Synthesis and structure of 16 pi octaalkyltetraphenylporphyrins

Nonplanar porphyrins: synthesis, properties, and unique functionalities

Porphyrins are variously substituted tetrapyrrolic macrocycles, with wide-ranging biological and chemical applications derived from metal chelation in the core and the 18π aromatic surface. Under suitable conditions, the porphyrin framework can deform significantly from regular planar shape, owing to steric overload on the porphyrin periphery or steric repulsion in the core, among other structure modulation strategies. Adopting this nonplanar porphyrin architecture allows guest molecules to interact directly with an exposed core, with guest-responsive and photoactive electronic states of the porphyrin allowing energy, information, atom and electron transfer within and between these species. This functionality can be incorporated and tuned by decoration of functional groups and electronic modifications, with individual deformation profiles adapted to specific key sensing and catalysis applications. Nonplanar porphyrins are assisting breakthroughs in molecular recognition, organo- and photoredox catalysis; simultaneously bio-inspired and distinctly synthetic, these molecules offer a new dimension in shape-responsive host-guest chemistry. In this review, we have summarized the synthetic methods and design aspects of nonplanar porphyrin formation, key properties, structure and functionality of the nonplanar aromatic framework, and the scope and utility of this emerging class towards outstanding scientific, industrial and environmental issues.

Core-modified porphyrins: novel building blocks in chemistry

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.

Changes in porphyrin’s conjugation based on synthetic and post-synthetic modifications

Porphyrins or more broadly defined porphyrinoids are the structures where the extended π-cloud can be significantly modified by several factors. The broad range of introduced structural motifs has shown a possibility of modification of conjugation by a controlled synthetic approach, leading to expected optical or magnetic behaviour, and also by post-synthetic modifications (i.e. redox or protonation/deprotonation), Both approaches lead to noticeab changes in observed properties but also open a potential for further utilization. Thus, this already constituted big family of macrocyclic structures with specific highly extended π-delocalization shows a significant contribution in several fields from fundamental studies, leading to understanding behaviour of skeletons like that with a substantial influence on biological studies and material science. The presented material focuses on the most significant examples of modifications of porphyrinoids skeleton leading to drastic changes in optical response and magnetic properties. Through the presentation, the focus will be placed on the changes leading to the most red-shifted transition as the parameter indicating extending the π-delocalization. Significantly different magnetic character will be also discussed based on the switching between aromatic/antiaromatic character assigned to macrocyclic structures that will be included.

A cationic benzocorrole Cu(ii) complex as a highly stable antiaromatic system

A highly stable 16π-electron antiaromatic system based on a monocationic tetrabenzocorrole Cu(ii) complex is reported.

A coupled polymeric porphyrin complex as a novel cathode for highly stable lithium organic batteries

A highly conjugated polymeric porphyrin with an ethynyl group is proposed as a new cathode for lithium organic batteries. The electrochemical performance is significantly improved after a simple coupled polymerization, resulting in excellent cycling stability with a capacity retention of 99.2% for 2000 cycles.

A Comprehensive Study on Tetraaryltetrabenzoporphyrins

Tetraaryltetrabenzoporphyrins (TATBPs) show, due to their optoelectronic properties, rising potential as dyes in various fields of physical and biomedical sciences. However, unlike in the case of porphyrins, the potential structural diversity of TATBPs has been explored only to little extent, owed mainly to synthetic hurdles. Herein, we prepared a comprehensive library of 30 TATBPs and investigated their fundamental properties. We elucidated structural properties by X-ray crystallography and found explanations for physical properties such as solubility. Fundamental electronic aspects were studied by optical spectroscopy as well as by electrochemistry and brought in context to the stability of the molecules. Finally, we were able to develop a universal synthetic protocol, utilizing a readily established isoindole synthon, which gives TATBPs in high yields, regardless of the nature of the used arylaldehyde and without meticulous chromatographic purifications steps. This work serves as point of orientation for scientists, that aim to utilize these molecules in materials, nanotechnological, and biomedical applications.

Redox-Associated Variation of Hückel Aromaticity from Lactam-Embedded Smallest Antiaromatic trans-Doubly N-Confused Porphyrins: Synthesis and Characterization

High-yield synthesis, spectroscopic and solid-state structural proof of the lactam-embedded smallest ever metal-free stable Hückel antiaromatic trans-doubly N-confused [16] porphyrins are reported. These new facets of trans-doubly N-confused porphyrins have been anticipated to exhibit the redox-associated variation of Hückel aromaticity as a mere consequence of the amido-like structures of the N-confused N-methyl pyrrole rings of the macrocycles. Strong aromaticity upon NaBH₄ reduction leading to a resonance dipolar structure of the [18]π-conjugated system as the reduced congener with concomitant Hückel topology are the important highlights. Excellent agreement between experimental spectroscopic measurements and the theoretically determined properties elucidate aromaticity switching upon chemical reduction. Recent years have witnessed an upsurge of demand for the experimental realization of stable antiaromatic systems because of their versatile applications in material science. The conformational rigidity and the enriched stability of these novel 16π antiaromatic doubly N-confused porphyrins might entitle these macrocycles toward such applications.

