Novel expanded porphyrinoids with multiple-inner-ring-fusion and/or tunable aromaticity

A Class of Heptaphyrins with NIR Absorption Modulated by Metal Coordination and Nucleophilic Substitution

The intensive interest in expanded porphyrins can be attributed to their appealing photoelectric and coordination behavior. In this work, an N-confused heptaphyrin 1 was synthesized by an acid-catalyzed [3+4] condensation reaction. The introduction of an N-confused pyrrolic unit into the heptaphyrin macrocycle led to the formation of a figure-eight-like conformation with nonsymmetrical "NNNN" and "NNNC" coordination cavities employable for bimetallic coordination. As a result, chelation of 1 with Zn(II) and Cu(II) afforded mono-Zn(II) complex 2 and bis-Cu(II) complex 3, respectively, with the metal atoms exhibiting distorted square-planar geometries. In complex 3, an oxygen atom is attached to the α-C atom of N-confused pyrrole D, and thus the N and C atoms of ring D participate in coordination within the two cavities. Interestingly, treatment of 1 with Cs2CO3 in MeOH resulted in regioselective substitution of all the seven para-F atoms in the meso-C6F5 groups as well as the α-H of ring D by eight methoxy moieties. Complex 3 displays a red-shifted absorption band edge of ca. 2200 nm, compared to that of ca. 1600 nm observed for 1. This work provides an example of incorporating an N-confused pyrrole to construct expanded porphyrins with distinctive coordination behavior and tunable NIR absorption.

Heptagon/Octagon-Fused Diporphyrins or Spiro-Pentagon-Bridged Dichlorin from p-Terphenylene-Bridged Diporphyrin

Intramolecular fusion reactions of a p-terphenylene-bridged Ni^II porphyrin dimer gave different products, depending upon reaction conditions. Oxidation with Fe(OTf)₃ provided syn- and anti-doubly heptagon-fused Ni^II porphyrin dimers showing enlarged π-electronic networks, probably via a radical mechanism, while treatment with methanesulfonic acid provided a spiro-pentagon-bridged Ni^II chlorin dimer via acid-catalyzed Friedel-Crafts type cyclization. Further, a doubly octagon-fused Ni^II porphyrin dimer was synthesized via a sequence of double meso-formylation, reduction to corresponding diol, and BF₃ -catalyzed cyclization.

Methyl 12-Methyl-3,9-dinitro-5,6,7,12-tetrahydro-13-oxodibenzo[b.g]bicyclo[3.3.1]nonane-6-carboxylate and Related Compounds

A synthesis of the title compound and related structures is reported. The procedure involves double alkylation of a β-ketoester followed by double SNAr ring closure from the γ carbon to give a dibenzo[3.3.1]bicyclic unit. This paper appears to be the first to generate a mid-sized bicyclic target by a double SNAr process. The synthesis can be performed in one step, but yields are superior (52–62%) when a two-stage procedure is used.

Doubly Fused Unsymmetrical Calixdicarbahexaphyrins

Three novel doubly fused unsymmetrical calixdicarbahexaphyrins were synthesized by mild acid-catalyzed (4+2) condensation of dicarbatetrapyrrane with dipyrroethene diol followed by oxidation. The condensation formed doubly fused calixdicarbahexaphyrins instead of π-conjugated dicarbahexaphyrins, due to the unusual fusion of the pyrrole N with the α-carbon of the adjacent pyrrole ring to form a tripentacyclic ring and one usual fusion of the pyrrole N with the adjacent phenylene C to form a fused moiety containing two pentacycles and one hexacycle ring. Both fusions occurred on one side of the macrocycle, making the macrocycles unsymmetric. The crystal structure obtained for one of the macrocycles exhibited a saddle-shaped structure with two benzene rings and four pyrrole rings connected via two ethylene and four methene meso-carbon atoms. The crystal structure also revealed unusual fusions in the macrocyclic framework and the presence of one sp³ carbon that disrupts the π-electron delocalization. ¹H, ¹H-¹H COSY, NOESY, ¹³C, and HMBC NMR techniques were used to characterize the macrocycles. The absorption spectra of the macrocycles showed one intense sharp band at ∼485 nm along with a shoulder in the lower-energy region, suggesting its non-aromatic nature. Electrochemical studies indicated their electron rich nature, and DFT/TD-DFT studies corroborated the experimental observations.

Creation from Confusion and Fusion in the Porphyrin World─The Last Three Decades of N-Confused Porphyrinoid Chemistry

Confusion is a novel concept of isomerism in porphyrin chemistry, delivering a steady stream of new chemistry since the discovery of N-confused porphyrin, a porphyrin mutant, in 1994. These days, the number of confused porphyrinoids is increasing, and confusion and associated fusion are found in various fields such as supramolecular chemistry, materials chemistry, biological chemistry, and catalysts. In this review, the birth and growth of confused porphyrinoids in the last three decades are described.

