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Unlike their planar counterparts, classic synthetic protocols for C–C bond forming reactions on nonplanar porphyrins are underdeveloped. The development of C–C bond forming reactions on nonplanar porphyrins is critical in advancing this field of study for more complex porphyrin architectures, which could be used in supramolecular assemblies, catalysis, or sensing. In this work a library of arm-extended dodecasubstituted porphyrins was synthesized through the optimization of the classic Suzuki–Miyaura coupling of peripheral haloaryl substituents with a range of boronic acids. We report on palladium-catalyzed coupling attempts on the ortho-, meta-, and para-meso-phenyl position of sterically demanding dodecasubstituted saddle-shaped porphyrins. While para- and meta-substitutions could be achieved, ortho-functionalization in these systems remains elusive. Furthermore, borylation of a dodecasubstituted porphyrin’s meso-phenyl position was explored and a subsequent C–C coupling showed the polarity of the reaction can be reversed resulting in higher yields. X-ray analysis of the target compounds revealed the formation of supramolecular assemblies, capable of accommodating substrates in their void.

The crystal structure of (R,R)-4-bromo-2-{4-[4-bromo-1-(4-toluenesulfonyl)-1H-pyrrol-2-yl]-1,3-dinitrobutan-2-yl}-1-(4-toluenesulfonyl)-1H-pyrrole (1, C26H24Br2N4O8S2) is presented. The title compound was isolated in suitable yield as a by-product in our synthesis of geminal-dimethyl hydrodipyrrins. We observe an unforeseen enantiomeric resolution both in the bulk sample and the crystal of 1, with distinct C—H...O (Cmethyl—H...Onitro, Csp3—H...Osulfonyl) interactions observed in the enantiomers present, along with other interactions, namely C5-pyrrolyl—H...Osulfonyl, forming a polymer along the crystallographic c-axis direction. Whilst pyrrolic fragments are well documented in the literature, little data is found surrounding the 1,3-dinitrobutane scaffold.

The crystal structures of three S-(pyridin-2-yl) benzothioesters with varying para-phenyl substituents are presented, namely, S-(pyridin-2-yl) 4-nitrobenzothioate (1, C12H8N2O3S), S-(pyridin-2-yl) 4-methylbenzothioate (2, C13H11NO2S) and S-(pyridin-2-yl) 4-methoxybenzothioate (3, C13H11NO2S). This class of compounds are used in the mono-acylation of pyrrolic species to yield multifunctional tetrapyrroles. The structures presented herein are the first of their compound class. The dominant interactions present in this series are π–π stacking and C—H...O interactions, and as the para-phenyl motif changes from electron withdrawing (NO2, 1) to electron donating (OCH3, 3), changes are observed in the interactions present in the crystal packing, from predominant π–π stacking in 1 to exclusively C—H...O/N interactions (Caryl—H...Ocarbonyl, C—H...Omethoxy and Caryl—H...Npyridine) in 3.

Abstract Two graphene oxide nanoassemblies using 5-(4-(aminophenyl)-10,15,20-triphenylporphyrin (TPPNH2) were fabricated by two synthetic methods: covalent (GO-CONHTPP) and noncovalent bonding. GO-CONHTPP was achieved through amide formation at the periphery of GO sheets and the hybrid material was fully characterized by FTIR, XPS, Raman spectroscopy, and SEM. Spectroscopic measurements together with theoretical calculations demonstrated that assembling TPPNH2 on the GO surface in DMF-H2O (1:2, v/v) via non-covalent interactions causes changes in the absorption spectra of porphyrin, as well as efficient quenching of its emission. Interestingly, covalent binding to GO does not affect notably neither the porphyrin absorption nor its fluorescence. Theoretical calculations indicates that close proximity and π–π-stacking of the porphyrin molecule with the GO sheet is possible only for the non-covalent functionalization. Femtosecond pump–probe experiments revealed that only the non-covalent assembly of TPPNH2 and GO enhances the efficiency of the photoinduced electron transfer from porphyrin to GO. In contrast to the non-covalent hybrid, the covalent GO-CONHTPP material can generate singlet oxygen with quantum yields efficiency (ΦΔ = 0.20) comparable to that of free TPPNH2 (ΦΔ = 0.26), indicating the possible use of covalent hybrid materials in photodynamic/photothermal therapy. The spectroscopic studies combined with detailed quantum-chemical analysis provide invaluable information that can guide the fabrication of hybrid materials with desired properties for specific applications.

