Porphyrin Core Research Articles

All are aromatic: A 3D globally aromatic cage containing five types of 2D aromatic macrocycles

All are aromatic: A 3D globally aromatic cage containing five types of 2D aromatic macrocycles

Photophysical study and in vitro approach against Leishmania panamensis of dicloro-5,10,15,20-tetrakis(4-bromophenyl)porphyrinato Sn(IV)

Background:Photodynamic therapy activity against different biological systems has been reported for porphyrins. Porphyrin modifications through peripheral groups and/or by metal insertion inside the ring are main alternatives for the improvement of its photo-physical properties. In this study, we synthesized and characterized 5,10,15,20-tetrakis(4-bromophenyl)porphyrin and the dicloro-5,10,15,20-tetrakis(4-bromophenyl)porphyrinato Sn(IV).Methods:Metal-free porphyrin was synthesized using the Alder method, while the Sn(IV)-porphyrin complex was prepared by combining metal-free porphyrin with stannous chloride in DMF; the reaction yields were 47% and 64% respectively. Metal-free porphyrin was characterized by UV-Vis, FT-IR, ESI-mass spectrometry and13C-NMR. Additionally, the Sn(IV) -porphyrin complex was characterized using UV-Vis and FT-IR. Cyclic voltammetry tests in four different solvents. The fluorescence quantum yield (Φf) was measured using fluorescein as a standard, the singlet oxygen quantum yield (ΦD) was estimated using the standard 5,10,15,20-(tetraphenyl)porphyrin (H2TPP) and the quencher of singlet oxygen 1,3-diphenylisobenzofuran (DPBF).Results:UV-Vis assay showed typical Q and Soret bands for porphyrin and its metallo-porphyrin complex. Compounds showed photoluminescence at the visible range of electromagnetic spectrum. The inclusion of the metal in the porphyrin core changed the Φffrom 0.15 to 0.05 and the ΦDincreased from 0.55 to 0.59. Finally, the effect of the compounds on the viability ofL. panamensiswas evaluated by means of the MTT test. The results showed that both compounds decreased the viability of the parasite; this inhibitory activity was greater under light irradiation; the porphyrin compound had IC50of 16.5 μM and the Sn(IV)-porphyrin complex had IC50of 19.2 μM.Conclusion:The compounds were synthesized efficiently, their characterization was carried out by different spectroscopy techniques and their own signals were evidenced for both structures, both compounds decreased the cell viability ofL. panamensis.

Comparing Cyanophenyl and Pyridyl Ligands in the Formation of Porphyrin-Based Metal-Organic Coordination Networks.

In recent studies, porphyrin derivatives have been frequently used as building blocks for the fabrication of metal–organic coordination networks (MOCNs) on metal surfaces under ultrahigh vacuum conditions (UHV). The porphyrin core can host a variety of 3d transition metals, which are usually incorporated in solution. However, the replacement of a pre-existing metal atom in the porphyrin core by a different metallic species has been rarely reported under UHV. Herein, we studied the influence of cyanophenyl and pyridyl functional endgroups in the self-assembly of structurally different porphyrin-based MOCNs by the deposition of Fe atoms on tetracyanophenyl (Co-TCNPP) and tetrapyridyl-functionalized (Zn-TPPyP) porphyrins on Au(111) by means of scanning tunneling microscopy (STM). A comparative analysis of the influence of the cyano and pyridyl endgroups on the formation of different in-plane coordination motifs is performed. Each porphyrin derivative formed two structurally different Fe-coordinated MOCNs stabilized by three- and fourfold in-plane coordination nodes, respectively. Interestingly, the codeposited Fe atoms did not only bind to the functional endgroups but also reacted with the porphyrin core of the Zn-substituted porphyrin (Zn-TPyP), i.e., an atom exchange reaction took place in the porphyrin core where the codeposited Fe atoms replaced the Zn atoms. This was evidenced by the appearance of molecules with an enhanced (centered) STM contrast compared with the appearance of Zn-TPyP, which suggested the formation of a new molecular species, i.e., Fe-TPPyP. Furthermore, the porphyrin core of the Co-substituted porphyrin (Co-TCNPP) displayed an off-centered STM contrast after the deposition of Fe atoms, which was attributed to the binding of the Fe atoms on the top site of the Co-substituted porphyrin core. In summary, the deposition of metal atoms onto organic layers can steer the formation of structurally different MOCNs and may replace pre-existing metal atoms contained in the porphyrin core.

