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A series of dicarba dithia hexaphyrin(2.0.1.1.1.0)s containing two p -phenylene rings, two thiophene rings, and two pyrrole rings connected via five meso carbons were synthesized by condensing the key precursor, hexapyrrane, which was prepared over a sequence of steps, with the appropriate aromatic aldehyde under acid catalytic conditions followed by alumina chromatographic purification. Detailed one-dimensional (1D) and two-dimensional (2D) NMR studies revealed that the two thiophene rings were inverted and facing outward from the macrocyclic core. Interestingly, one of the inverted thiophene rings adopts a normal orientation in the protonated derivatives of macrocycles generated by addition of trifluoroacetic acid to the appropriate macrocyclic solution. The spectroscopic studies support the non-aromatic nature of macrocycles, and the macrocycles exhibit a distinct sharp band at ∼425 nm along with a broad band in the range of 550-1000 nm, which experienced a red shift with a clear color change in the protonated derivatives. The redox studies showed lower oxidation potentials, indicating their electron-rich nature. The density functional theoretical (DFT) studies showed that the hexaphyrins adopt oval-shaped structures, and time-dependent-DFT (TD-DFT) studies parallelly matched the experimental observations of macrocycles.

The 20π porphyrinoids are immediate higher homologues of 18π porphyrins and differ from porphyrins in aromaticity which in turn affects the structure, properties and chemical reactivities. Research over the years indicated that the 20π porphyrinoids can be stabilized as non-aromatic/anti-aromatic or Mobius aromatic macrocycles using different strategies such as core-modification of porphyrins, non-metal/metal complexation of porphyrins, peripheral modification of porphyrins and expanded porphyrinoids. The structural properties such as aromaticity of the macrocycle can be controlled by choosing the right synthetic strategy. This review will provide an overview of the development in the chemistry of 20π porphyrinoids giving emphasize on the synthesis, structure and electronic properties of these macrocycles which have huge potential for various applications., (© 2022 The Chemical Society of Japan & Wiley-VCH GmbH.)

The first examples of meso-triaryl 22-oxabenzonorroles were synthesized in 18-21% yields by oxidation of appropriate meso-triaryl oxabenzobilane. The key precursors, the meso-triaryl oxabenzobilanes were synthesized readily by treating 16-oxatripyrrane with (1H-indol-3-yl)(p-tolyl)methanol under acid catalyzed conditions. The meso-triaryl 22-oxabenzonorroles were obtained in free base form by following our simple straight-forward synthetic strategy. The X-ray structure obtained for meso-tritolyl 22-oxabenzonorroles revealed that the indole ring was deviated by an angle of 41.27° from the mean plane. The NMR studies supported the presence of diatropic ring current effect as inner NH and CH protons were observed in the upfield region. The absorption spectra of 22-oxabenzonorroles exhibited one strong Soret band and four weak Q-bands. The electrochemical studies revealed that the macrocycles are electron rich and undergo easier oxidations. The DFT and TD-DFT studies were in agreement with the experimental observations and NICS and HOMA values supports the aromatic nature of meso-triaryl oxabenzonorroles., (© 2022 Wiley-VCH GmbH.)

Two examples of nonaromatic m-benziheptaphyrins and two examples of aromatic p-benziheptaphyrins were synthesized by [5+2] condensation of appropriate m-benzi pentapyrrane and p-benzi pentapyrrane respectively and bithiophene diol in CH 2 Cl 2 in the presence of one equivalent of TFA under inert conditions for 30 min followed by oxidation with DDQ in open air for 1 h. The 1 H NMR studies carried out at room temperature as well as at lower temperature indicated the nonaromatic nature of m-benziheptaphyrins with inversion of two thiophene rings and aromatic nature of p-benziheptaphyrins with inversion of one of the thiophene ring. The X-ray structure obtained for one of the p-benziheptaphyrins showed a planar conformation with alignment of one of the thiophene ring away from the macrocyclic inner core but maintained its coplanarity with the mean plane and supported the aromatic nature of the macrocycle. The absorption spectra of m-benziheptaphyrins resembled with the nonaromatic systems and showed two intense bands at 445 nm, 555 nm and a very broad band in the region of 600-1100 nm whereas the p-benziheptaphyrin showed three sharp intense bands at 534 nm, 585 nm and 832 nm due to their aromatic nature. The protonation of m-benziheptaphyrins and p-benziheptaphyrins resulted in significant bathochromic shifts in their absorption maxima and showed strong absorption in NIR region. The electrochemical studies indicated that m- & p-benziheptaphyrins undergo oxidations and reductions easily. DFT and TD-DFT studies were in agreement with the experimental observations., (© 2022 Wiley-VCH GmbH.)

New examples of nonaromatic fused expanded porphyrins containing both pyridine and crown ether moiety as a part of macrocyclic framework were synthesized by condensing pyridine based pentapyrrane with polyether-based diol in CH 2 Cl 2 in the presence of one equivalent of BF 3  ⋅ OEt 2 under inert conditions followed by oxidation with DDQ in open air. The condensation was expected to form pyridine-containing crowned expanded porphyrins but resulted in the formation of fused crowned expanded porphyrins due to intramolecular fusion of two pyrrole nitrogens with two adjacent inverted thiophene carbons as revealed by X-ray crystallography obtained for one of the macrocycle. HRMS and NMR studies supported the formation of fused crowned pyridine containing expanded porphyrins, and the macrocycles showed simple, well-resolved NMR spectra where all resonances were identified easily by 2D NMR spectroscopy. The macrocycles exhibited typical nonaromatic absorption features and showed one broad band with peak maxima at 535 nm and one or two shoulder bands in the higher energy region. The protonation studies resulted in clear colour change from purple to blue and absorption bands experienced bathochromic shifts with a broad band at 662 nm which was extended up to 800 nm. The electrochemical studies revealed that the macrocycles were easier to oxidize but difficult to reduce. DFT studies indicated that the macrocycle attains a very puckered and distorted 'U' shaped structure owing to the flexibility of the crown ether chain and TD-DFT studies corroborated experimental results. The preliminary studies indicated that the macrocycles could be used as colorimetric optical sensor for the detection of Cu 2+ ion., (© 2022 Wiley-VCH GmbH.)