Doubly N-confused phlorin and phlorinone analogue

A doubly N-confused phlorin and phlorinone analogue were synthesized from a β,β'-linked dipyrromethane precursor and characterized by means of NMR and UV-Vis spectroscopies, X-ray crystallography, and electrochemistry. Solvents have a considerable impact on the optical absorption of the doubly N-confused phlorin so that it can differentiate simple alcohols such as methanol and ethanol.

Porphyrin metalation catalyzed by DNAzymes and nanozymes

In this review, DNA and nanomaterial based catalysts for porphyrin metalation reactions are summarized, including the selection of DNAzymes, choice of nanomaterials, their catalytic mechanisms, and applications of the reactions.

Light-Absorbing Pyridine Derivative as a New Electrolyte Additive for Developing Efficient Porphyrin Dye-Sensitized Solar Cells

To fabricate efficient dye-sensitized solar cells (DSSCs), 4-tert-butylpyridine (TBP) is commonly used as an additive in the electrolytes for improving the photovoltages (V_OC). However, TBP cannot play a positive role in improving the photocurrent (J_SC) because of the lack of absorption in the visible-wavelength range. We herein report a light-absorbing pyridine derivative N1 as an additive for the axial coordination with porphyrin dyes. N1 was synthesized by introducing a (bis(4-methoxyphenyl)amino)anthryl moiety into the para-position of pyridine via an acetylene bridge, and porphyrin dye XW64 containing meso-3,5-disubstituted phenyl groups was synthesized considering that the meta-substituted phenyl groups may induce weaker steric hindrance with the axial pyridyl ligand, as compared with wrapped and strapped porphyrin dyes. Thus, N1 was used as an electrolyte additive together with TBP. When optimized concentrations of 6 mM N1 and 0.5 M TBP were used for fabricating DSSCs based on XW64, enhanced photovoltaic performance was achieved, with J_SC, V_OC, and efficiency of 15.65 mA·cm^-2, 0.701 V, and 7.35%, respectively, superior to those of the corresponding DSSCs without using the additives (J_SC = 14.86 mA·cm^-2, V_OC = 0.599 V, and efficiency = 5.94%). The enhancement of J_SC can be ascribed to the improved light-harvesting ability induced by the axially coordinated N1. Furthermore, the two additives also can be used to fabricate efficient solar cells based on the wrapped porphyrin dye XW42, achieving high efficiency of 10.3%, indicative of their general applicability in fabricating high-performance DSSCs. These results indicate that the simultaneous employment of the traditional TBP additive and a pyridyl ligand with light-harvesting ability in the electrolyte for the axial coordination to a porphyrin dye is a promising approach for developing efficient DSSCs.

Rational Synthesis of 5,5,5-Tricyclic Fused Thia-heptaphyrin (1.1.1.1.1.1.0) From a Helical Oligopyrrin Hybrid

Oxidation of a thiophene-hexapyrrane hybrid S-P₆ afforded a stable conjugated open-chain thiaheptapyrrolic helix 1 with the terminal thiophene and confused pyrrole units lying at a long distance that is adverse for further cyclization. Chelation of 1 with copper(II) ion afforded 1-Cu, which exhibits more distant terminal units. Interestingly, further oxidation of 1 triggered an intramolecular C-N fusion reaction to afford a unique 5,5,5-tricyclic fused linear thiaheptapyrrin 2, with the two terminals positioned in proximity, which favors the oxidative ring-closure reaction to give a unique 5,5,5-tricyclic fused thiaheptaphyrin (1.1.1.1.1.1.0) 3 under air. The inner-fusion strategy for positioning the reactive sites in proximity to promote oxidative cyclization offers a new approach for constructing large porphyrinoids through conjugated oligopyrrins without the assistance of metal ions.

Tripyrrin-armed isosmaragdyrins: synthesis, heterodinuclear coordination, and protonation-triggered helical inversion

Oxidative ring closure of linear oligopyrroles is one of the synthetic approaches to novel porphyrinoids with dinuclear coordination sites and helical chirality. The spatial arrangement of the pyrrolic groups of octapyrrole (P8) affected the position of the intramolecular oxidative coupling of the pyrrolic units; tripyrrin-armed isosmaragdyrin analogue (1) containing a β,β-linked bipyrrole moiety was synthesized regioselectively in a high yield by using FeCl₃. Ni^II-coordination at the armed tripyrrin site of 1 allowed the formation of diastereomeric helical twisted complexes (2A and 2B) and succeeding Cu^II-coordination at the macrocyclic core afforded heterodinuclear Ni^II/Cu^II-complexes (3A and 3B). Each of them comprised a pair of separable enantiomers, exhibiting P- and M-helices, respectively. Notably, diastereomeric interconversion from 2A to 2B was quantitatively achieved as a consequence of helical transformation under acidic conditions.

Near-IR absorbing J-aggregates of a phenanthrene-fused BODIPY as a highly efficient photothermal nanoagent

A phenanthrene-[b]-fused BODIPY exhibited well-defined J-aggregates in both pure hydrocarbon solution and aqueous solution, and was developed as a highly efficient photothermal nanoagent.