Peripheral Substituents Research Articles

Mass Spectrometry of Algal Chlorophyll c Compounds

Background: The term chlorophyll c encompasses a small but heterogeneous group of algal pigments, characterized for being porphyrins rather than chlorins. Chlorophylls c are protochlorophyllide-type compounds that differ in their peripheral substituents. Mass spectrometry has contributed to the structural elucidation of chlorophylls c, often in parallel with the development of soft ionization techniques. Objective: To provide comprehensive information on the structural characterization of chlorophylls c by mass spectrometry. Method: A detailed exam of the existing bibliography from both the chemical and marine science literatures followed by the analysis of data on molecular masses and product ions. Previous tandem mass spectra of chlorophyll c pigments are reproduced employing high resolution mass spectrometry. Results: This article reviews the application of direct and tandem mass spectrometry techniques to the analysis of acidic and esterified chlorophylls c, summarizes their fragmentation patterns and enumerates some experimental fragmentation rules for their identification. The high resolution mass spectra of acidic and esterified chlorophyll c compounds are shown as characteristic examples. Conclusion: The combined information on the molecular mass and diagnostic fragmentation allows the unambiguous characterization of the known acidic chlorophylls c, including the discrimination of isomeric pigments. Tandem mass spectrometry is a technique of choice for the study of galactolipid-esterified chlorophylls c, as the systematic fragmentation of successive parts in the molecules allows good tentative approaches to their structures. Keywords: Algae, chlorophylls c, chlorophyll c-galactoglyceride esters, fragmentation, mass spectrometry, protochlorophyllide, tandem mass spectrometry.

Influence of peripheral substituents on the stability of sandwich-type complexes of crown ether-containing anthraquinoneimines

ABSTRACTBenzo-15-crown-5 ether derivatives of 1-hydroxy-9,10-anthraquinone-9-imine bearing a substituted benzoylamino group, NHCO(p-C6H4NO2) or NHCOC6F5, in position 2 were synthesized by a photochemical method. The structure of the fluorine-containing compound was determined by single-crystal X-ray diffraction. Both synthesized dyes, as well as their analogue without substituents on the benzoyl ring, are capable of binding Sr2+ and Ba2+ to form sandwich-type 2:1 (ligand:metal) complexes. In MeCN, these complexes exhibit higher stability constants (K2:1) than the corresponding 1:1 complexes (K1:1). The para-substitution of the benzoyl ring with a nitro group leads to a significant increase in both the K2:1 constant and the K2:1/K1:1 ratio. The fluorination of the benzoyl ring insignificantly affects the stability of sandwich complexes. Density functional theory calculations showed that this is related to steric interactions in the benzoylamino group. The calculated structures of the dyes and their sandwich complexes with Ba2+ are consistent with the 2D NOESY data.

Silicon(IV) Corroles.

Silicon complexes of corrole were obtained for the first time by reaction of the free-base corrole with hexachlorodisilane. The peripheral substituents of corrole strongly influence the nature of the reaction products: β-octaalkyl corrole was mainly isolated as the μ-oxo dimer, while a hydroxo complex was obtained in the case of 5,10,15-tris-(pentafluorophenyl)corrole. In the case of meso-tritolyl corrole, a mixture of monomer/μ-oxo dimer was obtained. The silicon corrole complexes are more stable toward hydrolysis than the corresponding porphyrin derivatives and are endowed with brilliant luminescence properties. The high affinity of silicon for fluoride ion allowed investigation of the ability of an Si corrole to serve as a sensor for F- detection. The strong color variation due to the interaction with the halide ion makes the Si corrole an interesting material for the naked-eye detection of inorganic fluoride.

Synthesis, Structures, and Optical Properties of Azahelicene Derivatives and Unexpected Formation of Azahepta[8]circulenes.

Polycyclic heteroaromatic compounds including pyrrole units are promising functional scaffolds owing to their electron-rich nature, bright fluorescence, and applicability to anion recognition at the pyrrolic hydrogen atom. We report herein the effective synthesis of pseudo-aza[5]helicene and aza[7]helicene derivatives, and unexpected formation of azahepta[8]circulenes by oxidative fusion reactions. By choosing reaction conditions and peripheral substituents attached at the terminal indole moieties, we obtained aza[7]helicenes 10 a-c and azahepta[8]circulenes 11 a,c selectively in moderate to good yields. Their solid-state structures have been revealed by X-ray diffraction analysis. UV/Vis absorption, emission, and cyclic voltammetry of these compounds were studied in comparison with those of previously reported tetraaza[8]circulene (TA8C), a symmetric and planar molecule. Furthermore, the enantiomeric separation of dimethyl-substituted aza[7]helicene 10 b was achieved, and the racemization kinetics have been elucidated both theoretically and experimentally. This work illustrates a wealth of advantages of pyrrole incorporation into the polycyclic aromatic scaffolds in terms of synthetic aspects, structural variation, and optical tuning.

