N-Confused porphyrins: complexation and 1H NMR studies

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.

Photo-induced intramolecular electron transfer in phenoxazine-phthalocyanine donor-acceptor systems

Donor-Acceptor (D-A) systems based on phenoxazine – phthalocyanine (PXZ-Pc) and phenoxazine – zinc phthalocyanine (PXZ-ZnPc) have been designed and synthesized. Both D-A systems are characterized using various spectroscopic and electrochemical techniques including in-situ methods. Optical absorption studies suggest that both Soret and Q bands of these D-A systems are hypsochromically and bathochromically shifted, when compared to its individual constituents. The study supported by theoretical calculations shows clearly that there exists a negligible electronic communication in the ground state between donor phenoxazine and acceptor phthalocyanine. However, attractively, both D-A systems exhibit noteworthy fluorescence emission quenching (90–99%) of the phthalocyanine emission compared to its reference compounds. The fluorescence emission quenching featured at the excited-state intramolecular photoinduced electron transfer from ground state of phenoxazine to the excited state of phthalocyaine/zinc phthalocyanine. The rates of electron-transfer ([Formula: see text] of these D-A systems are found in the range of 5.7 × 108 to 2.8 × 109 s[Formula: see text] and are according to solvent polarity.

Photophysical study and in vitro approach against Leishmania panamensis of dicloro-5,10,15,20-tetrakis(4-bromophenyl)porphyrinato Sn(IV)

Background: Photodynamic therapy activity against different biological systems has been reported for porphyrins. Porphyrin modifications through peripheral groups and/or by metal insertion inside the ring are main alternatives for the improvement of its photo-physical properties. In this study, we synthesized and characterized 5,10,15,20-tetrakis(4-bromophenyl)porphyrin and the dicloro-5,10,15,20-tetrakis(4-bromophenyl)porphyrinato Sn(IV).

Methods: Metal-free porphyrin was synthesized using the Alder method, while the Sn(IV)-porphyrin complex was prepared by combining metal-free porphyrin with stannous chloride in DMF; the reaction yields were 47% and 64% respectively. Metal-free porphyrin was characterized by UV-Vis, FT-IR, ESI-mass spectrometry and ¹³C-NMR. Additionally, the Sn(IV) -porphyrin complex was characterized using UV-Vis and FT-IR. Cyclic voltammetry tests in four different solvents. The fluorescence quantum yield (Φ _f) was measured using fluorescein as a standard, the singlet oxygen quantum yield (Φ _D) was estimated using the standard 5,10,15,20-(tetraphenyl)porphyrin (H2TPP) and the quencher of singlet oxygen 1,3-diphenylisobenzofuran (DPBF).

Results: UV-Vis assay showed typical Q and Soret bands for porphyrin and its metallo-porphyrin complex. Compounds showed photoluminescence at the visible range of electromagnetic spectrum. The inclusion of the metal in the porphyrin core changed the Φ _f from 0.15 to 0.05 and the Φ _D increased from 0.55 to 0.59. Finally, the effect of the compounds on the viability of L. panamensis was evaluated by means of the MTT test. The results showed that both compounds decreased the viability of the parasite; this inhibitory activity was greater under light irradiation; the porphyrin compound had IC ₅₀ of 16.5 μM and the Sn(IV)-porphyrin complex had IC ₅₀ of 19.2 μM.

Conclusion: The compounds were synthesized efficiently, their characterization was carried out by different spectroscopy techniques and their own signals were evidenced for both structures, both compounds decreased the cell viability of L. panamensis.

Nucleophilic Aromatic Substitution (SNAr) and Related Reactions of Porphyrinoids: Mechanistic and Regiochemical Aspects

The nucleophilic substitution of aromatic moieties (SNAr) has been known for over 150 years and found wide use for the functionalization of (hetero)aromatic systems. Currently, several "types" of SNAr reactions have been established and notably the area of porphyrinoid macrocycles has seen many uses thereof. Herein, we detail the SNAr reactions of seven types of porphyrinoids with differing number and type of pyrrole units: subporphyrins, norcorroles, corroles, porphyrins, azuliporphyrins, N-confused porphyrins, and phthalocyanines. For each we analyze the substitution dependent upon: a) the type of nucleophile and b) the site of substitution (α, β, or meso). Along with this we evaluate this route as a synthetic strategy for the generation of unsymmetrical porphyrinoids. Distinct trends can be identified for each type of porphyrinoid discussed, regardless of nucleophile. The use of nucleophilic substitution on porphyrinoids is found to often be a cost-effective procedure with the ability to yield complex substituent patterns, which can be conducted in non-anhydrous solvents with easily accessible simple porphyrinoids.

High length-to-width aspect ratio lead bromide microwires via perovskite-induced local concentration gradient for X-ray detection

Well-oriented PbBr₂ microwires with a length-to-width ratio of up to 5000 were grown using a concentration gradient in co-crystallization with perovskite. Planar-integrated microwires showed a response to X-ray photons.

NH Tautomerism of N-Confused Porphyrin: Solvent/Substituent Effects and Isomerization Mechanism

The effects of substituents and solvents on the NH tautomerism of N-confused porphyrin (2) were investigated. The structures, electronic states, and aromaticity of NH tautomers (2-2H and 2-3H) were studied by absorption and nuclear magnetic resonance (¹H, ¹³C, and ¹⁵N) spectroscopies, single-crystal X-ray diffraction analysis, and theoretical calculations. The relative stability of the tautomers is highly affected by solvents, with the 3H-type tautomer being more stable in nonpolar solvents, while the 2H-type tautomer being highly stabilized in polar solvents with high donor numbers such as N,N-dimethylformamide (DMF), pyridine, and acetone. Electron-withdrawing groups on the meso-aryl substituents as well as the methyl group at the ortho position also stabilize the 2H-type tautomer. Kinetically, the tautomerism rate is significantly influenced by solvent and concentration, and a particularly large activation entropy (ΔS^⧧) is obtained in pyridine. The first-order deuterium isotope effect on the reaction rates of NH tautomerism (k_H/k_D) is determined to be 2.4 at 298 K. On the basis of kinetic data, the mechanism of isomerization is identified as an intramolecular process, including the rotation of the confused pyrrole in pyridine/chloroform and DMF/chloroform mixed solvent systems, and as a pyridine-mediated process in pyridine alone.