Expanded heteroporphyrins are a class of porphyrin macrocycles containing pyrrole, thiophene, furan, selenophene and other heterocyclic rings that are connected to form an internal ring pathway containing a minimum of 17 atoms and more than 18 delocalized π electrons in their conjugated macrocyclic framework. Considering that expanded heteroporphyrins are large in size, these macrocycles are structurally flexible and prefer to adopt various conformations in which one or more pyrrole(s)/heterocycle(s) tend to be in an inverted conformation and pointed outward from the centre of the macrocyclic core. The inverted expanded heteroporphyrins are divided into two classes as follows: (1) N -inverted expanded heteroporphyrins and (2) hetero-atom inverted expanded heteroporphyrins. Both inverted expanded heteroporphyrins show quite unique features in terms of their structure, aromaticity, and electronic and coordination properties. Sometimes, inverted expanded heteroporphyrins lead to the formation of fused expanded heteroporphyrins because of the intramolecular fusion of the pyrrole "N" with the "C" of the inverted heterocycle ring, which also exhibit unique features compared to inverted expanded heteroporphyrins. In this review, we attempt to describe the synthesis, structure, and aromatic, electronic and coordination properties of inverted and fused expanded heteroporphyrins. This review covers the synthesis, structure and properties of inverted and fused expanded heteroporphyrins containing a combination of pyrrole/heterocycle rings starting with five pyrrole/heterocycle-containing pentaphyrins, and then expanded heteroporphyrins containing six, seven, eight and more pyrrole/heterocyclic rings in their porphyrin macrocyclic framework.

The four pyrrole rings and four meso carbons of tetrapyrrolic porphyrins can be arranged in different ways and the resulting porphyrin isomers exhibit very distinct electronic properties. The extensive research carried out on the porphyrins over the years has revealed that porphyrin can have several possible isomers and some of these have been identified and synthesized. Among the porphyrin isomers synthesized so far, porphycene and N-confused porphyrins have been investigated extensively whereas the other porphyrin isomers such as hemiporphycene, corrphycene and isoporphycene remain underdeveloped because of synthetic difficulties and their inherently unstable nature. Neoporphyrinoids are new members of the porphyrinoid family that were discovered serendipitously in 2011. Neoporphyrinoids are structural analogues of porphyrinoids with a confused pyrrole nitrogen linked to a meso carbon or the adjacent pyrrole carbon. Thus, neoporphyrinoids have an unusual structure in which pyrrole N is a part of a porphyrinoid framework and the lone pair of electrons on nitrogen participate in macrocyclic conjugation. It's been a decade since the discovery and different types of neoporphyrinoids, including regular, contracted and expanded neoporphyrinoids, have been synthesized by rational synthetic methodologies and their spectral, structural, aromatic and coordination properties have been studied. There is huge scope to develop different synthetic routes to produce new types of stable neoporphyrinoids to study their properties and potential applications. This article presents a brief overview of the synthesis, structure and properties of the neoporphyrinoids reported in this decade.

Porphyrins and expanded porphyrins have attracted the attention of chemists for a long time in view of their diverse applications in catalysis; as anion, cation, and neutral substrate receptors; as ligands to coordinate large metal ions; as nonlinear optical materials, MRI contrasting agents, and sensitizers for photodynamic therapy (PDT); and more recently as models for aromaticity (both Hückel and Möbius). A diverse range of synthetic expanded porphyrins containing up to 96π electrons have been reported, and their properties have been exploited for various applications. The present Review is only confined to 22π electron expanded porphyrins containing five pyrrole/heterocyclic rings such as sapphyrins and smaragdyrins. Even though these two macrocycles contain 22π electrons and five pyrrole/heterocyclic rings, they are structurally different. In sapphyrins, the five pyrrole/heterocyclic rings are connected through four meso-carbon bridges and one direct pyrrole-pyrrole bond, whereas in smaragdyrins, the five pyrrole/heterocyclic rings are connected through three meso-carbon bridges and two direct pyrrole-pyrrole bonds. The chemistry of sapphyrins has been well-established in recent years due to the availability of easy and efficient synthetic methods. On the other hand, smaragdyrins are not explored significantly because of their unstable nature. However, recently it was shown that smaragdyrins can be stabilized if one of the pyrrole rings is replaced with a furan ring to afford stable oxasmaragdyrin. The availability of oxasmaragdyrin allowed the exploration of smaragdyrin in recent years. Thus, an attempt has been made in this Review to describe the chemistry of both sapphyrins and smaragdyrins in terms of their synthesis, characterization, metal ion coordination, and anion-recognition properties.

The heteroatom-containing porphyrin analogues or core-modified porphyrins that resulted from the replacement of one or two pyrrole rings with other five-membered heterocycles such as furan, thiophene, selenophene, tellurophene, indene, phosphole, and silole are highly promising macrocycles and exhibit quite different physicochemical properties compared to regular azaporphyrins. The properties of heteroporphyrins depend on the nature and number of different heterocycle(s) present in place of pyrrole ring(s). The heteroporphyrins provide unique and unprecedented coordination environments for metals. Unlike regular porphyrins, the monoheteroporphyrins are known to stabilize metals in unusual oxidation states such as Cu and Ni in +1 oxidation states. The diheteroporphyrins, which are neutral macrocycles without ionizable protons, also showed interesting coordination chemistry. Thus, significant progress has been made in last few decades on core-modified porphyrins in terms of their synthesis, their use in building multiporphyrin arrays for light-harvesting applications, their use as ligands to form interesting metal complexes, and also their use for several other studies. The synthetic methods available in the literature allow one to prepare mono- and diheteroporphyrins and their functionalized derivatives, which were used extensively to prepare several covalent and noncovalent heteroporphyrin-based multiporphyrin arrays. The methods are also developed to synthesize different hetero analogues of porphyrin derivatives such as heterocorroles, heterochlorins, heterocarbaporphyrinoids, heteroatom-substituted confused porphyrins, and so on. This Review summarizes the key developments that have occurred in heteroporphyrin chemistry over the last four decades.