Molecular Engineering of Free-Base Porphyrins as Ligands-The N-H⋅⋅⋅X Binding Motif in Tetrapyrroles

The core N-H units of planar porphyrins are often inaccessible to forming hydrogen-bonding complexes with acceptor molecules. This is due to the fact that the amine moieties are "shielded" by the macrocyclic system, impeding the formation of intermolecular H-bonds. However, methods exist to modulate the tetrapyrrole conformations and to reshape the vector of N-H orientation outwards, thus increasing their availability and reactivity. Strategies include the use of porpho(di)methenes and phlorins (calixphyrins), as well as saddle-distorted porphyrins. The former form cavities due to interruption of the aromatic system. The latter are highly basic systems and capable of binding anions and neutral molecules via N-H⋅⋅⋅X-type H-bonds. This Review discusses the role of porphyrin(oid) ligands in various coordination-type complexes, means to access the core for hydrogen bonding, the concept of conformational control, and emerging applications, such as organocatalysis and sensors.

Diaqua-β-octaferrocenyltetraphenylporphyrin: a multiredox-active and air-stable 16π non-aromatic species

Herein the synthesis and properties of the first β-octaferrocenyltetraphenylporphyrin, {TPPFc₈(H₂O)₂}, in its extraordinary stable and non-aromatic 16π form are reported, showing seven separate reversible redox events.

Structure and conformation of photosynthetic pigments and related compounds. 15. Conformational analysis of chlorophyll derivatives – implications for hydroporphyrinsin vivo

Controlling the function of chlorophylls depends in part on their 3D conformation. The NSD program presents a powerful tool to identify the distortion modes in phytochlorins.

Redox switchable 19π and 18π 5,10,20-triaryl-5,15-diazaporphyrinoid–nickel(II) complexes

The synthesis and optical, electrochemical, and magnetic properties of nickel(II) complexes of 5,10,20-triaryl-5,15-diazaporphyrin (TriADAP) are reported. Metal-templated cyclization of unsymmetrically substituted nickel(II)–bis(1-amino-9-chloro-5-mesityldipyrrin; mesityl = 2,4,6-trimethylphenyl) complexes afforded the corresponding TriADAPs or 5-aryl-15-benzyl-10,20-dimesityl-5,15-diazaporphyrin, depending on the combination of base and solvent. The latter macrocycle was converted to TriADAP by deprotection of the [Formula: see text]-benzyl group through Pd/C-promoted hydrogenation. TriADAPs were isolated in both 18[Formula: see text] (cation) and 19[Formula: see text] (neutral) forms. The interconversion between these two oxidation states resulted in a distinct change in the optical properties of the DAP [Formula: see text]-system. NMR spectroscopy of the 18[Formula: see text] TriADAP cations showed that they had aromatic character, whereas EPR spectroscopy of the 19[Formula: see text] TriADAP showed a highly delocalized electron spin of the [Formula: see text]-radical. The para substituents of the [Formula: see text]-aryl groups of TriADAPs had a small but distinct impact on their HOMO and LUMO energies. The change in the net charge of one electron was directly reflected in the redox properties of the DAP ring; TriADAP was more easily reduced and less easily oxidized than DAP. The difference in the net charge was also reflected by the shielding of the pyrrolic [Formula: see text]-protons observed in the [Formula: see text]H NMR spectra. The present results confirm that TriADAP is a highly promising framework for constructing a new class of azaporphyrin-based materials with 18[Formula: see text]–19[Formula: see text] redox-switchable optical and magnetic properties.