Thermally Induced Synthesis of Anthracene-, Pyrene- and Naphthalene-Fused Porphyrins.

The synthesis of π‐extended porphyrins containing anthracenyl moieties still represents an important challenge. Here, we report on the synthesis of a series of unsubstituted naphthyl‐, pyrenyl‐ and anthracenyl‐fused zinc porphyrin derivatives. To this aim, meso‐substitued porphyrins are synthesized and the fusion of the PAHs (Polycyclic Aromatic Hydrocarbon) on the β‐positions are performed through thermally induced dehydro‐aromatization. The fused zinc‐porphyrin derivatives are fully characterized and their optical absorption and photoluminescence properties are reported. We also demonstrate that zinc can be removed from the porphyrin core, giving rise to pure C, H, N materials. This work constitutes the first step towards the synthesis of the fully‐fused tetra‐anthracenylporphyrin.

Facile synthesis of antipodal β-arylaminodibromoporphyrins through Buchwald-Hartwig C-N coupling reaction and exploring their spectral and electrochemical redox properties

A new family of antipodal β-arylaminodibromoporphyrins was synthesized through a Buchwald-Hartwing C-N coupling reaction and characterized as to its spectroscopic and electrochemical properties. The investigated compounds are represented as (NHR)Br2TPPM where M = 2H, Cu(II) or Zn(II), (NHR)Br2TPP is the dianion of β-arylaminodibromotetraphenylporphyrin and R is one of the five different aryl groups: Ph, m,m-Me2Ph, NPH = 1-naphthyl, p-CNPh, p-NO2Ph. The yield of desired arylaminoporphyrin depends upon the equivalents of arylamine utilized in the reaction and the electron-donating or electron-withdrawing nature of the R group present on the phenyl ring of the β-arylamino moiety. The Soret bands of these porphyrins are broader and red-shifted as compared to the related tetraphenylporphyrin derivatives, TPPM, whereas their Q bands are intense due to push-pull effects. The emission bands of the free base and Zn(II) derivatives are weak, broad and red-shifted (Δλem = 17-60 nm) as compared to their corresponding TPPM derivatives (M = 2H and Zn) due to the cross-polarized push-pull β-substituents and the heavy atom effect of the two bromo substituents. The (NHR)Br2TPPM complexes exhibit characteristic split NMR signals due to the unsymmetrical β-substitution. The DFT optimized structures indicate a moderate nonplanar porphyrin core, with the Cu(II) arylaminoporphyrins having the largest ∆24 values (average displacement of 24 atoms of macrocyclic core) of 0.595-0.622 Å. The redox properties are also influenced by the electronic nature of the arylamino group with the measured half-wave potentials for reduction being positively shifted by 0.09-0.21 V as compared to the parent TPPM complexes whereas marginal shifts were observed for oxidation processes with respect to the TPPM derivatives. This leads to a 0.14-0.20 V decrease in the electrochemically measured HOMO-LUMO gap for the β-arylaminodibromoporphyrins as compared to the corresponding TPPM analogues.

Synthesis, X-ray molecular structure and QTAIM and NCI-RDG theoretic studies of a new cadmium (II) (4′4 diaminodiphenylmethane) (meso-arylporphyrin) coordination compound

