2,3,12,13‐Tetrabromo‐5,10,15,20‐tetrakis(4‐butoxyphenyl)porphyrin 1,2‐dichloroethane solvate

Nonmesogenic 2,3,12,13‐tetrabromo‐5,10,15,20‐tetrakis(4‐butoxyphenyl)porphyrin crystallizes as the title 1,2‐dichloroethane solvate, C₆₀H₅₈Br₄N₄O₄·C₂H₄Cl₂. The porphyrin ring shows a nonplanar conformation, with an average mean plane displacement of the β‐pyrrole C atoms from the 24‐atom (C₂₀N₄) core of ±0.50 (3) Å. The 1,2‐dichloroethane solvent is incorporated between the porphyrin units and induces the formation of one‐dimensional chains via interhalogen Cl...Br and butyl–aryl C—H...π interactions. These chains are oriented along the unit‐cell a axis, with the macrocyclic ring planes lying almost parallel to the (010) plane. The chains are arranged in an offset fashion by aligning the butoxy chains approximately above or below the faces of the adjacent porphyrin core, resulting in decreased interporphyrin π–π interactions, and they are held together by weak intermolecular (C—Br...π, C—H...π and C—H...Br) interactions. The nonplanar geometry of the macrocyclic ring is probably due to the weak interporphyrin interactions induced by the solvent molecule and the peripheral butoxy groups. The nonplanarity of the mesogens could influence the mesogenic behaviour differently relative to planar porphyrin mesogens.     

Spectrophotometric determination of tellurium(IV) in environmental and telluride film samples

Three simple, rapid, and sensitive spectrophotometric methods for the determination of traces and ultratraces of tellurium(IV) were studied. These methods were based on either the oxidation of 4-bromophenylhydrazine (4-BPH) by tellurium in a basic medium and coupling with N-(1-naphthyl)ethylenediamine dihydrochloride (NEDA) to give a purple-colored product, the oxidation of 3-methyl-2-benzothazoline hydrazone hydrochloride (MBTH) by tellurium in a basic medium and coupling with chromotropic acid (CA) to yield a red-colored species, or the oxidation of 2,3-dimethoxystrychnidin-10-one (2,3-DMSO) by tellurium in an acidic medium to yield an orange-colored derivative. Beer’s law was obeyed in the range 1.0–25 μg/mL (purple-colored product), 0.7–20 μg/mL (red-colored species), and 0.3–15 μg/mL (orange-colored derivative). The reaction conditions and other analytical parameters were investigated to enhance the sensitivity of the proposed methods. The tolerance limit of various ions has been studied. The methods were applied to the analysis of tellurium in water samples (waste, river, lake, and spring), plant materials, soil samples, and telluride thin films. The results obtained were superior to those obtained using the reported method. The performances of the proposed methods were evaluated in terms of ‘t’-test and variance ratio ‘f’-test, which indicate the advances of the proposed methods over reported methods. The text was submitted by the authors in English.     

Covalently linked bisporphyrins bearing tetraphenylporphyrin and perbromoporphyrin units: Synthesis and their properties

A series of covalently linked bisporphyrins bearingmeso-tetraphenylporphyrin (TPP) and octabromotetraphenylporphyrin (OBTPP) units have been synthesised and characterised. Electrochemical studies on these bisporphyrins showed an anodic shift (∼ 30–60 mV) of the TPP unit and a cathodic shift (∼40-80 mV) of OBTPP in redox potentials. Further, steady-state fluorescence studies on bisporphyrins indicated dramatic decrease in fluorescence quantum yields of the TPP moiety. Electrochemical redox and fluorescence data seem to suggest the possible existence of intramolecular interactions in these bisporphyrins     

An improved protocol for the synthesis of antipodal β-tetrabromo-tetraphenylporphyrin and the crystal structure of its Zn(II) complex

This work reports an improved protocol for the regioselective synthesis of 2,3,12,13-tetrabromo-5,10,15,20-tetraphenylporphyrin (H₂TPPBr₄) and the crystal structure of its Zn(II) complex which shows saddle shaped geometry.     

meso -Tetrathienylporphyrins: Steady-state emission and structural properties

meso-Tetra (2′- and 3′-thienyl)porphyrins and their Zn(II)-complexes were examined by steady-state fluorescence measurements. These molecules exhibit significant bathochromic shift in their emission bands with decreased quantum yields relative to their correspondingmeso-tetraphenylporphyrin derivatives. The crystal structure of 5,10,15,20-tetrakis(3′-thienyl)porphinato zinc(II) shows planar and nonplanar stereochemical features of the macrocycle. One of the macrocycle shows nearly planar while the other exhibited predominantly saddle-shaped geometry. The extent of displacement of the Β-pyrrole carbons in the nonplanar (saddle) conformation is as high as ± 0·422 ?.     