Aromaticity as a Guiding Concept for Spectroscopic Features and Nonlinear Optical Properties of Porphyrinoids

With their versatile molecular topology and aromaticity, porphyrinoid systems combine remarkable chemistry with interesting photophysical properties and nonlinear optical properties. Hence, the field of application of porphyrinoids is very broad ranging from near-infrared dyes to opto-electronic materials. From previous experimental studies, aromaticity emerges as an important concept in determining the photophysical properties and two-photon absorption cross sections of porphyrinoids. Despite a considerable number of studies on porphyrinoids, few investigate the relationship between aromaticity, UV/vis absorption spectra and nonlinear properties. To assess such structure-property relationships, we performed a computational study focusing on a series of Hückel porphyrinoids to: (i) assess their (anti)aromatic character; (ii) determine the fingerprints of aromaticity on the UV/vis spectra; (iii) evaluate the role of aromaticity on the NLO properties. Using an extensive set of aromaticity descriptors based on energetic, magnetic, structural, reactivity and electronic criteria, the aromaticity of [4n+2] π-electron porphyrinoids was evidenced as was the antiaromaticity for [4n] π-electron systems. In agreement with previous studies, the absorption spectra of aromatic systems display more intense B and Q bands in comparison to their antiaromatic homologues. The nature of these absorption bands was analyzed in detail in terms of polarization, intensity, splitting and composition. Finally, quantities such as the average polarizability and its anisotropy were found to be larger in aromatic systems, whereas first and second hyperpolarizability are influenced by the interplay between aromaticity, planarity and molecular symmetry. To conclude, aromaticity dictates the photophysical properties in porphyrinoids, whereas it is not the only factor determining the magnitude of NLO properties.

A 1,5-Naphthyridine-Fused Porphyrin Dimer: Intense NIR Absorption and Facile Redox Interconversion with Its Reduced Congener

Pt^II -catalyzed cyclization of β-to-β ethynylene-bridged meso-amino Ni^II porphyrin dimer 4 followed by oxidation with PbO₂ afforded 1,5-naphthyridine-fused porphyrin dimer 5 in good yield. This dimer possesses a redox-active 1,4-diazabutadiene linkage that is interconvertible with its reduced 1,2-diaminoethene linkage upon treatments with NaBH₄ or PbO₂ . The dimer 5 exhibits an intense NIR absorption and a narrow HOMO-LUMO gap with a remarkably low reduction potential mainly due to effective bonding interactions in the LUMO through the 1,4-diazabutadiene linkage. In contrast, the reduced dimer 7 is fairly electron-rich with high HOMO energy and shows a relatively large HOMO-LUMO gap compared to that of 5.

A Porphyrin Complex as a Self-Conditioned Electrode Material for High-Performance Energy Storage

The novel functionalized porphyrin [5,15-bis(ethynyl)-10,20-diphenylporphinato]copper(II) (CuDEPP) was used as electrodes for rechargeable energy-storage systems with an extraordinary combination of storage capacity, rate capability, and cycling stability. The ability of CuDEPP to serve as an electron donor or acceptor supports various energy-storage applications. Combined with a lithium negative electrode, the CuDEPP electrode exhibited a long cycle life of several thousand cycles and fast charge-discharge rates up to 53 C and a specific energy density of 345 Wh kg^-1 at a specific power density of 29 kW kg^-1 . Coupled with a graphite cathode, the CuDEPP anode delivered a specific power density of 14 kW kg^-1 . Whereas the capacity is in the range of that of ordinary lithium-ion batteries, the CuDEPP electrode has a power density in the range of that of supercapacitors, thus opening a pathway toward new organic electrodes with excellent rate capability and cyclic stability.

Synthesis of a Family of Highly Substituted Porphyrin Thioethers via Nitro Displacement in 2,3,7,8,12,13,17,18-Octaethyl-5,10,15,20-tetranitroporphyrin

A series of highly substituted porphyrin thioethers was synthesized from 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetranitroporphyrin (H₂OETNP). The reactions proceeded via a S_NAr mechanism with a broad range of aromatic thiols in the presence of a base. This is a rapid way to prepare a large variety of meso-substituted porphyrins from only one precursor. Single crystal X-ray analysis revealed that these new porphyrin thioethers are highly distorted, exhibiting conformational properties that are distinctive of both meso-sulfur substitution and steric overcrowding in general. Additionally, denitration of H₂OETNP under basic conditions was investigated, yielding products of stepwise desubstitution. This allowed a comparative X-ray crystallographic study to delineate the successive structural effects of an increasing degree of nitro substitution in the complete series of nitro-substituted octaethylporphyrins.

A theoretical study of methylation and CH/π interactions in DNA intercalation: methylated 1,10-phenanthroline in adenine–thymine base pairs

This work shows that quality is better that quantity to estabilize the intercalation of methylated phen.

