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Singlet and triplet excited state data on two new core-modified expanded porphyrins and their protonated derivatives are reported. Absorption spectral studies indicate a gradual red shift of the absorption bands upon sulfur substitution into the core. The singlet lifetimes for expanded S₃-sapphyrin and S₄-rubyrin decrease steadily relative to STPPH and S₂TPP owing to a higher rate of intersystem crossing. Furthermore, the protonated derivatives of S₃-sapphyrin and S₄-rubyrin encapsulate fluoride ions into their cavities with binding constants of 807 and 48 M⁻¹ respectively. However, the triplet lifetime for S₃-sapphyrin is longer (58.80 μs) than for normal thiaporphyrins (STPPH, 37.45 μs; S₂TPP, 20.96 μs), suggesting that it could be very well suited for photosensitizing triplet oxygen.

The synthesis and X-ray diffraction-based characterization of a texaphyrin-type non-aromatic expanded porphyrin, 13,18,22,27-tetraethyl-14,17,23,26-tetramethyl-20-p-nitrophenyl-3,10,28,29,30,31-hexaazahexacyclo[23.2.1.0^4,9.1^12,15.1^16,19.1^21,24]untriaconta-2, 4, 5, 7, 10,12,14,16,18,-20,22,24(30),25,27-tetradecaene (1), is reported. This Schiff base macrocycle was prepared in good yield via the 1:1 HCl-catalyzed condensation of a tetrapyrrole dialdehyde precursor, (di(5-formyl-4,4'-diethyl-3,3'-dimethyl-2,2'-bipyrrole)-p-nitrophenylmethine), with 1,2-phenylenediamine. Compound 1 was assigned as being a 26 π-electron non-aromatic benzannulene on the basis of both proton NMR and single-crystal X-ray diffraction analyses. The latter studies, in particular, revealed a non-planar macrocyclic structure co-crystallized with a molecule of water. By varying either the diamine used in the cyclization step and/or the substituent in the meso-position of the tetrapyrrolic precursor, a range of other systems analogous to 1 could be obtained. The resulting systems were found to present good stability both in the solid state and in solution.

The chemistry of porphyrin analogues, fully or partially conjugated macrocyclic systems that contain pyrroles but are not naturally occurring substances, is discussed from an historic perspective. Key developments that led to the emergence of this area as a separate discipline within the generalized porphyrin lexicon are highlighted with a view to allowing the reader to understand better the current state of the art in the field.

Syntheses, characterization and spectroscopic studies of meso-mesityl substituted rubyrins are reported. Specifically, it has been shown that these rubyrins behave differently from the meso-phenyl containing rubyrins in their structure. ¹H NMR studies reveal the existence of both planar and inverted isomers in solution in different ratios both in the freebase and protonated forms.

In recent years, the field of porphyrin chemistry has expanded to include several new analogs of the original four pyrrole, carbon-bridged systems. This review traces the development of one such class of new macrocycles, namely Schiff-base porphyrin analogs. The review's focus is on the synthesis and properties of these new Schiff-base macrocycles that for ease of division have been divided into four classes: systems with two pyrrole rings, systems with three pyrrole or heterocyclic rings, systems with four pyrrole or heterocyclic rings, and systems with five or more pyrrole or heterocyclic rings. In addition to the role of metal ions as templating agents in the synthesis of these complexes, the rich coordination chemistry of several of the macrocycles is also discussed. X-ray crystallography has played an important role in determining the structures of many of these Schiff-base porphyrin analogs and many of the available structures have been incorporated into this review. Aromaticity of the macrocycles is discussed and has been evaluated from available electronic and NMR spectra. Finally, several potential applications of these molecules are discussed, briefly.

meso-aryl expanded porphyrins, that can be regarded as real homologues of meso-tetraaryl porphyrins, were prepared by our synthetic protocol under the modified Rothemund-Lindsey conditions. This new class of molecules exhibits interesting spectral, electrochemical, and coordination properties. These promising features are emphasized, with a particular attention on the annulenic properties.

Cyclo[n]pyrroles (n = 6, 7, and 8), are expanded porphyrins that lack bridging meso carbon atoms. They adopt conformations that are near-planar and show features that are consistent with global aromaticity. In previous work, involving studies of cyclo[8]pyrroles, it was found that, in contrast to what is true for porphyrins, reductive per-N-alkylation led to the formation of non-planar products that displayed few signs of extended conjugation. These octa-N-alkylated species could be reoxidized electrochemically to produce dicationic, octa-N-substituted analogues of the starting aromatic cyclo[8]pyrroles. We have now extended this study to cyclo[6]pyrrole, and have found that reductive per-N-methylation can be readily effected using methyl iodide. However, in contrast to what is true in the case of cyclo[8]pyrroles, efforts to obtain the fully N-ethylated or N-benzylated products proved unsuccessful. Moreover, in the case of the hexa-N-methylated cyclo[6]-pyrrole product no viable chemical means of oxidizing it to the putative aromatic dication could be found. However, evidence for the formation of such species was obtained by electrochemical means. The differences between cyclo[6]- and cyclo[8]pyrrole highlight the effect of ring size in mediating the redox and reactivity chemistry within what is otherwise a closely matched pair of porphyrin analogues.