New multiple photosynthetic reaction centers were constructed from cyclophosphazene decorated multiporphyrin chromophores and a fulleropyrrolidine having a pyridine ligand (FPY). The excited state electron transfer in the self-assembled donor-acceptor assembly was investigated by using steady state absorption and emission, time-resolved emission spectroscopy and nanosecond laser flash photolysis. The effect of metal (Zn(2+)) coordination to porphyrin units in the multiporphyrin arrays on cyclophosphazine scaffold (P3N3Zn) was studied by comparing with metal free porphyrin assembly on a cyclophosphazene scaffold (P3N3). In P3N3Zn, the decrease of absorption and fluorescence intensity and the lowering of the amplitude of longer fluorescence lifetime with increase of FPY concentration reflect the formation of a ground state complex with an association constant of ∼14,910 M(-1). When compared to the metal-free complex P3N3, the metal-coordinated derivative P3N3Zn exhibited shortening of the singlet and triplet state lifetimes and lowering of the singlet and triplet quantum yields. The cause of the decrease of the triplet quantum yields by insertion of zinc metal is discussed along with the possible non-planarity of the porphyrin ring. From the fluorescence lifetime measurements for the P3N3Zn-FPY mixture, it is proposed that self-assembly of the donor-acceptor complex leads to charge separated species with a rate constant of 7.1 × 10(9) s(-1). The decrease of triplet state intensity and lifetime of the P3N3Zn in the P3N3Zn-FPY complex from the nanosecond transient absorption studies support the occurrence of intermolecular electron transfer in the triplet state.

Condensation of dibenzofuran based tripyrrane with dipyrroethene diol under acid catalyzed porphyrin forming conditions resulted in the formation of dibenzofuran embedded calix pentaphyrins with two meso‐sp3 carbons instead of expected fully conjugated dibenzofuran (DBF) embedded pentaphyrins. Three examples of DBF embedded calix pentaphyrins have been synthesized by adopting the [3+2] condensation methodology and characterized by various spectroscopic and theoretical methods. The NMR studies that include COSY, NOESY, HMBC and HSQC clearly confirmed the molecular structures of DBF embedded bis‐(calix)‐pentaphyrins. The optimized structures showed that the DBF embedded bis‐(calix)‐pentaphyrin macrocycles adopted figure eight conformation due to presence of two sp3 carbon atoms (C1 and C22) at meso positions which obstructed the conjugation throughout the macrocycle. The absorption spectra of macrocycles showed non‐aromatic features with a sharp strong band at 480 nm and a broad band in the region of 600–800 nm which were significantly red shifted with distinct colour change in protonated derivatives of DBF embedded bis‐(calix)‐pentaphyrins. [ABSTRACT FROM AUTHOR]

[Display omitted] • Porphycenes are structural isomers of porphyrins. • Porphycenes contain two bipyrrolic units connected via four meso -carbons. • The small rectangular-shaped inner cavity and strong intramolecular hydrogen bonding inside the porphycene core hinder the formation of coordination complexes. • The substituents at meso - and β -pyrrole carbons change the rectangular-shaped cavity and reduce intramolecular hydrogen bonding in porphycenes. • Porphycenes form coordination complexes like porphyrins but not as readily as porphyrins. Porphycenes are one of the most explored porphyrin isomers, containing two bipyrrolic units linked by four meso carbons and absorb and emit more strongly in the visible region than porphyrins. Porphyrins are highly flexible ligands that bind across the periodic table with various metals, non-metals, and metalloids. On the other hand, porphycenes, do not form coordination complexes as easily as porphyrins due to the strong intramolecular hydrogen bonding in the core and the rectangular cavity shape of the core. However, with the appropriate substituents at β -pyrrole or meso -carbons or at both the sites, the intramolecular hydrogen bonding inside the core weakens and the porphycene core adopts suitable cavity shape to form unique coordination complexes whose physicochemical properties are quite different from coordination complexes of porphyrins. Although the coordination chemistry of porphycenes has been investigated for several years since 1986, but only in recent times, there has been very significant developments in the coordination chemistry of porphycenes. In this review, an attempt has been made to provide a comprehensive overview of the detailed synthesis, structure, and properties of coordination complexes of porphycenes and compare the properties with the coordination complexes of the porphyrins. It has been shown that the presence of substituents on the β -pyrrole carbons and/or meso -carbons helps to change the electronic properties and tune the shape of the cavity from rectangular to nearly square planar so that these macrocycles can easily form the coordination complexes. We hope that this review will be helpful to further developments in the coordination chemistry of porphycenes in the near future. [ABSTRACT FROM AUTHOR]

New examples of nonaromatic fused expanded porphyrins containing both pyridine and crown ether moiety as a part of macrocyclic framework were synthesized by condensing pyridine based pentapyrrane with polyether‐based diol in CH2Cl2 in the presence of one equivalent of BF3 ⋅ OEt2 under inert conditions followed by oxidation with DDQ in open air. The condensation was expected to form pyridine‐containing crowned expanded porphyrins but resulted in the formation of fused crowned expanded porphyrins due to intramolecular fusion of two pyrrole nitrogens with two adjacent inverted thiophene carbons as revealed by X‐ray crystallography obtained for one of the macrocycle. HRMS and NMR studies supported the formation of fused crowned pyridine containing expanded porphyrins, and the macrocycles showed simple, well‐resolved NMR spectra where all resonances were identified easily by 2D NMR spectroscopy. The macrocycles exhibited typical nonaromatic absorption features and showed one broad band with peak maxima at 535 nm and one or two shoulder bands in the higher energy region. The protonation studies resulted in clear colour change from purple to blue and absorption bands experienced bathochromic shifts with a broad band at 662 nm which was extended up to 800 nm. The electrochemical studies revealed that the macrocycles were easier to oxidize but difficult to reduce. DFT studies indicated that the macrocycle attains a very puckered and distorted 'U' shaped structure owing to the flexibility of the crown ether chain and TD‐DFT studies corroborated experimental results. The preliminary studies indicated that the macrocycles could be used as colorimetric optical sensor for the detection of Cu2+ ion. [ABSTRACT FROM AUTHOR]