In this study, a new five-coordinated cadmium porphyrin complex axially ligated with 4,4′-diaminodiphenylmethane (4,4′-mda) with the formula [Cd(TClPP)(4,4′-mda)]•CHCl3•(4,4′-mda)•2H2O (complex (1)) where TClPP is the meso-tetra(para-chlorophenyl)porphyrinate was prepared and characterized by FT-IR,1H NMR, and UV/Vis spectroscopy. The crystal structure was determined using single crystal X-ray diffraction. This complex crystallizes in the monoclinic crystal system with the space group P-1. The coordination sphere around the cadmium center is shown as a distorted square pyramidal coordination environment and the porphyrin core presents a dome-type deformation due to the large size of the central cadmium(II) ion. The crystal lattice of (1) is mainly stabilized by classic and non-conventional hydrogen bonds as indicated by the experimental data explored by the PLATON program. To obtain an insight into the physical nature of these intermolecular bonds, we extensively used Bader's quantum theory of atoms-in-molecules (QTAIM). This analysis proved that the coordinated 4,4′-mda (ligand I) stabilizes the structure of (1) by the formation of Van der Waals (VdW) type interactions. Additionally, the non-covalent interaction via the reduced density gradient (NCI-RDG) analysis established nicely the presence of such intermolecular interactions type hydrogen bonding interactions between ligands I and II, from one side, and (iii) hydrogen bonding and Van der Waal interactions, from the other side, with involving [Cd(TClPP)(4,4′-mda)], ligand I and II and the neighboring [Cd(TClPP)(4,4′-mda)] molecules.

Photoinduced Charge Transfer with a Small Driving Force Facilitated by Exciplex-like Complex Formation in Metal-Organic Frameworks.

Photoinduced charge transfer (PCT) is a key step in the light-harvesting (LH) process producing the redox equivalents for energy conversion. However, like traditional macromolecular donor-acceptor assemblies, most MOF-derived LH systems are designed with a large ΔG0 to drive PCT. To emulate the functionality of the reaction center of the natural LH complex that drives PCT within a pair of identical chromophores producing charge carriers with maximum potentials, we prepared two electronically diverse carboxy-terminated zinc porphyrins, BFBP(Zn)-COOH and TFP(Zn)-COOH, and installed them into the hexagonal pores of NU-1000 via solvent-assisted ligand incorporation (SALI), resulting in BFBP(Zn)@NU-1000 and TFP(Zn)@NU-1000 compositions. Varying the number of trifluoromethyl groups at the porphyrin core, we tuned the ground-state redox potentials of the porphyrins within ca. 0.1 V relative to that of NU-1000, defining a small ΔG0 for PCT. For BFBP(Zn)@NU-1000, the relative ground- and excited-state redox potentials of the components facilitate an energy transfer (EnT) from NU-1000* to BFBP(Zn), forming BFBP(Zn)S1* which entails a long-lived charge-separated complex formed through an exciplex-like [BFBP(Zn)S1*-TBAPy] intermediate. Various time-resolved spectroscopic data suggest that EnT from NU-1000* may not involve a fast Förster-like resonance energy transfer (FRET) but rather through a slow [NU-1000*-BFBP(Zn)] intermediate formation. In contrast, TFP(Zn)@NU-1000 displays an efficient EnT from NU-1000* to [TFP(Zn)-TBAPy], a complex that formed at the ground state through electronic interaction, and thereon showed the excited-state feature of [TFP(Zn)-TBAPy]*. The results will help to develop synthetic LHC systems that can produce long-lived photogenerated charge carriers with high potentials, i.e., high open-circuit voltage in photoelectrochemical setups.

Novel meso‐substituted ferrocene‐appended porphyrins: Synthesis, characterization, and electrochemical evaluation

This paper focuses on the synthesis of the novel ferrocene‐appended porphyrin architectures and their zinc metal complexes. Tetraferrocenylporphyrins are a class of organometallic compounds where the porphyrin core is functionalized with a ferrocenyl unit at each of the four meso positions. Tetraferrocenylporphyrin derivatives were synthesized via a direct tetramerization reaction between some ferrocene carboxaldehyde derivatives and pyrrole in the presence of BF3·Et2O as an efficient catalyst. Moreover, a metalation reaction between tetraferrocenylporphyrin derivatives and zinc acetate was applied in the synthesis of related zinc complexes. The structures of the new organometallic compounds were confirmed by Fourier transform infrared spectroscopy (FT‐IR), 1H NMR, 13C NMR, UV–vis, and CHNS analyses. The redox‐active properties of the synthesized compounds were characterized by cyclic voltammetry (CV) analysis.

