Journal of Porphyrins and Phthalocyanines

This review provides examples illustrating the powerful combination of resonance Raman spectroscopy and site-directed mutagenesis to investigate the structure-function relationship in structurally different heme proteins with diverse physiological functionality. The selective mutation of key amino acid residues gives rise to distinct spectroscopic fingerprints, as a result of the subtle alterations of the heme pocket environment. This review includes, but it is not limited to, the study of: i) the interactions between bound exogenous ligands with distal residues, ii) the effects of hydrogen bonds between the proximal residues and the surrounding cavity, iii) the interaction between the peripheral substituents of the heme group with the protein matrix with the concomitant effect on specific biological processes.

Tetrapyrazinoporphyrazines (TPyzPzs) likely represent the most investigated group of azaanalogs of phthalocyanines. This review highlights the author’s contributions in this field and summarizes the most important features of these interesting macrocycles with the aim of emphasizing the differences from the parent phthalocyanines. In particular, uniqueness in synthesis, spectral, photophysical and electrochemical properties are discussed. Thanks to systematic investigation of intramolecular charge transfer with TPyzPzs as electron acceptors, detailed structure-activity relationships of this ultrafast quenching process have been disclosed. This opened the door for the use of TPyzPzs as fluorescence sensors and quenchers in oligodeoxynucleotide probes, the latter being unique for TPyzPzs, which have not been investigated with phthalocyanines. These two applications seem to be much more suitable for TPyzPzs than photodynamic therapy, where the phthalocyanines typically have superior in vitro activities.

Due to their strong acceptor properties and enhanced charge transport capabilities, non-fullerene electron acceptors based on $\pi$-extended derivatives – subnaphthalocyanines (SubNc) or subphtalocyanine dimers (SubPc${}_2)$ – have been employed in organic photovoltaics in the past as an alternative to the expensive fullerene. However, these promising $\pi$-extended derivatives have not been explored in perovskite solar cell technology. In this work, we implement a vacuum-deposited very thin film of SubNc or SubPc₂ as electron transport layers in perovskite solar cells. In particular, we demonstrate the excellent electron extraction properties of the thin films in contact with perovskite layer. The fabricated perovskite solar cells exhibit enhanced device performances with reduced hysteresis index and improved device stability. Our results validate the use of $\pi$-extended subporphyrinoids as promising candidates for perovskite optoelectronics with enhanced stability properties, being essential for further commercialization of the perovskite technology.

Phthalocyanines (Pcs) and related macrocycles (azaporphyrinoids) are well-known artificial dyes in modern material chemistry. Several strategies for fine-tuning their optical/electrochemical/aromatic properties have been proposed. The diversity of Pcs enables novel functionalities that can assist in innovative approaches to tune and improve the properties of diverse material. Organic synthesis yields a wide array of organic molecules. Herein, the author describes two methods for developing controlled reactions in organic synthesis: controlled reactions to produce novel Pcs and controlled reactions using Pcs. In particular, the author proposes an “element-based” design strategy to obtain unique properties using a simple synthetic procedure. This strategy permits the fine-tuning of optical properties in the near-infrared (NIR) region (700–1000 nm). These innovations should create further opportunities for flexible applications of NIR light

Novel site-selective hetero-copper(II)/zinc(II) complexes of a cisoid-configured doubly N-confused dioxohexaphyrin analog (c-ZnCu-2 and c-CuZn-2) were synthesized and characterized. The resulting heterometal complexes exhibited a unique near-infrared (NIR) absorption feature, and the facile redox-active properties originated from the large 26$\pi$-conjugated structure. The distinct difference between the site-dependent c-ZnCu-2 and c-CuZn-2appeared in the specific structural parameters of the d⁹ copper centers in the electron paramagnetic resonance spectra and the Lewis acidity of the zinc centers upon the base-titrations. These complexes have potential for the hetero-metal-containing $\pi$-material applications that respond to the NIR light.

Recently we have reported that 1,14-diaminated tripyrrins form a double helical structure via interstrand hydrogen bonding interaction in non-polar solvents. In this work, ethoxycarbonyl-substituted 1,14-di(arylamino)tripyrrins were prepared by nucleophilic substitution reaction. The structure has been revealed by X-ray analysis to be a ($Z$-syn, $E$-syn) conformer stabilized by intramolecular hydrogen bonding between the pyrrolic NH proton and the ester carbonyl oxygen atom. This conformer was likely formed as a meta-stable state in solution since thermal isomerization into a ($Z$-syn, $Z$-syn) conformer was observed in DMSO via NH tautomerization.