Core-modified porphyrinoids or heteroporphyrinoids are a class of porphyrinoids in which one or more core pyrrole nitrogen atom(s) of the macrocycles are replaced predominantly by group-16 atoms such as O, S, Se, and Te. Telluraporphyrinoids are distinct and interesting from the rest of the chalcogenide atom(s) containing porphyrinoids owing to the larger size of Te and the consequent properties arising from it. The telluraporphyrinoid chemistry is only sporadically investigated and the developments are rather slow compared to the other lighter group-16 atom containing porphyrinoids. This perspective presents a concise overview of the developments that have taken place in the field of telluraporphyrinoid chemistry since its inception and includes various aspects such as the synthesis, structure, reactivity, and properties of tellurium-containing porphyrins and other related porphyrinoids such as vacataporphyrins, carbaporphyrins, calixphyrins, and expanded porphyrins. [ABSTRACT FROM AUTHOR]

A series of new [20]dioxahomoporphyrins have been synthesized by [2+2] condensation of (but-2-ene-2,3-diyldifuran- 2,5-diyl)bis(p-methoxyphenylmethanol) with appropriate meso-aryldipyrromethanes under mild acid-catalyzed conditions. The X-ray structure determined for one of the dioxahomoporphyrins revealed that the macrocycle is significantly distorted and the two furan rings are completely out-of-plane from the mean plane. The [20]dioxahomoporphyrin macrocycles are stable and non-aromatic, and have been characterized in detail by HRMS, 1D and 2D NMR spectroscopy, UV/Vis spectrophotometry and electrochemical techniques. The iodofunctionalized [20]dioxahomoporphyrin was used to synthesize a covalently linked diphenylethyne-bridged [20]dioxahomoporphyrin- porphyrin dyad by coupling with an ethynyl-functionalized porphyrin under mild copper-free Pd0 catalytic conditions. The metallation of the porphyrin macrocycle of the [20]dioxahomoporphyrin- porphyrin dyad was carried out by treating the dyad with the appropriate metal salt under standard conditions and the resulting [20]dioxahomoporphyrin-metalloporphyrin dyads were characterized by various spectral and electrochemical techniques. The results of the studies indicated that in the dyads the dioxahomoporphyrin and porphyrin/metalloporphyrin units interact weakly and retain their individual features. [ABSTRACT FROM AUTHOR]

Cyclotriphosphazene and cyclotetraphosphazene appended with six and eight sapphyrin units, respectively, were prepared by treating N3P3Cl6 and N4P4Cl8 with the appropriate equivalents of 5,10,15-tri( p-tolyl)-20-(4-hydroxyphenyl)-25,27,29-trithiasapphyrin in tetrahydrofuran (THF) in the presence of Cs2CO3 at temperatures of 0 to 60 °C for 8-12 h. The two multi-expanded porphyrin assemblies were soluble in common organic solvents, and their identities were confirmed by their corresponding molecular ion peak in the MALDI-TOF mass spectra. 1D and 2D NMR spectroscopic techniques were used to deduce the molecular structures of the mult-expanded porphyrin assemblies. Absorption spectral studies showed that the band positions of the multisapphyrin assemblies were similar to that of the monomeric sapphyrin, but the extinction coefficients were three- to fourfold higher than that of the monomeric sapphyrin. The multisapphyrin assemblies are not very stable under redox conditions. [ABSTRACT FROM AUTHOR]

Expanded dithiacalixphyrins with the N2S2 core containing two sp3 and three sp2meso-carbons have been prepared by condensation of one equivalent of butene-2,3-diyl-bisthiophene-2,5-diyl-bis(p-methoxyphenylmethanol) with one equivalent of 5,5′-dialkyldipyrromethane under mild acid catalyzed conditions in decent yields. The expanded dithiacalixphyrins were characterized by HR-MS, 1D and 2D NMR techniques and the structure of one of the expanded dithiacalixphyrin macrocycles was solved by X-ray crystallography. The crystal structure analysis indicated that the macrocycle is highly distorted and attains a boat shaped structure. The expanded thiacalixphyrins showed a specific sensing ability for F− ions over other anions as judged from absorption, NMR and mass spectral studies. [ABSTRACT FROM AUTHOR]

A simple, one-step, supramolecular strategy was adopted to synthesize SnIV-porphyrin-based axially bonded triads and higher oligomers by using meso-pyridyl SnIV porphyrin, meso-hydroxyphenyl-21,23-dithiaporphyrin, and RuII porphyrin as building blocks and employing complementary and non-interfering SnIVO and RuII ⋅⋅⋅N interactions. The multiporphyrin arrays are stable and robust and were purified by column chromatography. 1H, 1H-1H COSY and NOESY NMR spectroscopic studies were used to unequivocally deduce the molecular structures of SnIV-porphyrin-based triads and higher oligomers. Absorption and electrochemical studies indicated weak interaction among the different porphyrin units in triads and higher oligomers, in support of the supramolecular nature of the arrays. Steady-state fluorescence studies on triads indicated the possibility of energy transfer in the singlet state from the basal SnIV porphyrin to the axial 21,23-dithiaporphyrin. However, the higher oligomers were weakly fluorescent due to the presence of heavy RuII porphyrin unit(s), which quench the fluorescence of the SnIV porphyrin and 21,23-dithiaporphyrin units. [ABSTRACT FROM AUTHOR]

Abstract: Two covalently linked diphenyl ethyne bridged unsymmetrical dyads containing porphyrin and BF2–oxasmaragdyrin and Zn(II)porphyrin and BF2–oxasmaragdyrin units and one covalently linked triad containing Zn(II)porphyrin, porphyrin and BF2–oxasmaragdyrin units were synthesized by coupling appropriate functionalized macrocycles under Pd(0) coupling reaction conditions. The dyads and triad were freely soluble in common organic solvents and confirmed by ES-MS spectra. 1D and 2D NMR techniques were used to characterize the dyads and triad. Absorption and electrochemical studies of dyads and triad showed the overlapping features of the constituted macrocycles indicating that the macrocycles retain their basic features in the dyads and triad. The BF2–oxasmaragdyrin absorbs at lower energy and emits strongly in the visible region compared to porphyrin/Zn(II)porphyrin. Thus, BF2–oxasmaragdyrin acts as energy acceptor and porphyrin/Zn(II) porphyrin act as energy donor in dyads and triad. The steady state and time-resolved fluorescence studies supported an efficient energy transfer from porphyrin/Zn(II)porphyrin to BF2–oxasmaragdyrin unit in dyads and triad. [Copyright &y& Elsevier]