The use of halogens in the crystal engineering of supramolecular porphyrin assemblies has been a topic of strong interest over the past decades. With this in mind we have characterized a series of direct meso-halogenated porphyrins using single crystal X-ray crystallography. This is accompanied by a detailed conformational analysis of all deposited meso-halogenated porphyrins in the CSD. In this study we have used the Hirshfeld fingerprint plots together with normal-coordinate structural decomposition and determined crystal structures to elucidate the conformation, present intermolecular interactions, and compare respective contacts within the crystalline architectures. Additionally, we have used density functional theory calculations to determine the structure of several halogenated porphyrins. This contrasts conformational analysis with existing X-ray structures and gives a method to characterize samples that are difficult to crystallize. By using the methods outlined above we were able to deduce the impact a meso halogen has on a porphyrin, for example, meso-halogenation is dependent on the type of alternate substituents present when forming supramolecular assemblies. Furthermore, we have designed a method to predict the conformation of halogenated porphyrins, without need of crystallization, using DFT calculations with a high degree of accuracy.

The crystal structures of three intermediate compounds in the synthesis of 8-bromo-2,3,4,5-tetrahydro-1,3,3-trimethyldipyrrin are reported; 4-bromo-2-formyl-1-tosyl-1H-pyrrole, C12H10BrNO3S, (E)-4-bromo-2-(2-nitrovinyl)-1-tosyl-1H-pyrrole, C13H11BrN2O4S, and 6-(4-bromo-1-tosylpyrrol-2-yl)-4,4-dimethyl-5-nitrohexan-2-one, C19H23BrN2O5S. The compounds show multitudinous intermolecular C—H...O interactions, with bond distances and angle consistent in the series and within expectations, as well as varied packing types. The merits of collecting data beyond the standard resolution usually reported for small molecules are discussed.

Herein, 9,10-diethynyltriptycene is investigated for its use as a rigid isolating unit in the synthesis of multichromophoric arrays. Sonogashira cross-coupling conditions are utilized to attach various porphyrins and boron dipyrromethenes (BODIPYs) to the triptycene scaffold. While there are previous examples of triptycene porphyrin complexes, this work reports the first example of a linearly connected porphyrin dimer, linked through the bridgehead carbons of triptycene. Symmetric and unsymmetric examples of these complexes are demonstrated and single crystal X-ray analysis of an unsymmetrically substituted porphyrin dimer highlights the evident linearity in these systems. Moreover, initial UV–vis and fluorescence studies show the promise of triptycene as a linker for electron transfer studies, showcasing its isolating nature.

The crystal structures of the title compounds, two solvates (CHCl3 and THF) of a symmetric and highly substituted porphyrin, C44H2Br8F20N4 or OBrTPFPP, are described. These structures each feature a non-planar porphyrin ring, exhibiting a similar conformation of the strained ring independent of solvent identity. These distorted porphyrins are able to form hydrogen bonds and sub-van der Waals halogen interactions with enclathrated solvent; supramolecular interactions of proximal macrocycles are additionally affected by solvent choice. The crystal studied for compound 1·CHCl3 was refined as an inversion twin. One pentafluorophenyl group was modelled as disordered over two sites [occupancy ratio = 0.462 (7):0.538 (7)]. The chloroform solvate was also modelled as disordered over two orientations [occupancy ratio = 0.882 (7): 0.118 (7).

Within this work, we review the metal coordination effect on the photophysics of metal dipyrrinato complexes. Dipyrrinato complexes are promising candidates in the search for alternative transition metal photosensitizers for application in photodynamic therapy (PDT). These complexes can be activated by irradiation with light of a specific wavelength, after which, cytotoxic reactive oxygen species (ROS) are generated. The metal coordination allows for the use of the heavy atom effect, which can enhance the triplet generation necessary for generation of ROS. Additionally, the flexibility of these complexes for metal ions, substitutions and ligands allows the possibility to tune their photophysical properties. A general overview of the mechanism of photodynamic therapy and the properties of the triplet photosensitizers is given, followed by further details of dipyrrinato complexes described in the literature that show relevance as photosensitizers for PDT. In particular, the photophysical properties of Re(I), Ru(II), Rh(III), Ir(III), Zn(II), Pd(II), Pt(II), Ni(II), Cu(II), Ga(III), In(III) and Al(III) dipyrrinato complexes are discussed. The potential for future development in the field of (dipyrrinato)metal complexes is addressed, and several new research topics are suggested throughout this work. We propose that significant advances could be made for heteroleptic bis(dipyrrinato)zinc(II) and homoleptic bis(dipyrrinato)palladium(II) complexes and their application as photosensitizers for PDT.

