and interacting redox centers. Unlike the examined chlorins, which are all stable in their electroreduced forms, the electrogenerated anionic forms of the di-fused porphyrins are all highly reactive and characterized by cyclic voltammograms having reduction peaks not only for the synthesized compounds added to solution but also for one or more new redox active species formed at the electrode surface in homogeneous chemical reactions following electron transfer. Comparisons are made between electrochemical behavior of the structurally related porphyrins and chlorins and the sites of electron transfer assigned on the basis of known electrochemical diagnostic criteria. One of the compounds, ZnDFP(MN) 2 , was also structurally characterized as having a ruffled and twisted macrocyclic conformation.

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.

Meso-tetrapyrenylporphyrin and its metal (Co[Formula: see text], Cu[Formula: see text], Ni[Formula: see text] and Zn[Formula: see text]) complexes were synthesized, characterized and studied for their spectral, electrochemical and energy transfer properties. DFT optimization was carried out to gain an insight into the interactions between the porphyrin [Formula: see text]-system and the pyrenyl substituents. The pyrenyl substituents and the porphyrin core remain essentially orthogonal to each other in both the free base and the metallated porphyrins. Redox potentials of the pyrenylporphyrins are marginally shifted as compared to their corresponding phenyl derivatives. Förster resonance energy transfer (FRET) studies were carried out in toluene for free-base pyrenylporphyrin and its Zn(II) complex. Since pyrene is a good donor, an efficient energy transfer from pyrene (D) to the porphyrin core (A) on the order of 80–85% was observed for these two compounds. It was observed that energy transfer occurs mainly via ”through-bond” (TB) interaction rather than ”through-space” (TS) interaction.

Meso-Tetraarylporphyrins having electron-withdrawing substituents viz. nitro, formyl, acyl, or bromo groups is the key precursor to expand the chemistry of β-functionalized porphyrins.1 These β-functionalized porphyrins have been utilized in nonlinear optics, anion sensing, gas storage, photodynamic therapy (PDT), and dye-sensitized solar cells (DSSC).2 Modulating the degree of π-conjugation and introducing suitable donor-acceptor substituents at β-positions result red-shifted electronic spectral features, low HOMO-LUMO gap and high ground state dipole moment which are essentials for enhanced nonlinear optical behavior. Benzoporphyrin derivatives are currently under investigation as photosensitizers for PDT.3 Herein, we synthesized unsymmetrically functionalized trisubstituted porphyrins and monobenzoporphyrins in one step and characterized by various spectroscopic techniques viz. UV-vis, fluorescence, NMR, MALDI-TOF mass spectrometry and electrochemical studies. The synthesized trisubstituted porphyrins and monobenzoporphyrins were significantly red-shifted as compared to their precursor porphyrins. Further, these porphyrins exhibited a large anodic shift in reduction and cathodic shift in oxidation potentials due to extended π-conjugation and electron-withdrawing β-substituents. In this presentation, we will present the facile synthesis, photophysical and intriguing electrochemical redox properties of π-extended porphyrins. Figure 1. Molecular structures, absorption spectral profile and cyclic voltammograms of synthesized porphyrins. References: Moura, N. M. M. et al, J. Porphyrins Phthalocyanines 15, 2011, 652-658. (a) Senge, M. O. et al, Eur. J. Org. Chem. 2011, 5797-5816. (b) Sankar, M. et al, Chem. Commun. 41, 2012, 6481-6483. (c) Kumar, R. et al, Inorg. Chem., 53, 2014, 12706-12719. (d) Higashino, T. et al, Dalton Trans. 44, 2015, 448-463. (e) Sankar, M. et al, ACS Appl. Energy Mater. 1, 2018, 2793-2801. (f) Dar, T. A. et al, Green Chem. 21, 2019, 1757-1768. (a) de-Torres, M. et al, Chem. Commun. 51, 2015, 2855-2858. (b) Zhang, X. et al, ACS Nano 12, 2018, 4630-4640. (c) Grover, N. et al, Inorg. Chem. 58, 2019, 2514-2522. Figure 1