Abstract: Cyclotriphosphazene and cyclotetraphosphazene appended with six and eight covalently linked porphyrin–ferrocene conjugates respectively were synthesized by treating N3P3Cl6 and N4P4Cl8 with appropriate equivalents of ferrocene linked porphyrin containing meso-hydroxyphenyl group in THF in the presence of Cs2CO3 followed by column chromatographic purification. NMR and absorption studies indicated a weak interaction between adjacent porphyrin–ferrocene conjugates. Electrochemical studies supported electrochemical equivalence of ferrocenyl and porphyrinyl moieties in these multi-porphyrin–ferrocene conjugate assemblies. The fluorescence studies showed significant quenching of porphyrin fluorescence due to photo-induced electron transfer from ferrocene to singlet state of porphyrin unit in these assemblies. [Copyright &y& Elsevier]

Four axial-bonding type Al(iii) porphyrin based dyads, containing thiaporphyrins with N3S 1 and N2S22 cores and expanded thaiporphyrins with N2S33 and N2S44 cores, were synthesised by treating [(TPP)AlIIIOH] with the corresponding mono-functionalised meso-4-hydroxyphenyl thiaporphyrin or expanded thiaporphyrin building blocks in benzene at refluxing temperature. The stable dyads 1–4 are freely soluble in common organic solvents and characterized by mass, 1D and 2D NMR, absorption, electrochemical and fluorescence techniques. 1D and 2D NMR studies unambiguously confirmed the dyads. The absorption and electrochemical studies show weak interaction between the two macrocycles in dyads and the constituted macrocycles in dyads mostly retain their characteristic individual features. The steady state fluorescence studies indicate a decrease in the quantum yield of Al(iii) porphyrin unit in dyads 1–4 and invoked the possibility of singlet–singlet energy transfer from the Al(iii) porphyrin unit to the N3S porphyrin unit in dyad 1 and N2S2 porphyrin unit in dyad 2. Structural information of these dyads in their ground (S0) state are generated by applying density functional theory (DFT) based quantum chemical calculations. Excited state calculations are carried out following time dependent density functional theory (TD-DFT) and UV-Vis spectra of these dyads are simulated in the Soret band region. [ABSTRACT FROM AUTHOR]

The hexa-coordinated rhenium(l) tricarbonyl complexes of 5,10,15,20-tetraphenyl-21-thiaporphyrin 1 and 5,10,15,20-tetraphenyl-21-oxaporphyrin 2 have been synthesized by thermal reaction of corresponding free base porphyrin with Re2(CO)10. The compounds 1 and 2 are characterized by HR-MS mass, 1H, and 13C NMR, FTIR, UV-vis, and electrochemical techniques and the structures are determined by X-ray single crystal analysis. The X-ray analysis revealed different coordination behavior of Re(CO)3 with 21-thiaporphyrin and 21 -oxaporphyrin. Interestingly, the Re(CO)3 coordinates to two of the three inner nitrogens and one sulfur instead of three inner nitrogens as generally expected to produce unique compound 1 whereas it coordinates to three inner nitrogens but not with furan oxygen to form compound 2. The 2I-thiaporphyrin ring is more distorted in compound 1 compared to 21-oxaporphyrin ring in compound 2 on complexation with Re(CO)3. The presence of three carbonyl groups in compounds 1 and 2 are verified by 13CNMR and IR spectroscopy. The absorption spectra of compounds 1 and 2 showed ill-defined Q;bands along with broad Soret band and the extinction coefficients are much lower than their corresponding free base porphyrins. The compounds 1 and 2 showed two reversible porphyrin ring based reductions supporting their electron deficient nature. The compound 1 is very stable under protonation conditions, and tlie protonation occurs at the uncoordinated pyrrole ring whereas the compound 2 undergoes decomplexation under same conditions. Furthermore, compound 1 showed the flmdonal behavior in coordination mode of binding in solution. [ABSTRACT FROM AUTHOR]

Abstract: Boron-dipyrromethenes (BODIPY) containing oxypyridine substituents at 3- and 3,5-positions and metalloporphyrins (Zn(II), Ru(II)) were used to synthesize four non-covalent BODIPY–metalloporphyrin dyads and four BODIPY–metalloporphyrin triads assembled using metal–pyridine ‘N’ interaction. The formation of BODIPY–metalloporphyrin assemblies was confirmed by 1D and 2D NMR methods and X-ray crystal structure obtained for one of the BODIPY–metalloporphyrin dyad. In 1H NMR, the signals of oxypyridine group(s) of BODIPY unit showed significant upfield shifts supporting the coordination of oxypyridine group of BODIPY unit to metalloporphyrin unit. The NMR study also indicated that Zn(II) porphyrin forms relatively weak BODIPY–Zn(II) porphyrin conjugates, whereas Ru(II) porphyrin forms strong BODIPY–Ru(II) porphyrin conjugates. The X-ray structure solved for BODIPY–Zn(II)porphyrin dyad revealed that the Zn(II) porphyrin coordinated to the BODIPY unit obliquely and the angle between the Zn(II) porphyrin and the pyridyl ring is 70°. The absorption properties of stable BODIPY–Ru(II) porphyrin conjugates showed the overlapping absorption features of both the components and the fluorescence studies indicated that the BODIPY unit emission was significantly quenched on coordination with RuTPP(CO) unit. The electrochemical studies exhibited the features of both BODIPY and metalloporphyrin units in dyads and traids. [Copyright &y& Elsevier]

We report the synthesis of first examples of BF2 and B(OR)2 complexes of oxasmaragdyrin, the expanded core-modified porphyrin, in decent yields under very simple reaction conditions at room temperature. The boron complexation of oxasmaragdyrin alters the electronic properties of the macrocycle significantly as evident by various spectroscopic techniques. Our preliminary studies indicated that the B(OH)2-smaragdyrin complex can act as a selective neutral fluoride ion sensor. [ABSTRACT FROM AUTHOR]