A Comprehensive Scope of Peripheral and Axial Substituent Effect on the Spectroelectrochemistry of Boron Subphthalocyanines.

An extensive study of the electrochemical and spectroelectrochemical properties of 14 boron subphthalocyanine (BsubPc) derivatives with various axial and peripheral substituents was performed in 1,2-dichloromethane (CH2Cl2) containing 0.1 M tetra- n-butyl-ammonium perchlorate (TBAP) as the supporting electrolyte. From the cyclic voltammetry results, all compounds exhibit one oxidation and at least two reduction processes within the solvent potential window of +1.6 to -1.8 V vs SCE. It was found that the reversibility of the redox reactions depends on the axial and peripheral substituents and the dipole moment of the boron-to-axial substituent. In general, UV-vis absorption spectra of the singly reduced BsubPc derivatives exhibit three equal intensity peaks in the 450 to 650 nm region that are derived from the maximum BsubPc absorbance peak upon reduction. Axial substituents affect the intensity of the three peaks upon reduction, while peripheral substituents shift the position of the peaks to higher wavelengths. Upon oxidation, the UV-vis absorption profile flattens considerably with only a single broad (∼300 nm) band apparent. Understanding the effect of substituents on the stability of the redox processes of BsubPcs will aid in further development of these materials for applications in organic electronic devices.

Design of Near-Infrared-Absorbing Unsymmetrical Polymethine Dyes with Large Quadratic Hyperpolarizabilities

Fifteen heptamethine dyes in which a tricyanofuran acceptor is linked to donors of different strengths were synthesized, and their absorption, thermal, electrochemical, and second-order nonlinear optical properties were investigated. While the variation of the peripheral bulky substituents allowed a decrease of the intermolecular interactions in the solid state, subtle engineering of the heterocyclic donor provided dyes with electronic structures that varied between dipolar and cyanine-like (i.e., with little bond length alternation and with ground and excited states having similar dipole moment) and remarkably high quadratic hyperpolarizabilities (μβ1.9) of up to 115 000 × 10–48 esu.

Supramolecular Chemistry of Cobalt-Corrins

Cobalt corrins are chiral relatives of the cobalt porphyrins, in which the ligand is much less unsaturated and is also ‘contracted’ by one carbon. This type of ligand strongly affects the redox and coordination chemistry of the bound cobalt center. Some lipophilic artificial cobalt corrins have been prepared in tremendous synthetic efforts in the Eschenmoser labs. The natural analogues offer an apparently more straight forward chemical entry to cobalt corrins. However, the natural cobalt corrins are all hydrophilic and highly substituted at their periphery, and they are distantly related to heme and chlorophyll. Although these cobalt corrins are very soluble in water, their natural roles are intimately connected with their essential and rich organometallic chemistry, which is all cobalt-centered.[1] In this lecture, means for specific supramolecular assemblies based on modified natural cobalt corrins are delineated, as well as consequences of the supramolecular restructuring on the organometallic and redox-chemistry. So far, in the excursions to be reported, the cobalt corrin core is not altered and its redox and spectral properties are largely conserved. A unique basis for specific supramolecular assemblies is then provided by the (organometallic) ligand itself, either, when attached to and bridging more than one metal center, or, when providing a structuring interface itself, for the build-up of supra-molecules. In a second general type of supramolecular assemblies the functional groups attached at the peripheral substituents of the natural corrinoids are used in a uniform way. By this means, the direct environment of the cobalt corrin moiety may be affected and structured in a global fashion, generating, e.g., a type of molecular micelles. A third type of supramolecular assembly makes selective use of single sites of the complex, but largely conserved sphere of the peripheral substituents, in order to generate specifically structured cobalt-corrins and their dimers. These latter ones may feature binuclear (organometallic) coordination chemistry, which would allow for synchronized redox processes in a highly structured, ‘second’ sphere around the metal centers. I thank the Austrian Science Foundation (FWF, project P-28892 and earlier projects) for generous financial support.

