Journal of Porphyrins and Phthalocyanines

The direct insertion of carbon dioxide (CO₂) into three-membered rings, such as epoxides and aziridines, represents a relevant strategy to obtain cyclic carbonates and oxazolidinones, which are two useful classes of fine chemicals. The synthesis of these compounds can be efficiently catalyzed by a combination of metal porphyrin complexes and various co-catalysts in homogeneous systems. The catalytic efficiency of these systems is discussed herein by taking into account both the characteristics of the metals and the nature of the co-catalysts, either when used as two-component systems or when combined in bifunctional catalysts. Moreover, mechanistic proposals of the CO₂ cycloaddition processes are reported to provide a rationale of catalytic cycles in order to pave the way for designing more active and efficient catalytic procedures.

This review article briefly describes the available synthetic approaches for meso-arylporphyrins giving particular emphasis for one-pot nitrobenzene and nitrobenzene/NaY methods regarding the synthesis of meso-halogenated arylporphyrins. The review also describes the relevant applications of these halogenated porphyrins and their metalloporphyrin counterparts, prepared via nitrobenzene method, as photosensitizers for therapy (PDT and PDI), diagnostic (molecular contrast agents) and also for catalytic oxidation and CO₂ cycloaddition reactions to epoxides.

Photodynamic therapy has become of interest in many European countries. Since, most of national authorities and all medical journals require the registration of the clinical study on the database ClinicalTrials. gov in order to be published, information regarding clinical studies are now available. This article aims to synthetize data gathered thanks to this database. The keywords used for this analysis was: (i) status: “All studies “(recruiting, completed, terminated, we did not take into account unknown status), (ii) condition or disease: “Photodynamic Therapy”, (iii) country: name of each European country. Since 2003, 76 clinical trials were registered in Europe. Most clinical studies are performed in Germany (22), France (20) and UK (19). These 3 countries represent 80% of all studies performed in Europe. However 21 European countries have one or more studies on PDT. Clinical studies were mainly performed on skin. Actinic Keratosis treatment (20 studies) represents more than 45% of all studies. 21% were focused on eye, mainly on Age Macular Degeneration (AMD) (8 studies). In 2018, ten (10) clinical trials are in the recruitment phase. On November, 10, 2017, Padeliporfin (STEBA Biotech S.A, Luxembourg) obtained the marketing authorization throughout the European Union. Despite the critical importance of trial registration, compliance with requirements from governmental regulators which mandate the prospective registration of clinical trials has been imperfect. Besides, a large proportion of registry entries are never updated to reflect study completion. However, this review clearly demonstrated that PDT is progressively used in most European countries.

The intermediates operating in the cytochrome P450 catalytic cycle have been investigated for more than half a century, fascinating many enzymologists. Each intermediate has its unique role to carry out diverse oxidations. Natural time course of the catalytic cycle is quite fast, hence, not all of the reactive intermediates could be isolated during physiological catalysis. Different high-valent iron intermediates have been proposed as primary oxidants: the candidates are compound 0 (Cpd 0, [FeOOH]${}^{2+}$P450) and compound I (Cpd I, Fe(IV)$=$O por${}^{•+}$P450). Among them, the role of Cpd I in hydroxylation is fairly well understood due the discovery of the peroxide shunt. This review endeavors to put the outstanding research efforts conducted to isolate and characterize the intermediates together. In addition to spectral features of each intermediate in the catalytic cycle, the oxidizing powers of Cpd 0 and Cpd I will be discussed along with most recent scientific findings.

Porphyrins are tetrapyrrolic aromatic macrocycles and ubiquitous in nature. They are excellent dyes with strong absorption in the visible region (400–700 nm) and they exhibit decent fluorescence in the red region (620–900 nm). Carbazole is a nitrogen-containing electron rich aromatic heterocycle which can be linked to porphyrins and other chromophores. This review provides an overview of the different synthetic strategies that have been employed to prepare carbazole-substituted porphyrins and carbazole-fused porphyrinoids and similar systems. It also shows that how the substitution of carbazole occurs on the porphyrin core can alter its optical and electronic features. Introduction of carbazole moieties in the porphyrin ring resulted in fused porphyrinoids with changed aromaticity and significantly altered electronic features of the molecules.

This minireview describes the complexity of the molecular mechanisms involved in the tumor response to photodynamic treatment (PDT). Different aspects of reactive oxygen (ROS) and nitrogen species (RNS) induced by PDT will be examined. In particular, we will discuss the effect of ROS and RNS on cell compartments and the main mechanisms of cell death induced by the treatment. Moreover, we will also examine host defense mechanisms as well as resistance to PDT.