Two examples of supramolecular tetrads containing Sn(IV) porphyrin, expanded thiaporphyrins such as sapphyrin and rubyrin, and Ru(II) porphyrin assembled using non-interfering cooperative tin(IV)…oxygen and ruthenium(II)…nitrogen coordination properties are described. These are the first examples in which the expanded porphyrins are used as axial ligands. The tetrads were prepared by adopting one step as well as stepwise approaches. In a one pot approach, the mono meso-pyridyl dihydroxy Sn(IV) porphyrin, meso-hydroxyphenyl expanded thiaporphyrin, and Ru(II) porphyrin were reacted in benzene under refluxing conditions followed by column chromatographic purification on alumina to afford tetrads. In a stepwise approach, the axial bonding type of triads containing Sn(IV)porphyrin as central unit and expanded thiaporphyrins as axial ligands were synthesized first by reacting meso-pyridyl dihydroxy Sn(IV) porphyrin with meso-hydroxyphenyl expanded thiaporphyrin in benzene at refluxing temperature. In the next step, the triads were reacted with Ru(II) porphyrin under mild reaction conditions to afford tetrads in decent yields. Both methods worked efficiently and produced stable, soluble tetrads in decent yields. One-dimensional (1D) and two-dimensional (2D) NMR techniques were used to confirm the identity of these novel tetrads. Absorption and electrochemical studies indicated that the components in tetrads interact weakly and retain their individual characteristic features. The steady state photophysical studies revealed that the quantum yield of Sn(IV) porphyrin in tetrads was reduced significantly because of non-radiative decay pathways operating in these systems. [ABSTRACT FROM AUTHOR]

The thiaporphyrin building blocks with N3S and N2S2 cores containing one hydroxyphenyl functional group at the meso position were synthesized by adopting the unsymmetrical thiophene diol method. These monohydroxy thiaporphyrins were used to construct the first examples of axial bonding type Sn(IV) porphyrin triads in which Sn(IV) porphyrin acts as basal unit and the two thiaporphyrin units as axial ligands by treating with SnTTP(OH)2 in benzene at refluxing temperature. The axial bonding type triads were confirmed by mass, 1D and 2D NMR studies. The absorption and electrochemical studies support weak ground state interaction among the porphyrin subunits within the porphyrin triads. The fluorescence studies indicate there is a possibility of energy transfer at the singlet state from basal Sn(IV) porphyrin unit to axial thiaporphyrin units. [ABSTRACT FROM AUTHOR]

The tetrafunctionalized AB3-type porphyrin building blocks containing two different types of functional groups with N4, N3O, N3S, and N2S2 porphyrin cores were synthesized by following various synthetic routes. The AB3-type tetrafunctionalized N4 porphyrin building block was synthesized by a mixed condensation approach, the N3S and N30 porphyrin building blocks by a mono-ol method, and N2S2 porphyrin building block by an unsymmetrical diol method. The tetrafunctionalized porphyrin building blocks were used to synthesize monofunctionalized porphyrin tetrads containing two different types of porphyrin subunits by coupling of 1 equiv of tetrafunctionalized N4, N3O, N3S, and N2S2 porphyrin building block with 3 equiv of monofunctionalized ZnN4 porphyrin building block under mild copper-free Pd(O) coupling conditions. The monofunctionalized porphyrin tetrads were used further to synthesize unsymmetrical porphyrin pentads containing three different types of porphyrin subunits by coupling 1 equiv of monofunctionalized porphyrin tetrad with 1 equiv of monofunctionalized N2S2 porphyrin building blocks under the same mild Pd(O) coupling conditions. The NMR, absorption, and electrochemical studies on porphyrin tetrads and porphyrin pentads indicated that the monomeric porphyrin subunits in tetrads and pentads retain their individual characteristic features and exhibit weak interaction among the porphyrin subunits. The steady state and time-resolved fluorescence studies support an efficient energy transfer from donor porphyrin subunit to acceptor porphyrin subunit in unsymmetrical porphyrin tetrads and porphyrin pentads. [ABSTRACT FROM AUTHOR]

Abstract: The absorption and fluorescence properties of a series of meso-thienylporphyrins with different porphyrin cores (N4, N3O, N3S and N2S2 cores) were studied and compared with the corresponding meso-tetraarylporphyrins. The replacement of six-membered phenyl groups with five-membered thienyl groups at meso-positions resulted in red shifts and broadening of absorption and emission bands, low quantum yields and decreased S1 state lifetimes and the maximum effects were observed for meso-tetrathienylporphyrin with N2S2 porphyrin core. Similar observations were noted for the dications of meso-thienylporphyrins compared to the dications of the corresponding meso-tetraarylporphyrins. These results suggest that the replacement of six-membered aryl group with five-membered thienyl groups at meso-positions, the electronic properties of the porphyrin were altered significantly. [Copyright &y& Elsevier]

A rapid synthetic route has been developed to synthesize mono- and trifunctionalized 21-thia and 21-oxaporphyrin systems using simple precursors such as 2[α-(aryl)-α-hydroxymethyl] thiophene (thiophene mono-ol) and 2[α-(aryl)-α-hydroxymethyl] furan (furan mono-ol), respectively. Condensation of one equivalent of thiophene or furan mono-ol with two equivalents of aryl aldehyde and three equivalents of pyrrole under porphyrin forming conditions followed by column chromatography resulted in functionalized 21-thia or 21-oxaporphyrins. To synthesize monofunctionalized porphyrins, the mono-ol containing the functionalized aryl group was used. The functionalized aldehydes were used to synthesize trifunctionalized porphyrins. The mono-ol method is versatile and applicable to synthesize mono- and trifunctionalized 21-thia and 21-oxaporphyrins containing functional groups such as iodophenyl, ethynylphenyl, hydroxyphenyl, bromophenyl, and pyridyl groups. The monofunctionalized porphyrin building blocks containing iodophenyl and ethynylphenyl groups were used further to synthesize four unsymmetrical covalent porphyrin dimers containing two different porphyrin cores such as N3S-N4, N3O-N4, and N3S-N3O bridged via diaryl ethyne group and one symmetrical phenylethyne bridged dimer containing two N3S cores. A preliminary photophysical study on these dimers indicated a possibility of energy transfer from one subunit to another. We also demonstrated the use of trifunctionalized porphyrins in the synthesis of two noncovalent unsymmetrical porphyrin tetramers containing one N3S and three N4 porphyrin subunits. [ABSTRACT FROM AUTHOR]