Ion-Pairing Assemblies and Materials Comprising Charged Porphyrins

π-Electronic ions with appropriate geometries and peripheral substituents would provide assemblies through interactions between building subunits, resulting in fascinating electronic properties. Diverse ion-responsive π-electronic systems and π-electronic ions were prepared, affording dimension-controlled ion-pairing assemblies as crystals, supramolecular gels, and thermotropic liquid crystals (LCs).[1] Structures and properties of the assemblies can be controlled by the combined negatively and positively charged species in the assemblies. Highly ordered arrangement of charged species, not only the ion complexes but also charged π-systems, has been found to be a key factor to exhibit the enhanced performance as fascinating electronic materials.[2] Recently, ion pairs based on porphyrin-AuIII complexes as π-electronic cations were prepared with the combination of various anions including a π-electronic anion. Porphyrin-AuIII complexes possessing aliphatic alkyl chains formed dimension-controlled ion-pairing assemblies as thermotropic liquid crystals, whose ionic components were highly organized by electrostatic and π–π stacking interactions.[3,4] References A recent review: Haketa, Y.; Maeda, H. Chem. Commun. 2017, 53, 2895.As an example of an anionic porphyrin: Sasano, Y.; Yasuda, N.; Maeda, H. Dalton Trans. 2017, 46, 8924.Haketa, H.; Bando, Y.; Yasuda, N.; Hisaki, I.; Maeda, H. to be submitted.Sasano, Y.; Yasuda, N.; Maeda, H. to be submitted.

Novel Corroles for Chemical Sensor Applications

In the last few years corrole has been one of the protagonist of the porphyrinoid scenario, due to the impressive number of researches devoted to investigate the chemistry of such a macrocycle. The refinement of simple synthetic routes for the preparation of meso-substituted corroles made this macrocycle easily available to researchers, before hampered by the multi-step preparation necessary to obtain this contracted porphyrin. Although this synthetic availability contributed to the corrole popularity, it is for sure the peculiarity of the chemistry of such a macrocycle that justified the impressive increase in researches related to corroles. This peculiarity is characterized by the non-innocent character as ligand, which from one side makes its behavior particularly intriguing and challenging for the electronic structure characterization, and from the other side makes its metal derivatives interesting for catalytic applications. To further enrich this scenario, it is important to study different synthetic routes devoted to the modification of the corrole ring, by the introduction of peripheral substituents. In this way it is possible to modulate the characteristics of the corrole ligand and consequently its metal derivatives. In the present work we summarize our recent achievements in the preparation of novel corrole derivatives for chemical sensors development.

Subnaphthalocyanines as Electron Acceptors in Polymer Solar Cells: Improving Device Performance by Modifying Peripheral and Axial Substituents.

A new class of subnaphthalocyanines bearing various peripheral and axial substituents have been synthesized for use as electron acceptors in solution‐processed bulk‐heterojunction polymer solar cells. The resulting solar cells exhibit modest photovoltaic performance with contributions from both the polymer donor and subnaphthalocyanine acceptor to the photocurrent.

Raman spectra study of p-tert-butylphenoxy-substituted phthalocyanines with different central metal and substitution positions

Metallophthalocyanine (MPc) derivatives show excellent photoelectric and magnetic properties due to their large π-conjugate system. Central metals and peripheral substituents are two important ways to adjust and optimize the properties of MPc via tuning the large π-conjugate system. In this work, Raman scattering spectra of MPc, including ZnPc, CuPc, CoPc, and NiPc, were investigated. The most intense band in the Raman spectra at about 1500 cm−1, owing to the vibration of CNC bridge bonds, shifts significantly with the size of the metal ion, indicating a good marker of metal ion effect on the changes of the Raman shift. For the MPc with suitable sizes of metal ions (e.g., Zn2+, Cu2+, Co2+, Ni2+), the structure of phthalocyanine ring is planar. The ring will be distorted according to the different forces of the central metal ions. When the polarization force of the central metal ion enhances (Zn2+ < Cu2+ < Co2+ < Ni2+), the Raman shift of CNC would simultaneously increase, and the bigger polarization force could lead to a larger Raman shift (ZnPc < CuPc < CoPc < NiPc). On the other hand, the CNC Raman shift of the 3-substituted MPc was relatively smaller than that of the 4-substituted one with the same central metal ion. When the electron density of the phthalocyanine ring was relatively low, the energy of the system would increase and the Raman peak would correspondingly shift distinctly. Our Raman spectra results are consistent with the UV–vis measurement results. This work will provide the basis for structure analysis, and design of new molecular materials, as well as their application.