Facilitated interfacial charge separation using triphenylamine-zinc porphyrin dyad-sensitized TiO2 nanoparticles for photocatalysis

Three triphenylamine (TPA) substituted dichromophoric zinc porphyrins XZP1–3 and a single zinc porphyrin ZP1 have been rationally designed to construct dye-sensitized TiO2 nanoparticles to explore the feasibility of dichromophoric dye design for photocatalysis. TPA, N,N-diphenyl-(1,1′-biphenyl)− 4-amine and a carbazole-diphenylaniline derivative are attached to the meso-position of porphyrin core as the second chromophore. The electronic structure of the porphyrins is studied by density functional theory (DFT) calculations and the dye-sensitized composites are investigated using couples of spectral and electrochemical techniques. XZP2/TiO2 exhibits the smallest charge transfer resistance and the longest electron lifetime among the investigated composites. The same catalyst performs the highest efficiency in photodegradation of both acid black (AB1) and tetracycline (TC) polluted water samples. Electronic paramagnetic resonance and radical quenching experiments reveal that the priority reactive species are superoxide radicals (•O2−) and holes (h+), suggesting the efficient charge separation at the porphyrin-sensitized TiO2 interface. This work demonstrates the facilitated interfacial charge separation using dichromophoric dye-sensitized semiconductor particles for photodegradation and, the insights should aid in dyad design for photocatalysis application.

Core-modified porphyrins: novel building blocks in chemistry

Abstract Various (metallo)porphyrins and related compounds have been intensively investigated by different research groups due to their extremely important role in living organisms along with their versatile applications in technology. The design of novel porphyrinoids by core-modification, or substitution of pyrrole nitrogens, with the elements of other groups of the Periodic Table has been considered as a highly promising methodology for tuning structures and properties of porphyrinoids and thus opening new possible applications for them. Much effort has been given to the modifications of the porphyrin core with elements of the main groups, namely O, S, Se (chalcogens), and the heavier congener of nitrogen, phosphorus. In general, the porphyrin core modification by replacing nitrogens with heteroatoms is a promising and effective strategy for obtaining new compounds with unusual structures and properties (optical, electrochemical, coordinating, etc.) as well as reactivity. These novel molecules can also be employed as promising building or construction blocks in various applications in the nanotechnology area.

Water-Soluble Non-Ionic PEGylated Porphyrins: A Versatile Category of Dyes for Basic Science and Applications.

This review arises from the need to rationalize the huge amount of information on the structural and spectroscopic properties of a peculiar class of porphyrin derivatives-the non-ionic PEGylated porphyrins-collected during almost two decades of research. The lack of charged groups in the molecular architecture of these porphyrin derivatives is the leitmotif of the work and plays an outstanding role in highlighting those interactions between porphyrins, or between porphyrins and target molecules (e.g., hydrophobic-, hydrogen bond related-, and coordination-interactions, to name just a few) that are often masked by stronger electrostatic contributions. In addition, it is exactly these weaker interactions between porphyrins that make the aggregated forms more prone to couple efficiently with external perturbative fields like weak hydrodynamic vortexes or temperature gradients. In the absence of charge, solubility in water is very often achieved by covalent functionalization of the porphyrin ring with polyethylene glycol chains. Various modifications, including of chain length or the number of chains, the presence of a metal atom in the porphyrin core, or having two or more porphyrin rings in the molecular architecture, result in a wide range of properties. These encompass self-assembly with different aggregate morphology, molecular recognition of biomolecules, and different photophysical responses, which can be translated into numerous promising applications in the sensing and biomedical field, based on turn-on/turn-off fluorescence and on photogeneration of radical species.

Nonlinear Optical Properties of Porphyrin, Fullerene and Ferrocene Hybrid Materials.