A new method has been developed to synthesize 21,23-dithiaporphyrins having one pyridyl group at the meso position. The method required easily available unknown precursors and the condensation resulted in mono meso-pyridyl 21,23-dithiaporphyrins as single products in 8–11% yield. Two of the three mono meso-pyridyl N2S2 porphyrins were used to synthesize non-covalent unsymmetrical porphyrin dimers containing one N2S2 and one N4 porphyrin cores. [Copyright &y& Elsevier]

A series of β-pyrrole and β-thiophene substituted porphyrins with N2S2 and N3S porphyrin cores were synthesized and characterized. The introduction of substituents at β-pyrrole and β-thiophene carbons resulted in significant shifts in 1H NMR, absorption and fluorescence maxima. These effects were attributed to alteration of the porphyrin ring current caused by substituents at β-positions. [Copyright &y& Elsevier]

A series of meso-furyl porphyrins with four different porphyrin cores (N4, N3S, N2S2 and N3O) were synthesized and characterized. The comparison of NMR, optical and fluorescence properties of meso-furyl porphyrins with porphyrins with six-membered aryl groups indicates that electronic properties of porphyrins were changed drastically on the introduction of furyl groups at meso positions. The maximum shifts in spectral bands were observed for meso-furyl porphyrins with N2S2 core. On protonation, the absorption bands of meso-furyl porphyrins were further red shifted. All these changes were ascribed to the possibility of more planarity of the meso-furyl porphyrins due to the small size of the furyl groups which results in extending the π-delocalisation of the porphyrin ring in to the furyl groups. [Copyright &y& Elsevier]

We report the unusual formation of thiaisoporphyrins containing bridging sp3meso carbon between two pyrroles when 21-thiaporphyrins were reacted with PhBCl2 in dry toluene at reflux temperature. [ABSTRACT FROM AUTHOR]

• Rhenium forms complexes with different types of porphyrinoids. • Rhenium exhibits variable oxidation states in porphyrinoid complexes. • Fluxional behavior was observed in rhenium complexes of porphyrin and core-modified porphyrins. • Rhenium porphyrinoids are luminescent. • Rhenium-oxo complexes exhibit catalytic activity. Rhenium coordination complexes offer a wide range of applications in various fields and have been emerged as a profound research area in recent years. Rhenium, being a group 7 congeners, shows rich coordination chemistry with different porphyrinoid ligands and formed complexes with rhenium metal stabilized in various oxidation states such as +I, +II,+III, +V and, +VII. In this article, we provide a comprehensive overview of the state-of-the-art rhenium porphyrinoids by detailing their synthesis, characterization, and reactivity studies. The historical overview of rhenium complexes of porphyrin, porphycene, N-confused porphyrin, N-fused porphyrin, core-modified porphyrins, corrole, triphyrin, and expanded porphyrin systems are described, and in each case, the distinct role of the porphyrinoid ligand in stabilizing the corresponding rhenium complex as well as their reactivity are discussed. The high and low-valent rhenium porphyrinoid complexes helped to understand the rhenium-heteroatom (Re–X) bonding features, fluxional behaviour, Re-Re multiple bond formation, and their luminescent properties. Due to their extraordinary features, the rhenium porphyrinoids have great potential applications in various fields, including modern-day materials and catalysis research. We hope that this article will be helpful to further design and develop new rhenium porphyrinoids in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • Boron complexes of porphyrinoids contain boron in + III oxidation state. • Mono- and di-boron complexes of porphyrinoids exhibit unusual coordination modes and stereochemical arrangements. • Boron complexes of expanded porphyrinoids show excellent photophysical properties. • Boron porphyrinoids display interesting redox properties. • BF 2 -oxasmaragdyrin complexes are used in Dye-sensitized Solar cells (DSSC) and Photothermal Therapy (PTT) studies. Boron being a small atom, its coordination chemistry with different porphyrinoids is very unique and unusual compared to coordination chemistry of porphyrinoids with transition metals and other main group elements. One such unique feature is the coordination of more than one boron with the porphyrinoid ligand. The mono- and diboron(III) complexes of porphyrinoids showed distinct coordination variations and exhibited exciting photophysical and redox properties. In this review, we present an overview of the synthesis, structure, and spectral properties of various boron complexes of porphyrinoids that include porphyrins, porphycenes, N-confused and N-fused porphyrins, corroles, triphyrins, expanded porphyrins, and calixphyrins. We described a comparison-based aforementioned boron porphyrinoids addressing their structural varieties, unexpected chemistry associated at both the boron centre, and the porphyrinoid ligand, and possible reasoning behind their unusual coordination chemistry. Interestingly, the usage of the boron porphyrinoids for practical applications has been limited till now. Only the B(III) complexes of 25-oxasmaragdyrins have been explored for ion sensing and photothermal therapy of cancer, whereas some BF 2 complexes of calix[16]phyrin, and N-confused calix[8]phyrin have been used for light-harvesting properties, which were also briefly discussed in this review. Thus, we anticipate that the present review article would encourage the porphyrin fraternity to design the new examples of boron porphyrinoids and explore their unrealized potential in modern-day research fields such as developing photocatalysts for organic transformations and solar energy conversion or nano-assemblies for theragnostic agents in clinical applications. [ABSTRACT FROM AUTHOR]

Abstract: A series of triazole bridged BODIPY-conjugates were synthesized under click reaction conditions. The 3-azido BODIPY was generated in situ by treating 3-bromo BODIPY with NaN3 in CH3CN at room temperature for 60 min and reacted with appropriate ethynyl containing chromophore/redox active unit, such as ferrocene, BODIPY, Zn(II) porphyrin, 21,23-dithiaporphyrin, BF2-smaragdyrin in the presence of CuI/DIPEA in THF/CH3CN solvent. The conjugates were purified by column chromatography and obtained pure compounds in 45–50% yields. The conjugates were characterized by HR-MS, 1D, 2D, 19F and 11B NMR and X-ray crystallography for BODIPY-ferrocene conjugate. Absorption and electrochemical studies showed features of both the moieties present in the conjugates and also support interaction between the two moieties in the conjugates. The fluorescence studies supported an efficient energy transfer from BODIPY unit to BF2-smaragdyrin unit in BODIPY–BF2-smaragdyrin conjugate but the energy transfer was not efficient in BODIPY–Zn(II) porphyrin and BODIPY–21,23-dithiaporphyrin conjugates. [Copyright &y& Elsevier]