[5,10,15,20-Tetrakis(2-thienyl)porphyrinato]zinc(II)

In the title complex, [Zn(C₃₆H₂₀N₄S₄)], the Zn^II ion occupies a special position on an inversion centre with four-coordinate geometry. The porphyrin ring shows a wave-like conformation, with the closest interporphyrin plane separation being 3.60 (6) Å. The two disordered thienyl groups are inclined with respect to the porphyrin plane at angles of 70 (4) and 67 (2)°.     

Supramolecular chirogenesis in bis-porphyrins: interaction with chiral acids and application for the absolute configuration assignment

[structure: see text] A new supramolecular chirogenic system on the basis of bis(free base porphyrin) and various enantiopure acids, which can be effectively applied for the chirality sensing purposes, is reported. The temperature and solvent are found to be key factors controlling the chirality transfer process in these assemblies.     

Planar and Nonplanar Free‐Base Tetraarylporphyrins: β‐Pyrrole Substituents and Geometric Effects on Electrochemistry,Spectroelectrochemistry, and Protonation/Deprotonation Reactions in Nonaqueous Media

A series of planar and nonplanar free‐base β‐pyrrole substituted meso‐tetraarylporphyrins were characterized by electrochemistry, spectroelectrochemistry, and protonation or deprotonation reactions in neutral, acidic, and basic solutions of CH₂Cl₂. The neutral compounds are represented as H₂(P), in which P represents a porphyrin dianion with one of several different sets of electron‐withdrawing or ‐donating substituents at the messo and/or β‐pyrrole positions of the macrocycle. The conversion of H₂(P) to [H₄(P)]²⁺ in CH₂Cl₂ was accomplished by titration of the neutral porphyrin with trifluoroacetic acid (TFA) while the progress of the protonation was monitored by UV/Vis spectroscopy, which was also used to calculate logβ₂ for proton addition to the core nitrogen atoms of the macrocycle. Cyclic voltammetry was performed after each addition of TFA or TBAOH to CH₂Cl₂ solutions of the porphyrin and half‐wave potentials for reduction were evaluated as a function of the added acid or base concentration. Thin‐layer spectroelectrochemistry was used to obtain UV/Vis spectra of the neutral and protonated or deprotonated porphyrins under the application of an applied reducing potential. The magnitude of the protonation constants, the positions of λ_max in the UV/Vis spectra and the half‐wave or peak potentials for reduction are then related to the electronic properties of the porphyrin and the data evaluated as a function of the planarity or nonplanarity of the porphyrin macrocycle. Surprisingly, the electroreduction of the diprotonated nonplanar porphyrins in acid media leads to H₂(P), whereas the nonplanar H₂(P) derivatives are reduced to [(P)]^2? in CH₂Cl₂ containing 0.1 M tetra‐n‐butylammonium perchlorate (TBAP). Thus, in both cases an electrochemically initiated deprotonation is observed.     

Mixed substituted porphyrins: structural and electrochemical redox properties

To examine the influence of mixed substituents on the structural, electrochemical redox behavior of porphyrins, two new classes of beta-pyrrole mixed substituted free-base tetraphenylporphyrins H2(TPP(Ph)4X4) (X = CH3, H, Br, Cl, CN) and H2(TPP(CH3)4X4) (X = H, Ph, Br, CN) and their metal (M = Ni(II), Cu(II), and Zn(II)) complexes have been synthesized effectively using the modified Suzuki cross-coupling reactions. Optical absorption spectra of these porphyrins showed significant red-shift with the variation of X in H2(TPPR4X4), and they induce a 20-30 nm shift in the B band and a 25-100 nm shift in the longest wavelength band [Q(x)(0,0)] relative to the corresponding H2TPPR4 (R = CH3, Ph) derivatives. Crystal structure of a highly sterically crowded Cu(TPP(Ph)4(CH3)4).2CHCl3 complex shows a combination of ruffling and saddling of the porphyrin core while the Zn(TPP(Ph)4Br4(CH3OH)).CH3OH structure exhibits predominantly saddling of the macrocycle. Further, the six-coordinated Ni(TPP(Ph)4(CN)4(Py)2).2(Py) structure shows nearly planar geometry of the porphyrin ring with the expansion of the core. Electrochemical redox behavior of the MTPPR4X4 compounds exhibit dramatic cathodic shift in first ring oxidation potentials (300-500 mV) while the reduction potentials are marginally cathodic in contrast to their corresponding MTPPX4 (X = Br, CN) derivatives. The redox potentials were analyzed using Hammett plots, and the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap decreases with an increase in the Hammett parameter of the substituents. Electronic absorption spectral bands of H2TPPR4X4 are unique that their energy lies intermediate to their corresponding data for the H2(TPPX8) (X = CH3, Ph, Br, Cl) derivatives. The dramatic variation in redox potentials and large red-shift in the absorption bands in mixed substituted porphyrins have been explained on the basis of the nonplanarity of the macrocycle and substituent effects.