Coordinating the spatial arrangement of electroactive partners is crucial to designable molecular electronics and photonics. Porphyrins are ubiquitous reaction centers in nature; synthetic porphyrins, in the crystallographic solid state, are often coerced into monolithic stacks, inhibiting reactivity. Using the principles of self-organization, and by exploiting charge-balance principles, we can manipulate nonplanar porphyrins into one- and two-dimensional hydrogen-bonded polymers, with polyoxometalate (POM) and bifunctional counter-anions serving as linkers. Herein, we report 11 crystal structures as a systematic study of the interactions between dodecasubstituted porphyrin acids and nonstandard counterions, as well as the induced conformations in the porphyrin core. We can show that this hydrogen bond chelate is a viable method of organizing electroactive centers into filaments and monolayers for surface deposition and ultrathin devices.

The title compound, C11H9NOS, was obtained in an improved yield compared to previous literature methods. The molecule is essentially planar with a maximum deviation of 0.085 Å from the mean plane through all non-H atoms. There is directive intermolecular hydrogen bonding in the form of N—H...O hydrogen bonds with a distance of 2.889 (3) Å between the pyrrole amine and the ketone carbonyl O atom. The resulting hydrogen-bonding network defines a ribbon parallel to the a axis. These ribbons form offset stacks along the b axis.

Environmental pollution with chiral organic compounds is an emerging problem requiring innovative sensing methods. Amino-functionalized thioureas, such as 2-(dimethylamino)cyclohexyl-(3,5-bis(trifluoromethyl)phenyl)thiourea (Takemoto’s catalyst), are widely used organocatalysts with virtually unknown environmental safety data. Ecotoxicity studies based on the Vibrio fischeri luminescence inhibition test reveal significant toxicity of Takemoto’s catalyst (EC50 = 7.9 mg/L) and its NH2-substituted analog (EC50 = 7.2–7.4 mg/L). The observed toxic effect was pronounced by the influence of the trifluoromethyl moiety. En route to the porphyrin-based chemosensing of Takemoto-type thioureas, their supramolecular binding to a series of zinc porphyrins was studied with UV-Vis and circular dichroism (CD) spectroscopy, computational analysis and single crystal X-ray diffraction. The association constant values generally increased with the increasing electron-withdrawing properties of the porphyrins and electron-donating ability of the thioureas, a result of the predominant Zn⋯N cation–dipole (Lewis acid–base) interaction. The binding event induced a CD signal in the Soret band region of the porphyrin hosts—a crucial property for chirality sensing of Takemoto-type thioureas.

The development of new antimicrobial strategies that act more efficiently than traditional antibiotics is becoming a necessity to combat multidrug-resistant pathogens. Here we report the efficacy of laser-light-irradiated 5,10,15,20-tetrakis(m-hydroxyphenyl)porphyrin (mTHPP) loaded onto an ethylcellulose (EC)/chitosan (Chs) nanocomposite in eradicating multi-drug resistant Pseudomonas aeruginosa, Staphylococcus aureus, and Candida albicans. Surface loading of the ethylcelllose/chitosan composite with mTHPP was carried out and the resulting nanocomposite was fully characterized. The results indicate that the prepared nanocomposite incorporates mTHPP inside, and that the composite acquired an overall positive charge. The incorporation of mTHPP into the nanocomposite enhanced the photo- and thermal stability. Different laser wavelengths (458; 476; 488; 515; 635 nm), powers (5–70 mW), and exposure times (15–45 min) were investigated in the antimicrobial photodynamic therapy (aPDT) experiments, with the best inhibition observed using 635 nm with the mTHPP EC/Chs nanocomposite for C. albicans (59 ± 0.21%), P. aeruginosa (71.7 ± 1.72%), and S. aureus (74.2 ± 1.26%) with illumination of only 15 min. Utilization of higher doses (70 mW) for longer periods achieved more eradication of microbial growth.