Toward a more complete understanding of noncovalent interactions involving aromatic rings

Noncovalent interactions involving aromatic rings, which include π-stacking interactions, anion-π interactions, and XH-π interactions, among others, are ubiquitous in chemical and biochemical systems. Despite dramatic advances in our understanding of these interactions over the past decade, many aspects of these noncovalent interactions have only recently been uncovered, with many questions remaining. We summarize our computational studies aimed at understanding the impact of substituents and heteroatoms on these noncovalent interactions. In particular, we discuss our local, direct interaction model of substituent effects in π-stacking interactions. In this model, substituent effects are dominated by electrostatic interactions of the local dipoles associated with the substituents and the electric field of the other ring. The implications of the local nature of substituent effects on π-stacking interactions in larger systems are discussed, with examples given for complexes with carbon nanotubes and a small graphene model, as well as model stacked discotic systems. We also discuss related issues involving the interpretation of electrostatic potential (ESP) maps. Although ESP maps are widely used in discussions of noncovalent interactions, they are often misinterpreted. Next, we provide an alternative explanation for the origin of anion-π interactions involving substituted benzenes and N-heterocycles, and show that these interactions are well-described by simple models based solely on charge-dipole interactions. Finally, we summarize our recent work on the physical nature of substituent effects in XH-π interactions. Together, these results paint a more complete picture of noncovalent interactions involving aromatic rings and provide a firm conceptual foundation for the rational exploitation of these interactions in a myriad of chemical contexts.

The crystallographic observation of mesitylene–mesitylene and mesitylene–CH2Cl2–mesitylene adducts trapped in an irregular cavity

The mesitylene–mesitylene and mesitylene–CH₂Cl₂–mesitylene adducts can be trapped in the inert cavities. The sp³-CH–π interaction models of these two adducts in the irregular accumulation environment are directly observed.

XH/π (X = C, Si) Interactions in Graphene and Silicene: Weak in Strength, Strong in Tuning Band Structures

The lack of a band gap has greatly hindered the applications of graphene in electronic devices. By means of dispersion-corrected density functional theory computations, we demonstrated that considerable CH/π interactions exist between graphene and its fully (graphane) or patterned partially (C4H) hydrogenated derivatives. Due to the equivalence breaking of two sublattices of graphene, a 90 meV band gap is opened in the graphene/C4H bilayer. The band gap can be further increased to 270 meV by sandwiching graphene between two C4H layers. By taking advantage of the similar SiH/π interactions, a 120 meV band gap also can be opened for silicene. Interestingly, the high carrier mobility of graphene/silicene can be well-preserved. Our theoretical results suggest a rather practical solution for gap opening of graphene and silicene, which would allow them to serve as field effect transistors and other nanodevices.

Synthetic transformations of porphyrins – Advances 2004-2007

Recent developments in the synthesis and transformation of porphyrins and their derivatives are presented. In connection with the Fifth International Conference on Porphyrins and Phthalocyanines (ICPP-5) a survey of current method developments and reactivity studies is made. The review focuses on synthetic advances in porphyrin chemistry. A brief survey of important developments covers selectively the literature from 2004 to late 2007.

Substituent effects on non-covalent interactions with aromatic rings: insights from computational chemistry

Non-covalent interactions with aromatic rings pervade modern chemical research. The strength and orientation of these interactions can be tuned and controlled through substituent effects. Computational studies of model complexes have provided a detailed understanding of the origin and nature of these substituent effects, and pinpointed flaws in entrenched models of these interactions in the literature. Here, we provide a brief review of efforts over the last decade to unravel the origin of substituent effects in π-stacking, XH/π, and ion/π interactions through detailed computational studies. We highlight recent progress that has been made, while also uncovering areas where future studies are warranted.

The CH/π hydrogen bond in chemistry. Conformation, supramolecules, optical resolution and interactions involving carbohydrates

The CH/π hydrogen bond is an attractive molecular force occurring between a soft acid and a soft base. Contribution from the dispersion energy is important in typical cases where aliphatic or aromatic CH groups are involved. Coulombic energy is of minor importance as compared to the other weak hydrogen bonds. The hydrogen bond nature of this force, however, has been confirmed by AIM analyses. The dual characteristic of the CH/π hydrogen bond is the basis for ubiquitous existence of this force in various fields of chemistry. A salient feature is that the CH/π hydrogen bond works cooperatively. Another significant point is that it works in nonpolar as well as polar, protic solvents such as water. The interaction energy depends on the nature of the molecular fragments, CH as well as π-groups: the stronger the proton donating ability of the CH group, the larger the stabilizing effect. This Perspective focuses on the consequence of this molecular force in the conformation of organic compounds and supramolecular chemistry. Implication of the CH/π hydrogen bond extends to the specificity of molecular recognition or selectivity in organic reactions, polymer science, surface phenomena and interactions involving proteins. Many problems, unsettled to date, will become clearer in the light of the CH/π paradigm.