The chitosan – Porphyrazine hybrid materials and their photochemical properties

Three magnesium sulfanyl porphyrazines differing in the size of peripheral substituents (3,5-dimethoxybenzylsulfanyl, (3,5-dimethoxybenzyloxy)benzylsulfanyl, 3,5-bis[(3,5-bis[(3,5-dimethoxybenzyloxy)benzyloxy]benzylsulfanyl) were exposed to visible and ultraviolet radiation (UV A + B + C) in order to determine their photochemical properties. The course of photochemical reactions in dimethylformamide solutions and the ability of the systems to generate singlet oxygen were studied by UV–Vis spectroscopy, which additionally gave information on aggregation processes. The porphyrazines were found to be stable upon visible light irradiation conditions, but when exposed to high energy UV radiation, the efficient photodegradation of these macrocycles was observed. Therefore, these three magnesium sulfanyl porphyrazines were incorporated into chitosan matrix. The obtained thin films of chitosan doped with porphyrazines were subjected to polychromatic UV-radiation and studied by spectroscopic methods (UV–Vis, FTIR), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Application of chitosan as a polymer matrix for porphyrazines was found to be successful method that effectively stopped the unwelcome degradation of macrocycles, thus worth considering for their photoprotection. In addition, the surface properties of the hybrid material were determined by contact angle measurements and calculation of surface free energy. Intermolecular interactions between these novel porphyrazines and chitosan were detected. The mechanism of photochemical reactions occurring in studied systems has been discussed.

Exploration of Hypervalent Lewis Acid/Base Interactions in 2-(2'-Thiazolyl)-3-thienylphosphanes.

The synthesis of a series of conjugated organophosphorus materials with intramolecular Lewis acid/base interactions and the exploration of the electronic nature of the bonding around the resulting hypervalent phosphorus centers are reported. To further establish the influence of increasing the size of the π-conjugated backbone, two scaffolds, thiazolyl-thiophene and benzothiazolyl-thiophene, were included in this study. Single-crystal X-ray crystallography of several of the compounds supports the hypervalent nature of the phosphorus center in the new species. Surprisingly, altering the Lewis acidity of the phosphorus center via oxidation or methylation impacts the coordinating mode of the thiazolyl substituent, which also has considerable impact on the photophysical and electrochemical properties of the π-conjugated molecular scaffolds. Through theoretical calculations involving natural bond orbital (NBO) analysis and atom-in-molecules (AIM) correlation, the existence and electronic nature of weak hypervalent bonding interactions around the phosphorus center was solidified as weak 3c-4e and/or σ-hole bonds, depending on the coordination mode of the peripheral thiazolyl substituent as well as the Lewis acidity of the phosphorus center.

Effect of central metals and peripheral substituents on the third-order nonlinear optical properties of tetra-benzimidazole and benzothiazole substituted phthalocyanines

A series of tetra substituted phthalocyanines bearing 2-mercaptobenzimidazole or 2-mercaptobenzothiazole units with different central metals (Zn and In) were synthesized. Their photophysical properties including the parameters of fluorescence and triplet state were studied. The benzothiazole substituted phthalocyanines exhibit stronger third-order nonlinear optical properties (NLO) absorption effects, higher triplet quantum yield (ΦT) and faster intersystem crossing rate compared to the benzimidazole substituted phthalocyanines. With the same central metals, benzothiazole substituted phthalocyanine complexes have the lower fluorescence quantum yield (ΦF), the higher triplet quantum yield (ΦT) and the larger third-order NLO properties as a result of larger conjugated structure and spin-orbit coupling induced by sulphur atoms. The influences of the central metal atoms and the peripheral substituents on the third-order NLO properties are discussed using photophysical parameters.

Photophysical properties of free-base and manganese(iii) N-confused porphyrins.