In this research, we investigated the second-order nonlinear optical (NLO) properties of multicomponent hybrid materials formed by meso-tetraphenylporphyrin P (both as free base and ZnII complex), carrying in 2 or 2,12 β-pyrrolic position an electron donor ferrocene (Fc), and/or an electron acceptor fullerene (C60) moiety, connected to the porphyrin core via an ethynyl or an ethynylphenyl spacer. We measured the NLO response by the electric-field-induced second-harmonic generation (EFISH) technique in CH2Cl2 solution with a 1907 nm incident wavelength, recording for all the investigated compounds unexpected negative values of μβ1907. Since density functional theory (DFT) calculations evidenced for P-Fc dyads almost null ground state dipole moments and very low values for P-C60 dyads and Fc-P-C60 triads, our EFISH results suggested a significant contribution to γEFISH of the purely electronic cubic term γ(−2ω; ω, ω, 0), which prevails on the quadratic dipolar orientational one μβ(−2ω; ω, ω)/5kT, as confirmed by computational evidence.

Impact of Changing the Core in Tetrapyrrolic Dendrimers Designed for Oxygen Sensitization: New Fluorescent Phthalocyanine-Based Dendrimers with High Two-Photon Absorption Cross-sections

In the continuation of our sustained interest for porphyrin-based dendrimers and their use as luminescent photo-sensitizers for two-photon photodynamic therapy (2P-PDT), we wondered about the effect of changing the central porphyrin core for a phthalocyanine core in these macromolecular structures. Thus, related phthalocyanine-based dendrimers possessing up to 16 conjugated 9,9-dibutyl-2-fluorenyl endgroups at their periphery were now prepared and studied. As for porphyrin analogues, it was found that an efficient energy transfer occurs from the peripheral fluorenyl units toward the central phthalocyanine unit of these compounds, leading to intense red light emission and photosensitization of oxygen. While the linear optical properties of these new dendrimers are only slightly improved compared to those of their porphyrin-cored analogues for PDT and fluorescence imaging, their two-photon absorption (2PA) cross-sections are much more significantly boosted, evidencing the key role played by the central tetrapyrrolic unit in this respect. The impact of this structural change in relation with the impact resulting from the change in dendrimer generations is then discussed with the help of DFT and molecular dynamic calculations.

Structural and spectral transformation of cationic porphyrin TMPyP4 at adsorption on graphene

Hybrids of graphene nanomaterials with porphyrins possess distinct photo and electronic properties that enable a wide spectrum of applications involving interaction with light. In this work we analyze structural and spectral transformations of cationic meso-5,10,15,20-tetra-(N-methyl-4-pyridyl) porphyrin (ТМРyР4) at adsorption on graphene. It is shown that the binding of TMPyP4 with graphene is stronger as compared to the neutral porphyrin (TPP) with a similar structure (-111.0 vs -22.6 kcal/mol). This is due to a large contribution from the cation-π-electrons interaction. The interaction of TMPyP4 with graphene is accompanied with a distortion of the flat structure of the porphyrin core and twisting of the side rings. As a result, the porphyrin molecule flattens. The cationic porphyrin adsorbed to graphene induces a stronger molecule flattening in comparison with the neutral porphyrin. A comparison of the experimental and calculated (DFT) UV spectra allows estimating the contribution of the π-π stacking and the twisting of the side rings to the observed red-shifting. The TMPyP4 molecule creates an area of negative potential in graphene close to the porphyrin adsorption site. The adsorption of TMPyP4 on graphene is also investigated with DFT calculations and with molecular dynamics simulations in water environment and in vacuum.

Photophysical study and in vitro approach against Leishmania panamensis of dicloro-5,10,15,20-tetrakis(4-bromophenyl)porphyrinato Sn(IV)