Unsymmetrical meso-functionalized ‘push-pull’ porphyrinoid derivatives have been widely used in the areas of solar cells, photocatalysis, toxic ion sensing and nonlinear optics (NLO).1 They have been widely explored due to their ease of synthesis and facile functionalization whereas limited reports on β-substituted ‘push-pull’ π-extended porphyrinoids due to lack of synthetic methodologies. However, it is found that the latter ones exhibit unique physicochemical and electrochemical redox properties with interesting material and medicinal applications.Recently, our group has reported the facile synthesis of β-functionalized, β-meso-o-phenyl and β-β’ fused corroles, chlorins, and porphyrins with mixed substitutents pattern.2,3 The crystal structure analyses of highly substituted corroles, porphyrins and chlorins revealed quasiplanar to nonplanar saddle shape conformation. Notably, nonplanarity of the porphyrinoid core was controlled and modified by varying in size, shape, number and the electronic nature of β-substituents. These porphyrinoids exhibited highly red-shifted electronic spectra upto NIR region with dramatic decrement in HOMO-LUMO gap. In addition, the redox tunability was achieved by introducing both electron donating and withdrawing β-substituents into the tetrapyrrole skeleton which led to nonplanarity with enormous ‘cross polarization’ which has great potentiality to use in nonlinear optics (NLO). In this presentation, the facile synthesis, spectral and intriguing redox properties of these porphyrins and their potential application in materials chemistry will be discussed in detail. REFERENCES: (a) Urbani, M.; Grätzel, M. ; Nazeeruddin, M. K.; Torres, T. Chem. Rev., 2014, 114, 12330-12396. (b) Hiroto, S.; Miyake, Y.; Shinokubo, H. Chem. Rev., 2017, 117, 2910-3043. (a) Kumar, R.; Sankar, M. Inorg. Chem., 2014, 53, 12706-12719. (b) Yadav, P.; Sankar, M. Dalton Trans., 2014, 43, 14680-14688. (c) Kumar, R.; Chaudhri, N.; Sankar, M. Dalton Trans., 2015, 44, 9147-9157. (d) Kumar, R.; Chaudhary, N.; Sankar, M.; Maurya, M. R. Dalton Trans., 2015, 44, 17720-17729. (e) Grover, N.; Sankar, M.; Song Y.; Kadish, K. M. Inorg. Chem., 2016, 55, 584-597. (f) Chahal, M. K.; Sankar, M. Dalton Trans., 2016, 45, 16404-16412. (g) Sankar, M. et al. Inorg. Chem., 2017, 56, 8527-8537. (a) Chaudhri, N.; Grover, N.; Sankar, M. Inorg. Chem., 2017, 56, 424-437. (b) Chaudhri, N.; Grover, N.; Sankar, M. Inorg. Chem., 2017, 56, 11532-11545. (c) Sankar, M. et al, J. Mater. A, 201 7, 5, 6263-6276. (d) Sankar, M. et al, ACS Appl. Energy Mater., 2018, 1, 2793-2801. (e) Sankar, M. et al. Inorg. Chem., 2018, 57, 1490-1503. (f) Chaudhri, N.; Grover, N.; Sankar, M. Inorg. Chem., 2018, 57, 6658-6668. (g) Chaudhri, N.; Grover, N.; Sankar, M. Inorg. Chem., 2018, 57, 11349-11360. (h) Sankar, M. et al. Inorg. Chem., 2018, 57, 13213-13224. (i) Grover, N.; Chaudhri, N.; Sankar, M. Inorg. Chem., 2019, 58, 2514-2522. (j) Dar, T. A.; Uprety, B.; Sankar, M.; Maurya, M. R. Green Chem., 2019, 21, 1757-1768. (k) Rathi, P.; Butcher, R.; Sankar, M. Dalton Trans., 2019, 48, 15002-15011. (l) Chahal, M. K. et al. Inorg. Chem., 2019, 58, 14361-14376. (m) Chaudhri, N. et al. Inorg. Chem., 2020, 59, 1481-1495. (n) Grover, N and Sankar, M. Chem. Asian J. 2020, 15, 2192-2197.