Two new families of porphyrins with mixed substituent pattern, viz. 2-nitro-12,13-disubstituted-meso-tetraphenylporphyrins (H2TPP(NO2)X2, X = Ph, phenylethynyl (PE), 2-thienyl (Th), Br, and CN) and 2-nitro-7,8,12,13,17,18-hexasubstituted-meso-tetraphenylporphyrins (H2TPP(NO2)X6, X = Br, Ph, PE, and Th), and their metal (Co(II), Ni(II), Cu(II), and Zn(II)) complexes have been synthesized and characterized. H2TPP(NO2)X6 exhibited remarkable red shift in the Soret band (45-70 nm) and longest wavelength band, Qx(0,0) (65-90 nm), as compared to H2TPP(NO2). Single-crystal structures of MTPP(NO2)X2 (M = Zn(II) and Ni(II); X = Br, Ph, and PE) showed quasi-planar conformation, whereas H2TPP(NO2)Th2 and NiTPP(NO2)Br6 exhibited moderate and highly nonplanar saddle-shape conformations, respectively. Further, DFT fully optimized geometries of H2TPP(NO2)X2 and H2TPP(NO2)X6 revealed moderate and severe saddle-shape nonplanar conformations, respectively. The imino proton resonances of H2TPP(NO2)X6 are significantly downfield shifted (Δδ = 1.10-1.80 ppm) relative to H2TPP(NO2). Mixed substituted highly nonplanar porphyrins exhibited higher protonation and deprotonation constants relative to H2TPPX8 (X = Cl and Br). The redox tunability was achieved by introducing electron donor (Ph and Th) and acceptor (PE, Br, and CN) groups on the MTPP(NO2) backbone. The unusual variation in the spectral and electrochemical redox properties of mixed substituted porphyrins are interpreted in terms of both an inductive and a resonance interaction of substituents on the porphyrin π-system as well as nonplanarity of the macrocycle.

A series of cobalt porphyrins with π-extending or highly electron-withdrawing β-pyrrole substituents were investigated as to their electrochemistry, spectroscopic properties, and reactivity after electroreduction or electroxidation in nonaqueous media. Each porphyrin, represented as PorCo (where Por = TPP(NO)Y or TPP(NO)Y and Y = phenyl, phenylethynyl, Br, or CN) was shown to undergo multiple redox reactions involving the conjugated π-ring system or central metal ion which could exist in a Co(III), Co(II), or Co(I) oxidation state under the application of an applied oxidizing or reducing potential. Thermodynamic half-wave potentials for the stepwise conversion between each oxidation state of [PorCo] (where n ranged from +3 to -3) were measured by cyclic voltammetry and analyzed as a function of the compound structure and properties of the electrochemical solvent. UV-visible spectra were obtained for each oxidized or reduced porphyrin in up to six different oxidation states ranging from [PorCo] to [PorCo] and analyzed as a function of the compound structure and utilized electrochemical solvent. Chemically or electrochemically generated Co(I) porphyrins are known to be highly reactive in solutions containing alkyl or aryl halides, and this property was utilized to in situ generate a new series of methyl carbon-bonded cobalt(III) porphyrins with the same π-extending or highly electron-withdrawing substituents as the initial Co(II) derivatives. The electrosynthesized carbon-bonded Co(III) porphyrins were then characterized as to their own electrochemical and spectroscopic properties after the addition of one, two, or three electrons in nonaqueous media.

Five cost-effective porphyrin based sensitizers with various donor groups (bisthiophene, N,N-dimethylaminophenyl, triphenylamine, carbazole and phenothiazine) and meso-dimesityl as auxiliary groups have been synthesized through the shortest possible synthetic route for the practical commercialization of these dyes. trans-A2BC porphyrin dyes show power conversion efficiencies (η) ranging from 5.3% to 7.11% under 1 sun illumination and highly depend on donor strength of appended moiety. Our molecular design incorporates trans-10,20-dimesityl groups, which prevents the π–π aggregation between the porphyrin units onto the TiO2 surface. The porphyrin dye (RA-200-Zn) bearing phenothiazine as donor unveils the highest photon-to-current conversion efficiency (PCE) of 7.1% and showed butterfly conformation, which can restrict the intermolecular aggregation. Further, this dye shows a broader absorption on TiO2 surface and significantly increased IPCE values in visible region as compared to the other dyes, which assured better light harvesting ability with high short-circuit current density (J sc) of 14.2 mA cm–2.

The first examples for the facile, reversible, and stepwise electrogeneration of triply ring-reduced porphyrin macrocycles are presented. The investigated compounds are represented as MTPP(NO)(PE), MTTP(PE), NiTPP(NO)(Ph), and MTPP(CN), where TTP and TPP are the dianions of tetratolylporphyrin and tetraphenylporphyrin, respectively, NO, phenylethynyl (PE), and CN are substituents at the β-pyrrole positions of the macrocycle, and M = Cu, Ni, Zn, Co, or 2H. Each porphyrin undergoes three or four reductions within the negative potential limit of the electrochemical solvent. The UV-visible spectra of the first three reduction products were characterized by means of thin-layer UV-vis spectroelectrochemistry, and the generation of multianionic porphyrins is interpreted in terms of extensive stabilization of the LUMOs due to the electron-withdrawing and/or extended π-conjugation of the β-substituents.

We have synthesized 2,3,7,8,12,13,17,18-octachloro-meso-tetraphenylporphyrinatooxidovanadium(iv) (VOTPPCl8) and characterized by various spectroscopic (UV-Vis, IR and EPR) techniques, MALDI-TOF mass spectrometry and elemental analysis. The DFT optimized structure of VOTPPCl8 in CH3CN exhibited a highly nonplanar saddle shape conformation of the porphyrin macrocycle. The cyclic voltammogram of VOTPPCl8 showed a 500 mV anodic shift in the first ring reduction potential and 220 mV in the first ring oxidation potential compared to VOTPP indicating the electron deficient nature of the porphyrin π-system and further proving the existence of a nonplanar conformation of the macrocycle in solution. Further, VOTPPCl8 exhibited very high thermal stability till 390 °C as indicated in its thermogram. The oxidation state of the metal ion (V(IV)) was confirmed by EPR spectroscopy and VOTPPCl8 exhibited an axial spectrum which corresponds to the axially compressed dxy(1) configuration. VOTPPCl8 was utilised for the selective epoxidation of various olefins in good yields with very high TOF numbers (6566-9650 h(-1)) in the presence of H2O2 as an oxidant and NaHCO3 as a promoter in a CH3CN/H2O mixture. The oxidoperoxidovanadium(v) species is expected to be the intermediate during the catalytic reaction which is probed by (51)V NMR spectroscopy and MALDI-TOF mass analysis. Notably, VOTPPCl8 is stable after the catalytic reaction and doesn't form a μ-oxo dimer due to the highly electron deficient nonplanar porphyrin core and can be reused for several cycles.