Metal-organic frameworks (MOFs) encompass a rapidly expanding class of materials with diverse potential applications including gas storage, molecular separation, sensing and catalysis. So-called ‘rod MOFs’, which comprise infinitely extended 1D secondary building units (SBUs), represent an underexplored subclass of MOF. Further, porphyrins are considered privileged ligands for MOF synthesis due to their tunable redox and photophysical properties. In this study, the CuII complex of 5,15-bis(4-carboxyphenyl)-10,20-diphenylporphyrin (H2L-CuII, where H2 refers to the ligand’s carboxyl H atoms) is used to prepare two new 2D porphyrinic rod MOFs PROD-1 and PROD-2. Single-crystal X-ray analysis reveals that these frameworks feature 1D MnII- or CoII-based rod-like SBUs that are coordinated by labile solvent molecules and photoactive porphyrin moieties. Both materials were characterised using infrared (IR) spectroscopy, powder X-ray diffraction (PXRD) spectroscopy and thermogravimetric analysis (TGA). The structural attributes of PROD-1 and PROD-2 render them promising materials for future photocatalytic investigations.

In the title free base porphyrin, C42H34N4, the neighbouring N...N distances in the center of the ring vary from 2.818 (8) to 2.998 (8) Å and the phenyl rings are tilted from the 24-atom mean plane at angles varying between 62.42 (2)–71.63 (2)°. The NH groups are involved in intramolecular bifurcated N—H...(N,N) hydrogen bonds. The Ca—Cm—Ca angles vary slightly for the phenyl rings, between 124.19 (18)–126.17 (18)°. The largest deviation from the mean plane of the 24-atom macrocycle is associated with the meso carbon at the substituted tert-butyl position, which is displaced from the mean plane by 0.44 (2) Å. The free base porphyrin is characterized by a significant degree of ruffled (B1u) distortion with contributions from domed (A2u) and wave [Eg(y) and Eg(x)] modes. In the crystal, molecules are linked by a number of weak C—H...π interactions, forming a three-dimensional framework. The structure was refined as a two-component inversion twin.

Photodynamic therapy (PDT) is a promising cancer treatment which involves a photosensitizer (PS), light at a specific wavelength for PS activation and oxygen, which combine to elicit cell death. While the illumination required to activate a PS imparts a certain amount of selectivity to PDT treatments, poor tumor accumulation and cell internalization are still inherent properties of most intravenously administered PSs. As a result, common consequences of PDT include skin photosensitivity. To overcome the mentioned issues, PSs may be tailored to specifically target overexpressed biomarkers of tumors. This active targeting can be achieved by direct conjugation of the PS to a ligand with enhanced affinity for a target overexpressed on cancer cells and/or other cells of the tumor microenvironment. Alternatively, PSs may be incorporated into ligand-targeted nanocarriers, which may also encompass multi-functionalities, including diagnosis and therapy. In this review, we highlight the major advances in active targeting of PSs, either by means of ligand-derived bioconjugates or by exploiting ligand-targeting nanocarriers.

Individual chemical motifs are known to introduce structural distortions to the porphyrin macrocycle, be it in the core or at the periphery of the macrocycle. The interplay when introducing two or more of these known structural motifs has been scarcely explored and is not necessarily simply additive; these structural distortions have a chance to compound or negate to introduce new structural types. To this end, a series of compounds with complementary peripheral (5,15-disubstitution) and core (acidification) substitution patterns were investigated. The single-crystal X-ray structures of 18 5,15-diphenylporphyrin, 5,15-diphenylporphyrindi-ium diacid, and related compounds are reported, including the first example of a 5,15-dialkylporphyrindi-ium. Normal-coordinate structural decomposition (NSD) analysis is used for a detailed analysis of the conformation of the porphyrin subunit within the crystal structures. An elongation of porphyrin macrocycles along the C5,C15- axis (B2g symmetry) is observed in all of the free base porphyrins and porphyrin dications; distance across the core is around 0.3 Å in the free base and diacid compounds, and more than doubled in 5,15-dipentylporphyrin and 5,15-dipentylporphyrindi-ium diacid. While the free base porphyrins are largely planar, a large out-of-plane distortion can be observed in 5,15-diphenylporphyrin diacids, with the expected “projective saddle” shape characteristic for such systems. The combination of these two distortions (B2u and B2g) from regular porphyrin structure results in a macrocycle best characterized in the chiral point-group D2. A rare structural type of a cis-hydrogen bond chelate is observed for 5,15-dipentylporphyrindi-ium diacid, which adopts an achiral C2v symmetry. Crystallographic data indicate that the protonated porphyrin core forms hydrogen bonding chelates (N-H⋯X⋯H-N) to counter-anions. Weaker interactions, such as induced intramolecular C-H⋯O interactions from the porphyrin periphery are described, with distances characteristic of charge-assisted interactions. This paper offers a conceptual framework for accessing porphyrin macrocycles with designable distortion and symmetry, useful for the selective perturbation of electronic states and a design-for-application approach to solid state porphyrin materials.