Porphyrins are molecules that have found a wide range of applications such as dyes in solar cells, for medicinal purposes in photodynamic therapy, and as efficient catalysts in different organic transformations. In addition, the ability of porphyrins to coordinate with most metals of the periodic table provides a unique opportunity to tune the electronic properties of the macroheterocycle and thus their potential activity as catalysts. That is why, this paper reviews the recent literature and relevant advances in the oxidation of olefins catalyzed or mediated by metalloporphyrins, covering mainly those of iron and manganese because they are the most used derivatives for this process, even though other selected metal derivatives will be discussed alongside. Hence, relevant aspects of the porphyrin-mediated epoxidation reactions, such as the porphyrin activity, relevant oxidants, solvent systems, and mechanistic studies to better understand the role of porphyrins in the oxidation of olefins will be presented.

The structure of the most optimal acidic ionic liquids for the tetraphenylporphyrin synthesis was investigated, focusing on the cationic structure of ionic liquids. The investigation in [${\text{HC}}_{\text{n}}$im][CF₃CO₂] ($n$=1-12) with different lengths of alkyl groups at the N(1) position of imidazolium showed that the highest yield of tetraphenylporphyrin (20%) was obtained when the alkyl chain length was C8, which indicated that [HC₈im][CF₃CO₂] is the optimal ionic liquid for the tetraphenylporphyrin synthesis. In addition, we also investigated the influence of electron-withdrawing and electron-donating substituents at the C(2), C(4), and C(5) positions of the imidazolium cation of the acidic ionic liquids on the synthesis of tetraphenylporphyrins. The highest tetraphenylporphyrin yields were obtained in [HC₈mim][CF₃CO₂], which suggested that the imidazolium cation with an octyl group at the N(1) position and a methyl group at the C(2) position was the optimal structure.

Newly metallo-phthalocyanines substituted MPc1 of zinc, copper, and palladium, bearing 3-((2,6-di(pyridin-3-yl)-phenoxy) substituent at $\alpha$-position (non-peripheral) were synthesized and characterized by common spectroscopic methods such as ¹H-NMR, IR-FTR, MS, UV-Visible and florescence emission. Flowing several synthetic routes, the yield was increased in the series of metals: from CuPc1, PdPc1, to ZnPc1 and from ZnPc1, to ZnPc2, to ZnPc3, compared with their analogies in the literature. Afterwards, the effect of changing metals and substituents’ positions increased the Q-band value and florescence emission from PdPc1 to CuPc1 to ZnPc1 and from ZnPc2 ($\beta$-position) to ZnPc3 (octa-position), to ZnPc1($\alpha$-position) and from cationic phthalocyanines ZnPc 2Me to ZnPc 3Me to ZnPc 1Me. The study of aggregation tendance in DMSO was examined in different concentrations to confirm that there was no aggregation appearance.

Polyporphyrin films based on 5,10,15,20-tetrakis(4-pyridyl)porphyrin and 5,10,15,20-tetrakis(4-aminophenyl)porphyrin were obtained by electrochemical polymerization during the electrooxidation of the respective monomers. The polyporphyrin formation involved the side substituents, with the $\pi$-conjugated porphyrin platform being preserved. The obtained polyporphyrins form uniform electroconductive coatings, tightly adhered to the electrode surface. The electrochromic properties were studied by the spectroelectrochemical method. Electronic absorption spectra of the films were recorded under the action of electric current at the stepwise potential changes within several intervals. The obtained polyporphyrin films were shown to possess electrochromic properties. The films were oxidized when exposed to anodic potentials and reduced when exposed to cathodic potentials. The electronic absorption spectra were used to calculate the optical band gap of the initial, oxidized and reduced films and to evaluate their conductivity. The highest conductivity was found in the electrochemically oxidized poly-5,10,15,20-tetrakis(4-aminophenyl)porphyrin film.

Antipodal β-diformyl porphyrin (H₂TPP(CHO)₂) and its metal complexes (MTPP(CHO)₂, M = ${\text{Co}}^{\text{II}}$, ${\text{Ni}}^{\text{II}}$, ${\text{Cu}}^{\text{II}}$, and ${\text{Zn}}^{\text{II}})$ are synthesized and characterized by various spectroscopic techniques. Diformyl porphyrins possess two electron-withdrawing formyl substituents at their β-pyrrole positions making them electron-deficient macrocycles. UV-Vis absorption spectra of MTPP(CHO)₂ are red-shifted as compared to β-monoformyl/hydroxymethyl porphyrins and a further large anodic shift ($\mathrm{\Delta }$${\text{E}}_{1/2}$ = 0.15 - 0.52 V) was observed in their redox potentials. Hammett plots of MTPP(X)(Y) (X = CHO, CH₂OH; Y = H, CHO) showed that the HOMO-LUMO energy gap decreases with the increment in the Hammett parameter ($\sigma )$ of the substituents. DFT studies are performed for different positional isomeric diformyl porphyrins which reveal that the position of β-formyl groups affects the geometry of the porphyrin core while the symmetrical nature of 2,13-diformyl porphyrin and longer distance between two formyl groups bring quasiplanar conformation of the diformyl porphyrin macrocycle.