Background:Photodynamic therapy activity against different biological systems has been reported for porphyrins. Porphyrin modifications through peripheral groups and/or by metal insertion inside the ring are main alternatives for the improvement of its photo-physical properties. In this study, we synthesized and characterized 5,10,15,20-tetrakis(4-bromophenyl)porphyrin and the dicloro-5,10,15,20-tetrakis(4-bromophenyl)porphyrinato Sn(IV).Methods:Metal-free porphyrin was synthesized using the Alder method, while the Sn(IV)-porphyrin complex was prepared by combining metal-free porphyrin with stannous chloride in DMF; the reaction yields were 47% and 64% respectively. Metal-free porphyrin was characterized by UV-Vis, FT-IR, ESI-mass spectrometry and13C-NMR. Additionally, the Sn(IV) -porphyrin complex was characterized using UV-Vis and FT-IR. Cyclic voltammetry tests in four different solvents. The fluorescence quantum yield (Φf) was measured using fluorescein as a standard, the singlet oxygen quantum yield (ΦD) was estimated using the standard 5,10,15,20-(tetraphenyl)porphyrin (H2TPP) and the quencher of singlet oxygen 1,3-diphenylisobenzofuran (DPBF).Results:UV-Vis assay showed typical Q and Soret bands for porphyrin and its metallo-porphyrin complex. Compounds showed photoluminescence at the visible range of electromagnetic spectrum. The inclusion of the metal in the porphyrin core changed the Φffrom 0.15 to 0.05 and the ΦDincreased from 0.55 to 0.59. Finally, the effect of the compounds on the viability ofL. panamensiswas evaluated by means of the MTT test. The results showed that both compounds decreased the viability of the parasite; this inhibitory activity was greater under light irradiation; the porphyrin compound had IC50of 16.5 μM and the Sn(IV)-porphyrin complex had IC50of 19.2 μM.Conclusion:The compounds were synthesized efficiently, their characterization was carried out by different spectroscopy techniques and their own signals were evidenced for both structures, both compounds decreased the cell viability ofL. panamensis.

Porphyrin Acceptors with Two Perylene Diimide Dimers for Organic Solar Cells.

Three small-molecule acceptors (Por-PDI, TEHPor-PDI, and BBOPor-PDI) with different side chains were synthesized by using a porphyrin core as the electron-donating unit and connecting electron-withdrawing perylene diimide dimers via acetylene bridges. The bulk heterojunction organic solar cells based on the three acceptors and a polymer donor provided power conversion efficiencies (PCEs) of 3.68-5.21 % when the active layers were fabricated with pyridine additives. Though the synthesis of Por-PDI is easier with fewer reaction steps and higher yields, the devices based on Por-PDI showed the best performance with a PCE of 5.21 %. The more ordered intermolecular packing due to the reduced steric hindrance at the porphyrin core of Por-PDI could contribute to the more balanced hole/electron mobilities, higher maximum charge generation rate, and less bimolecular recombination in Por-PDI devices, which are beneficial for the higher PCE.

Wavelength-selective porphyrin photodiodes via control of Soret- and Q-band absorption

Porphyrin-based photodiode materials have mainly been targeted to achieve panchromatic absorption by maximizing the Soret- and Q-band absorption; however, they have rarely been studied with the purpose to make them wavelength-selective in photodetecting devices. In this study, we synthesized a wavelength-selective porphyrin material, PZn-FL, via Sonogashira coupling between an ethyne π-linked porphyrin core (PZn) and four fluorene (FL) moieties. The synthesized PZn-FL material showed a narrow full-width-at-half-maximum (FWHM) of 75 nm in the blue absorption region. The Q-band absorption of PZn-FL was significantly suppressed in organic photodiodes (OPDs), resulting in a blue-selective specific detectivity spectrum with a FWHM of 75 nm and a noise equivalent power of 2.86 × 10−12 W/Hz0.5. The planar backbone structure of PZn-FL was beneficial to increase charge transport and reduce bimolecular recombination, and the vertically oriented alkyl side chains of the PZn backbone contributed to prevent severe intermolecular aggregation and maintain a narrow absorption in film state.

Conformational Design of Enzyme-like Porphyrin Binding Pockets for Catalysis and Sensing

Porphyrins have long been recognized as sensors for various analytes. However, this involves mostly metalloporphyrins and there are still limitations with regard to discrimination and sensitivity. Here we illustrate that metal-free metal-free (‘free base’) porphyrins can be re-engineered via conformational design to make the core N-H units accessible for interaction with substrates or analytes. This allows to utilize metal-free porphyrin free bases as organocatalysts. Highly conjugated porphyrin macrocyclic systems offer spectrophotometric sensitivity towards geometrical and/or electronic changes and thus, utilizing the porphyrin core for selective detection of substrates in solution offers significant potential for applications. As a proof-of-concept we describe how a combination of macrocycle distortion in conjunction with suitable functional groups in the porphyrin periphery allowed the design of the binding pocket in an enzyme-like fashion and facilitated the highly selective detection of the pyrophosphate anion in a switchable sensor system.