In this study, a novel series of 1,2-disubstituted benzo[d]imidazoles was rationally designed as VEGFR-2 inhibitors targeting hepatocellular carcinoma. Our design strategy is two-fold; it aimed first at studying the effect of replacing the 5-methylfuryl moiety of the well-known antiangiogenic 2-furylbenzimidazoles with an isopropyl moiety on the VEGFR-2 inhibitory activity and the cytotoxic activity. Our second objective was to further optimize the structures of the benzimidazole derivatives through elongation of the side chains at their one-position for the design of more potent type II-like VEGFR-2 inhibitors. The designed 1,2-disubstituted benzimidazoles demonstrated potent cytotoxic activity against the HepG2 cell line, reaching IC50 = 1.98 μM in comparison to sorafenib (IC50 = 10.99 μM). In addition, the synthesized compounds revealed promising VEGFR-2 inhibitory activity in the HepG2 cell line, e.g., compounds 17a and 6 showed 82% and 80% inhibition, respectively, in comparison to sorafenib (% inhibition = 92%). Studying the effect of 17a on the HepG2 cell cycle demonstrated that 17a arrested the cell cycle at the G2/M phase and induced a dose-dependent apoptotic effect. Molecular docking studies of the synthesized 1,2-disubstituted benzimidazoles in the VEGFR-2 active site displayed their ability to accomplish the essential hydrogen bonding and hydrophobic interactions for optimum inhibitory activity.

The asymmetric unit of the title nickel(II) porphyrin, [Ni(C48H60N4O2)], contains one independent molecule. The average Ni—N bond length is 1.917 (13) Å. The molecules are arranged in a closely spaced lattice structure in which neighbouring porphyrins are oriented in inversion-related dimers. The nickel(II) porphyrin is characterized by a significant degree of a ruffled (B1u) conformation with small contributions from saddle (B2u) and wave (y) [Eg(y)], as determined using normal structural decomposition. Disorder in the 2,5-dimethoxyphenyl substituent was modelled over two positions with a 60% occupancy for the major moiety. One of the ethyl groups is also disordered over two positions and was modelled with the major moiety being present in 51.3% occupancy.

In the title compound, C8H9BO4, the methoxycarbonyl group is rotated out of the plane of the benzene ring by 7.70 (6)°. In the crystal, molecules are linked via pairs of O—H...O hydrogen bonds, involving the boronic acid OH groups, forming inversion dimers. The dimers are linked via O—H...O hydrogen bonds, involving a boronic acid OH group and the carbonyl O atom, forming undulating sheets parallel to (10-2). Within the sheets there are also C—H...O hydrogen bonds present, also involving the carbonyl O atom. The sheets are linked via C—H...π and offset face-to-face π-interactions between inversion-related molecules [inter-centroid distance = 3.7843 (16) Å, interplanar distance = 3.3427 (4) Å and offset = 1.744 Å], forming a three-dimensional structure.

Chlorophylls are a fundamental class of tetrapyrroles and function as the central reaction center, accessory and photoprotective pigments in photosynthesis. Their unique individual photochemical properties are a consequence of the tetrapyrrole macrocycle, the structural chemistry and coordination behavior of the phytochlorin system, and specific substituent pattern. They achieve their full potential in solar energy conversion by working in concert in highly complex, supramolecular structures such as the reaction centers and light-harvesting complexes of photobiology. The biochemical function of these structures depends on the controlled interplay of structural and functional principles of the apoprotein and pigment cofactors. Chlorophylls and bacteriochlorophylls are optically active molecules with several chiral centers, which are necessary for their natural biological function and the assembly of their supramolecular complexes. However, in many cases the exact role of chromophore stereochemistry in the biological context is unknown. This review gives an overview of chlorophyll research in terms of basic function, biosynthesis and their functional and structural role in photosynthesis. It highlights aspects of chirality and symmetry of chlorophylls to elicit further interest in their role in nature.

In the title compound, C44H37BN4O2, the dihedral angle between the plane of the porphyrin macrocycle ring system [r.m.s. deviation = 0.159 (1) Å] and those of three phenyl rings are 66.11 (4), 74.75 (4) and 57.00 (4)°. The conformational distortion is characterized by a mixture of ruffled, saddle and in-plane distortion modes. In the crystal, the porphyrin molecules are linked by C—H...π interactions into supramolecular chains running along the a-axis direction. A pair of bifurcated N—H...(N,N) hydrogen bonds occur across the central region of the macrocycle.