• Expanded porphyrins are a class of porphyirinoid macrocycles possessing more than four pyrrole/other heterocyclic rings and multiple meso -carbon bridges in their conjugated structural frame-work. • Expanded porphyrins are different from tetrapyrrolic porphyrin macrocycles in having larger π-electron circuit, larger sized macrocyclic core and are capable of exhibiting Hückel and Möbius topologies. • The coordination chemistry of expanded porphyrins is distinct compared to porphyrins as they are capable of binding larger sized metal ions and also more than one metal ion in their macrocyclic core. • In this review article, we summarize the syntheses, structure and properties of coordination complexes of expanded porphyrins spanning pentaphyrins (including sapphyrins and smaragdyrins), hexaphyrins (including rubyrins, amethyrins, and isoamethyrins), heptaphyrins, octaphyrins, nonaphyrins, decaphyrins and larger macrocycles containing different types of linkages between interconnected pyrrole units. Expanded porphyrins are a class of porphyirinoid macrocycles possessing more than four pyrrole/other heterocyclic rings and multiple meso -carbon bridges in their conjugated structural frame-work. Expanded porphyrins are different from tetrapyrrolic porphyrin macrocycles in having larger π-electron circuit, larger sized macrocyclic core and are capable of exhibiting Hückel and Möbius topologies. The coordination chemistry of expanded porphyrins is distinct compared to porphyrins as they are capable of binding larger sized metal ions and also more than one metal ion in their macrocyclic core. In this review article, we summarize the syntheses, structure and properties of coordination complexes of expanded porphyrins spanning pentaphyrins (including sapphyrins and smaragdyrins), hexaphyrins (including rubyrins, amethyrins, and isoamethyrins), heptaphyrins, octaphyrins, nonaphyrins, decaphyrins and larger macrocycles containing different types of linkages between interconnected pyrrole units. [ABSTRACT FROM AUTHOR]

The dibenzofuran/dibenzothiophene-based nonaromatic hybrid macrocycles, exhibiting the features of both contracted macrocycles, subporphyrins and triphyrins, have been synthesized under simple reaction conditions using readily available precursors. The monoanionic new macrocyclic ligands with three donor atoms, such as two pyrrole nitrogens and one dibenzofuran oxygen or dibenzothiophene sulfur, readily form Re(I) complexes. [ABSTRACT FROM AUTHOR]

Highlights: [•] BODIPY-porphyrin conjugates are ideal models to study energy transfer at singlet state. [•] BODIPY-porphyrin conjugates were synthesized due to their complementary optical properties. [•] In conjugates, BODIPY acts as energy donor and porphyrin acts as energy acceptor. [•] Sequential energy transfer and electron transfer were studied in BODIPY-porphyrin-fullerene triads. [•] BODIPY-porphyrin based photonic wires and optoelectronic gates were synthesized. [Copyright &y& Elsevier]

An unusual formation of 21-oxacorrole from 21-oxaporphyrin by concomitant elimination of a meso-aryl group and ring contraction is reported. [ABSTRACT FROM AUTHOR]

Meso-tetrasubstituted Mg(ll) porphyrins containing six membered phenyl groups (MgTPP) and five membered thienyl (MgTThP) and furyl groups (MgTFP) were synthesized and structuralty characterized, and the effects of meso- substituents on electronic properties were studied using NMR, absorption, fluorescence spectroscopy, and electrochemical studies. Density functional theory (DFT) calculations were carried out to correlate with experimental observations. The three Mg(lI) porphytins MgTPP, MgTThP, and MgTFP were crystallized as hexa-coordinate systems with Mg(Il) ion in the center of the porphyrin plane and having two tetrahydrofuran molecules as axial ligands. The X-ray studies clearly showed that the meso-furyl groups adopt a conformation in which they are more in-plane with the porphyrin plane whereas the thienyl and phenyl groups prefer an orthogonal arrangement with respect to the porphyrin plane. This arrangement of meso-substituents with the porphyrin plane helps in the enhancement of porphyrin π-delocalization in MgTFP compared to MgTThP and MgTPP. The differences in their structures are clearly reflected in their spectral and electrochemical properties. The absorption and fluorescence bands experienced bathochromic shifts on moving from six membered phenyls to five membered thienyl and furyl group, and the maximum effects were observed for meso-tetrafuryl Mg(Il) porphyrin. The electrochemical studies indicated that the gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) decreases as we move from six membered phenyl groups to five membered thienyl and furyl groups, which explains the bathochromic shifts observed in absorption and fluorescence bands. Results on Structure and electronic properties based on DFT studies are in agreement with experimental observations. [ABSTRACT FROM AUTHOR]

Click chemistry has been successfully applied in the synthesis of the first example of a triazole-bridged porphyrin dyad containing N2S2 porphyrin and N4 or ZnN4 porphyrin subunits, and fluorescence study indicated a possibility of singlet-singlet energy transfer from the N4 or ZnN4 porphyrin subunit to the N2S2 porphyrin subunit. [ABSTRACT FROM AUTHOR]

Synthesis of a series of 21-thia and 21-oxoporphyrin building blocks containing two pyridyl functional groups at the meso positions in a cis fashion is reported. The building blocks were used to synthesize a series of cationic water-soluble 21-thia and 21-oxoporphyrins. An unsymmetrical non-covalent trimer containing two dissimilar porphyrin cores such as one N3S and two N4 porphyrins cores was also constructed using the pyridyl porphyrin building blocks reported here. [Copyright &y& Elsevier]

The hexacoordinated rhenium(I) complex of 5,10,15,20-tetra-p-tolyl-21,23-dithiaporphyrin was synthesized, and the crystal structure analysis revealed the unusual binding mode of rhenium(I) to two thiophene sulfur atoms and one of the pyrrole nitrogen atoms of the porphyrin macrocycle. [ABSTRACT FROM AUTHOR]