$N,N$-bis (4′-tert-butylbiphenyl-4-yl)aniline) tethered zinc porphyrins, (BBA)₄- ZnP, (BBA- Ph)₄- ZnP, and (BBA- OEtOPh)₄- ZnP with varied spacer distances have been synthesized and photosynthetic antenna-reaction center models were constructed via axial co-ordination with fulleropyrrolidines, C₆₀Im and C₇₀Im. Selective excitation of the BBA moiety in the porphyrins at 355 nm resulted in the quenching of the emission intensity of the BBA followed by the concomitant appearance of the ZnP emission at 600–640 nm indicating the occurrence of the photoinduced energy transfer from ¹BBA^* to ZnP. When the zinc porphyrins are titrated with C₆₀Im and C₇₀Im, supramolecular complexes of the type, (BBA)₄-ZnP:${\text{C}}_{60}$Im/${\text{C}}_{70}$Im are formed and the complex formation was monitored by UV-visible spectroscopic studies. Steady-state fluorescence studies involving the excitation of the ZnP at 550 nm displayed the diminished fluorescence intensity of the ZnP emission indicating the photoinduced electron transfer from ¹ZnP^* to fullerenes. More interestingly, when the BBA moiety is excited in the supramolecular complexes, the emission of both the BBA and ZnP were decreased gradually indicating the occurrence of PEnT from ¹BBA^* to ZnP followed by a sequential electron transfer from ¹ZnP^* to C₆₀Im or C₇₀Im indicating the formation of a charge-separated state in these complexes.

The room-temperature phosphorescence (RTP) of metalloporphyrins, induced by the heavy atom effect (HAE), has been widely concerned in many fields, and the intense emission of RTP is highly desired. The phosphorescent transition rate ($k_P)$ has been used to quantitatively characterize the HAE’s intrinsic nature. However, the phosphorescent intensity was not determined by $k_P$ alone, non-phosphorescent transition ($k_{nP})$ induced by surrounding factors was also involved. In this study, the influence of $k_{nP}$ on the RTP of palladium octaethylporphyrin (PdOEP), platinum octaethylporphyrin (PtOEP), and platinum tetraphenylporphyrin (PtTPP) was studied. The effect of $k_{nP}$ can be quantitatively described by an introduced parameter $\eta$, which was defined as $\eta$ = $k_P$/($k_P+k_{nP})$. The method is proposed for determining the $\eta$ of PdOEP, PtOEP, and PtTPP by the UV-visible absorption spectra, luminescence spectra, and phosphorescence dynamic curves. Our research provides a way to understand the effect of knP on the RTP, and may benefit the development and optimization of metalloporphyrins aiming at intense RTP.

The enzyme heme oxygenase (HO) plays an essential role in the destruction of heme molecules. Heme oxygenase uses dioxygen to open the specific orientation of the porphyrin ring at the position of the $\alpha$-meso carbon. This reaction is called mesohydroxylation, which produces $\alpha$-bilirubin, and the $\alpha$-bilirubin produced by the second enzyme bilirubin reductase is converted into bilirubin. The destruction of heme is carried out by a special enzymatic process, and the enzymes heme oxygenase and bilirubin reductase are responsible for the enzymatic role of this process. All calculations were done using Gaussian 2003 and Gaussian 2009 on an Asus NW522 computer and with the help of the Gaussian viewer, and Hyperchem software. Calculation and optimization of different configurations of molecules using the quantum computing method from the beginning of B3LYP were performed using the 631G-basis set using the FOPT keyword. The calculation of charge and spin was done based on Mulliken’s charge and spin. The analysis of bonding orbitals (NBO) was done to fully investigate the distribution of $\alpha$ and $\beta$ spins in d orbitals of iron and ring. The molecule is optimized using the quantum calculation method from the beginning, B3LYP with the basis set 6-31G. The results of DFT studies showed that the LUMO-HOMO energy gap values reflect the chemical activity of the molecule. The higher the HOMO-LUMO energy gap, the harder and more stable the molecule is and the less reactive it is. The reduction of the HOMO and LUMO energy gap explains the final charge transfer interaction that occurs inside the molecule due to the ability to accept electrons in the electron acceptor group.