The asymmetric unit of the title compound, [Ni(C32H36N4)], contains two independent molecules exhibiting an overall ruffled conformation of the porphyrin macrocycle and differing mainly in the positions of the methyl groups. The average Ni—N bond lengths are 1.912 (2) and 1.910 (2) Å in the two molecules. The molecules form a closely spaced lattice structure in which neighbouring porphyrins are oriented in a nearly perpendicular fashion to each other. The compound was prepared via nucleophilic substitution of (5,15-diisobutylporphyrinato)nickel(II) with n-butyllithium.

In the title compound, C42H42N4O2, the complete molecule is generated by a crystallographic inversion centre. The porphyrin system exhibits a near planar macrocycle conformation with an average deviation from the least-squares plane of the 24 macrocycle atoms of 0.037 (5) Å. The phenyl ipso C atoms are positioned above and below the porphyrin plane by 0.35 (1) Å and the macrocycle shows evidence of in-plane rectangular elongation with N...N separations of 3.032 (5) and 2.803 (5) Å. Two intramolecular N—H...N hydrogen bonds occur.

The title compound, [Ni(C28H28N4)], crystallizes with two independent molecules in the unit cell, one of which is located on an inversion center. Both macrocycles exhibit a planar conformation with average deviation from the least-squares-plane of the 24 macrocycle atoms of Δ24 = 0.043 Å for the first molecule and 0.026 Å for the molecule located on an inversion center. The average Ni—N bond lengths are 1.955 (2) and 1.956 (2) Å in the two molecules. The molecules form π–π dimers of intermediary strength with a mean plane separation of 3.36 (2) Å.

The title compound, [Pt(C42H48N4)], was obtained through metallation of the corresponding free base with PtCl2, followed by crystallization from methylene chloride/methanol. The molecule exhibits an almost planar macrocycle with an average deviation of the 24 macrocyclic atoms from their least-squares plane (Δ24) of 0.04 Å and an average Pt—N bond length of 2.022 Å. Despite the unsymmetrical substitution pattern, there is no significant difference between distortion of the geometry at the phenyl substituted meso position and those of unsubstituted meso positions.

The title compound, [Ni(C40H28N4O)], was obtained from a Grignard reaction of the respective formylporphyrin to yield {5-[hydroxy(phenyl)methyl]-10,20-diphenylporphyrinato}nickel(II), followed by crystallization from methylene chloride/methanol. The molecule exhibits a ruffled macrocycle with an average deviation of the 24 macrocycle atoms from their least-squares plane (Δ24) of 0.26 Å and an average Ni—N bond length of 1.931 (2) Å. In line with the asymmetrical substituent pattern, the degree of distortion is slightly larger at point of attachment of the methoxy(phenyl)methyl residue than at the unsubstituted meso position. The methoxy group attached to the chiral C atom is disordered in a 0.534 (4):0.466 (4) ratio.

The importance of molecular conformation to the nature and strength of noncovalent interactions existing between a series of increasingly nonplanar tetraphenylporphyrin (TPP) derivatives and carbon nanotubes was systematically investigated experimentally in solution using a range of linear and nonlinear optical techniques. Additional complementary molecular dynamics studies were found to support the experimental observations. Convincing evidence of binding between single walled nanotubes (SWNTs) and some of these porphyrins was discovered, and a nonplanar macrocycle conformation was found to increase the likelihood of noncovalent binding onto nanotubes. Nonlinear optical studies showed that the optical limiting behavior of the TPP derivatives deteriorated with increasing porphyrin nonplanarity, but that formation of nanotube composites dramatically improved the optical limiting properties of all molecules studied. It was also found that the significant photoluminescence quenching behavior reported in the literature for such porphyrin/SWNT composites is at least partly caused by photoluminescence and excitation self-absorption and is, therefore, an artifact of the system.

The title compound, [Ni(C60H52N4)], is an example of a meso tetrasubstituted nickel(II) porphyrin with both meso aryl and alkyl residues. The molecule exhibits a planar macrocycle with an average deviation of the 24 macrocycle atoms from their least-squares plane (Δ24) of 0.01 Å and an average Ni—N bond length of 1.960 (2) Å. The NiII atom lies on a center of inversion. The structure presents a rare example for a planar nickel(II) porphyrin, as meso-substituted nickel(II) porphyrins with either only meso-aryl or with meso-alkyl residues typically exhibit a ruffled conformation.