(Invited) Beta, Beta-Functionalized Push-Pull Opp-Dibenzoporphyrins As Sensitizers for Dye-Sensitized Solar Cells: The Role of the Phenylethynyl Bridge and the Tertiary Amine Push Group

Significant progress has been made on dye-sensitized solar cells sensitized by push-pull porphyrins in recent years.1-3 An effective way to significantly enhance power conversion efficiencies of porphyrin dyes is through installation of push (electron-donating) and pull (electron-withdrawing) groups at porphyrin meso-positions.4-6 In this presentation, we present a different strategy to install push and pull groups at porphyrin beta-positions. Three series of novel opp-dibenzoporphyrins were prepared using this strategy. Our studies show significant push-pull effects for these porphyrins.7 DFT calculations suggest that the inclusion of ethynylphenyl bridge between the donating group and porphyrin core significantly segregate the frontier orbitals, which is a much-favored feature for sensitizers in DSSC. The electronic and optical properties of these beta-extended porphyrins were measured using UV-Vis spectroscopy, life-time and steady state fluorescence spectroscopy, cyclic voltammetry and transient spectroscopy. Their photovoltaic performances were tested in dye-sensitized solar cells. Reference T. Higashino and H. Imahori, Dalton Trans., 2015, 44, 448-463.M. Urbani, M. Gratzel, M. K. Nazeeruddin and T. Torres, Chem. Rev., 2014, 114, 12330-12396.L. L. Li and E. W. Diau, Chem. Soc. Rev., 2013, 42, 291-304.A. Yella, H.-W. Lee, H. N. Tsao, C. Yi, A. K. Chandiran, M. K. Nazeeruddin, E. W.-G. Diau, C.-Y. Yeh, S. M. Zakeeruddin and M. Grätzel, Science, 2011, 334, 629-634.S. Mathew, A. Yella, P. Gao, R. Humphry-Baker, B. F. Curchod, N. Ashari-Astani, I. Tavernelli, U. Rothlisberger, M. K. Nazeeruddin and M. Gratzel, Nat. Chem., 2014, 6, 242-247.G. Di Carlo, A. O. Biroli, F. Tessore, S. Caramori and M. Pizzotti, Coord. Chem. Rev., 2018, 358, 153-177.Y. Hu, S. Yellappa, M. B. Thomas, R. G. W. Jinadasa, A. Matus, M. Shulman, F. D'Souza and H. Wang, Chem Asian J, 2017, 12, 2749-2762.

Bis(1-methyl-imidazole)[meso-α,α,α,α-tetra-kis(o-nicotinamido-phen-yl)porphinato]iron(II)-1-methyl-imidazole-tetra-hydro-furan (1/1/1.5).

In the title compound, [FeII(C68H44N12O4)(C4H6N2)2]·C4H6N2·1.5C4H8O, the central FeII ion is coordinated by four pyrrole N atoms of the porphyrin core and two N atoms of the 1-methyl-imidazole ligands in the axial sites. One 1-methyl-imidazole and one and a half tetra-hydro-furan solvent mol-ecules are also present in the asymmetric unit. The complex exhibits a near planar porphyrin core conformation, in which the iron centre is slightly displaced towards the hindered porphyrin side (0.01 Å). The average Fe-Np (Np refers to the pyrrole nitro-gen atoms in the porphyrin) bond length is 1.990 (9) Å, and the axial Fe-NIm (NIm refers to the imidazole nitro-gen atoms) bond lengths are 1.993 (3) and 2.004 (3) Å. The dihedral angle between the two coordinated 1-methyl-imidazole planes is 56.6 (2)°. The dihedral angles between the 1-methyl-imidazole planes and the planes of the closest Fe-Np vector are 16.8 (2) and 39.8 (2)°. N-H⋯N and N-H⋯O inter-actions are observed in the crystal structure.