The synthesis and characterization of two 18-crown-6 functionalized analogues of an extensively studied gadolinium texaphyrin derivative, motexafin gadolinium (1, MGd), are reported. These are the monomeric and dimeric species, compounds 2 and 3, respectively. Both crown ether functionalized species proved to be stable at physiological pH and revealed distinct shifts in the UV spectrum when treated with sodium-, potassium-, ammonium- or zinc(II)-salts. Zinc(II) is believed to play a major role regulating apoptosis mechanisms in cancerous cells. Therefore, cytotoxicity studies of 2 and 3 were carried out using the Ramos cell line in the presence and absence of zinc(II).

In recent years much attention has been devoted to expanded macrocyclic chemistry. Nevertheless, while several advancements were achieved in the synthesis of novel expanded porphyrin architectures, not much has been developed in the functionalization of these macrocycles. This report shows the selective replacement of the p-fluorine atoms of meso-pentakis(pentafluorophenyl) N-fused [22]pentaphyrin and meso-hexakis(pentafluorophenyl) [26]hexaphyrin with 4-mercaptopyridine moieties, thus increasing their potential as ligands for coordination chemistry and catalysis or electronic transfer applications striving new synthetic methodologies and a new set of specific applications for this type of compounds.

Over the last two decades the preparation of pyrrole-based receptors for anion recognition has attracted considerable attention. In this regard porphyrins, phthalocyanines and expanded porphyrins have been used as strong and selective receptors while the combination of those with different techniques and materials can boost their applicability in different applications as chemosensors and extracting systems. Improvements in the field, including the synthesis of this kind of compounds, can contribute to the development of efficient, cheap, and easy-to-prepare anion receptors. Extensive efforts have been made to improve the affinity and selectivity of these compounds and the continuous expansion of related research makes this chemistry even more promising. In this review, we summarize the most recent developments in anion binding studies while outlining the strategies that may be used to synthesize and functionalize these type of macrocycles.

In 1960, MacDonald and coworkers introduced a new method for porphyrin synthesis that involved the acid-catalyzed condensation of dipyrrylmethane dialdehydes with $\alpha$,${\alpha }^{\prime }$-diunsubstituted dipyrrylmethanes or the related dicarboxylic acids, followed by an air oxidation. The key bond forming steps entail electrophilic substitution at two pyrrole units with the aldehyde moieties to generate, following elimination of water, a 5,15-dihydroporphyrin or porphodimethene intermediate. Following addition of sodium acetate, or in later procedures zinc acetate, the dihydroporphyrins readily air oxidize to the fully aromatic porphyrin system. This strategy, which parallels chemistry contemporaneously developed by R. B. Woodward at Harvard for the total synthesis of chlorophyll $a$, demonstrated that dipyrrylmethanes were sufficiently stable to be utilized as intermediates in porphyrin syntheses and that porphodimethene formation circumvented acidolytic scrambling reactions that might lead to isomeric porphyrin products. This type of chemistry was later adapted by Johnson, Woodward and others to prepare porphyrin-type systems by a “3 + 1” strategy, or expanded porphyrins by “3 + 2” or other combinations of oligopyrrolic precursors. In recent years, the term “MacDonald condensation” has been increasingly used to describe other types of chemistry involving oligopyrrolic intermediates. Following on from a historical review of this area, guidelines for the identification of MacDonald-type reactions are proposed.

A concise and versatile strategy for the preparation of isoamethyrins is presented. The novel procedure is predicated on the acid catalyzed condensation of a quaterpyrrole and a bipyrrole dialdehyde. As application of this procedure an aryl substituted isoamethyrin has been synthetized and characterized.

Understanding aromaticity is crucial for predicting the molecular properties and reactivity of cyclic $\pi$-conjugated systems. In this review, representative reports on the evaluation of aromaticity via spectroscopic methods in various expanded porphyrin systems are presented. The relationship between the photophysical properties and distinct aromatic characteristics in Hückel aromatic compounds was revealed through notable spectroscopic features exhibited by aromatic expanded porphyrins. Furthermore, modulating the molecular conformation and chemical environment enabled us to distinguish unique Möbius aromatic molecules successfully. These findings provide insight into the elemental molecular properties and aromaticity in expanded porphyrin systems and their potential real-world applications.

We report here the synthesis and structural characterization of a novel expanded Schiff base oligopyrrolic macrocycle TxLH ($i.e.$ compound 2) along with its smaller congener hemi-TxLH ($i.e.$ compound 1). The solid-state structure of TxLH is reminiscent of the shape of a Texas Longhorn${}^{TM}$. It thus defines a new architectural form for porphyrin analogues. The present study thus underscores the potential of using functionalized oligopyrroles as readily accessible molecular building blocks for the construction of structurally non-trivial molecules.

In recent years, much attention has been devoted to synthesizing and preparing novel expanded porphyrin architectures. Here we report the selective substitution of the $p$-fluorine atoms of meso-hexakis(pentafluorophenyl)$N$-confused[26]hexaphyrin with six 4-mercaptopyridine moieties. The preparation methods here described opening an avenue towards the modification and application of these macrocycles in a wide array of applications such as catalysis, sensing, and photonic applications.