The photophysical properties of N-confused 5,10,15,20-tetraphenyl porphyrin derivatives have been studied using steady-state and time-resolved spectroscopic techniques. The peripherally substituted N-confused 5,10,15,20-tetraphenyl free-base porphyrins (NCTPPs) show stronger B-band absorptions in DCM than in DMAc, while much stronger emissions have been observed in DMAc, which may be due to the shorter times (τIC) of internal conversion from the B-band to the Q-band. The Q-band spectral structures of NCTPPs in DCM are significantly different from those in DMAc. The introduction of ortho-OCH3 results in the strongest emission in both DCM and DMAc and significant fluorescence after N-methylation even though the emissions of other N-methyl complexes are quenched. The N-methylation of NCTPPs leads to a larger τIC and shorter emission lifetime. The excited-state dynamics of manganese(iii) N-confused porphyrins (Mn(Cl)NCH3NCTPPs) are influenced by both peripheral substituents and manganese(iii) metal ion, and exhibit ultrafast intersystem crossing processes.

Synthesis of Water-Soluble Phthalocyanines and Modification of their Peripheral Fragments as a Method of Directed Changes in Lipophilic-Hydrophilic Properties

This article brief by describes results of studies devoted to synthesis of water-soluble phthalocyanines derivatives, which are carried out by the Complexing Agents Chemistry group of IPAC RAS. Metal-free ligands and metallophthalocyanines, containing peripheral substituents with fragments of pyridine, oxybenzoic and hydroxyphenylphosphonic acids are potential photosensitizers for photodynamic therapy of cancer diseases. Methods for the modification of peripheral substituents have been developed that make it possible to synthesize phthalocyanine ligands and complexes soluble in organic solvents, or soluble in aqueous media and also possess amphiphilic properties.

Distribution of the unpaired electron in neutral bis(phthalocyaninato) yttrium double-deckers: An experimental and theoretical combinative investigation

The location of the unpaired electron in neutral bis(phthalocyaninato) yttrium double-decker complexes, with different substituents, has been studied on the basis of both experimental methods and density functional theory (DFT) calculations over the molecular structures, atomic charges, electronic absorption, infrared spectra, and electron paramagnetic resonance. The results reveal the location of the unpaired electron mainly on the carbon atoms of both tetrapyrrole chromophores with the population distribution obviously affected by the peripheral substituents.

Fluorescent Rosamine/TiO2 Composite Films for the Optical Detection of NO2

Two rosamine derivatives were used as fluorescent sensors for the detection of NO2, a toxic and oxidant gas whose presence in populated areas needs to be controlled. Both compounds shared the same molecular structure but had different peripheral substituents: a carboxylic acid and an amino group. Transparent nanocrystalline TiO2 films were prepared by screen printing and used as substrates, where the rosamines were incorporated by simple immersion into their respective solutions to form composite films. According to the molecular structures of the rosamines, the anchoring to the substrates was proposed to be by either covalent bonding and electrostatic interaction, or only electrostatic interaction, and was determined by the different substituents in each rosamine. Upon their exposure to increasing concentrations of NO2, both types of composite films showed intense and fast spectral changes, and the speed of response was related to the concentration of the gas. The anchoring mode and the electrophilic effect of the substituents determined the better sensing capability and the faster response shown by the carboxylic derivative in all cases.

Pyridone substituted phthalocyanines: Photophysico-chemical properties and TD-DFT calculations

4-(6-methyl-3-nitro-2-oxo-1,2-dihydropyridin-4-yloxy)phthalonitrile has been used to prepare a novel Zn(II) phthalocyanines with four peripheral pyridone substituents. The compound has been characterized by UV-visible absorption, FT-IR and [Formula: see text]H-NMR spectroscopy, elemental analysis and MALDI-TOF mass spectroscopy. The fluorescence, triplet quantum and singlet oxygen quantum yields have been determined and TD-DFT calculations have been used to identify trends in the electronic structure.

Radiative Deactivation of Lowest Singlet and Triplet Excited States of Water-Soluble Porphyrins

Radiative deactivation of lowest excited triplet and singlet states for series of free bases and Zn2+-complexes of water-soluble 5,10,15,20-tetrakis-(4-sulfonatophenyl)porphyrin (H2T4SPP); 5,10,15,20-tetrakis-(4-N-alkylpyridyl) porphyrin (H2T4AlkPyP); and 5,10,15,20-tetrakis-(3-N-alkylpyridyl)porphyrin (H2T3AlkPyP) was studied in solutions at 77 and 293 K. The fluorescence and phosphorescence quantum yields were found to have small but detectable differences for derivatives of the same porphyrin ligand with different counterions for the ionized aryl substituents. It was shown that these differences were due to spin–orbit coupling effects and variation of the electron donor/acceptor properties of the peripheral substituents that changed the electronic energy levels in the porphyrin–counterion system.