Several families of herbicides, especially diphenyl ether (DPE) and pyrimidinedione, target the plant tetrapyrrole biosynthesis pathways and in particular one key enzyme, protoporphyrinogen IX oxidase (PPO). When plants are treated with DPE or pyrimidinedione, an accumulation of protoporphyrin IX, the first photosensitizer of this pathway, is observed in cytosol where it becomes very deleterious under light. Indeed these herbicides trigger plant death in two distinct ways: (i) inhibition of chlorophylls and heme syntheses and (ii) a huge accumulation of protoporphyrin IX in cytosol. Recently, a strategy based on plant transgenesis that induces deregulation of the tetrapyrrole pathway by up- or down-regulation of genes encoding enzymes, such as glutamyl-$t$RNA reductase, porphobilinogen deaminase and PPO, has been developed. Against all expectations, only transgenic crops overexpressing PPO showed resistance to DPE and pyrimidinedione. This herbicide resistance of transgenic crops leads to the hypothesis that the overall consumption of herbicides will be reduced as previously reported for glyphosate-resistant transgenic crops. In this review, after a rapid presentation of plant tetrapyrrole biosynthesis, we show how only PPO enzyme can be the target of DPE and how transgenic crops can be further resistant not only to herbicide but also to abiotic stress such as drought or chilling. Keeping in mind that this approach is mostly prohibited in Europe, we attempt to discuss it to interest the scientific community, from plant physiologists to chemists, who work on the interface of photosensitizer optimization and agriculture.

Non-peripherally substituted metal-free and zinc phthalocyanines (Pcs) bearing four diethylamino groups and four Br atoms were prepared. Optimal conditions for synthesis of corresponding precursor ($i.e.$ 3-bromo-6-(diethylamino)phthalonitrile) either by nucleophilic substitution or by Buchwald–Hartwig coupling were studied. Noteworthy, 3,6-bis(diethylamino)phthalonitrile was also formed, nevertheless only at low yield (typically below 1%) and all attempts for its cyclotetramerization failed. Q bands of prepared Pcs were strongly red shifted up to the near-IR region (769 and 800 nm in THF for zinc and metal-free Pc, respectively). Unusually large hypsochromic shifts of the Q bands, 130 and 80 nm for metal-free and zinc Pc, respectively, were observed upon treating these Pcs with trifluoroacetic acid, which was attributed to the protonation of non-peripheral amines. Treatment with sulfuric acid led to subsequent protonation on the azomethine nitrogens as well. Photophysical study revealed low fluorescence emission of both derivatives (${\mathrm{\Phi }}_F$ <0.03, in THF) and efficient singlet oxygen production only for zinc Pc (${\mathrm{\Phi }}_{\mathrm{\Delta }}=$ 0.77 in THF and 0.60 in DMF).

A series of glycosylated photosensitizers (porphyrin, chlorin, and isobacteriochlorin) in the presence of plasma proteins: bovine serum albumin (BSA) and human serum albumin (HSA), were investigated in a buffer at pH 7.4, using ultraviolet-visible (UV-vis) absorption and fluorescence spectroscopies. Due to the excitation of the tryptophan residue of BSA and HSA, its fluorescence emission was monitored around 340 nm. During each titration experiment and with each addition of the corresponding glycosylated photosensitizer, there was a concentration-dependent quenching of the intrinsic fluorescence of BSA and HSA. Using Stern–Volmer and double logarithmic plots we determined that fluorescence quenching was static for all molecules. We calculated the average binding constant for BSA and HSA for each porphyrin-type compound. To support our experimental studies, computational molecular docking and molecular dynamics simulations were used to identify the binding sites and binding poses of the each of the glycosylated photosensitizers onto BSA and HSA. The three compounds are binding to the Hemin site located in the subdomain IB of BSA forming strong interactions with Trp134, while they are binding to the subdomain IIA of HSA close to the Sudlow’s site I, and interacting with Trp214.

A clam-shaped molecule comprising a Zn(II)-porphyrin and a Zn(II)-cyclam is synthesized and characterized. Its electrochemical behavior and catalytic activity for homogeneous electrochemical reduction of carbon dioxide (CO${}_2)$ are investigated by cyclic voltammetry and compared with those of Zn(II)-meso-tetraphenylporphyrin and Zn(II)-cyclam. Under N₂-saturated conditions, cyclic voltammetry of the featured complex has characteristics of its two constituents, but under CO₂-saturated conditions, the target compound exhibits significant current enhancement. Iterative reduction under electrochemical conditions indicated the target compound has improved stability relative to Zn(II)-cyclam. Controlled potential electrolysis demonstrates that, without addition of water, methane (CH${}_4)$ is the only detectable product with 1% Faradaic efficiency (FE). The formation of CH₄ is not observed under the catalysis of the Zn(II)-porphyrin benchmark compound, indicating that the CO₂-capturing function of the Zn(II)-cyclam unit contributes to the catalysis. Upon addition of 3% v/v water, the electrochemical reduction of CO₂ in the presence of the target compound gives carbon monoxide (CO) with 28% FE. Dominance of CO formation under these conditions suggests enhancement of proton-coupled reduction. Integrated action of these Zn(II)-porphyrin and Zn(II)-cyclam units offers a notable example of a molecular catalytic system where the cyclam ring captures and brings CO₂ into the proximity of the porphyrin catalysis center.

Stable porphyrin films expressing specific chirality at a supramolecular level have been achieved by Langmuir–Blodgett (LB) deposition of two inherently chiral (L)-proline porphyrin derivatives. Spectroscopic measurements (UV-vis, CD and fluorescence) evidenced that the stereogenic center stored on the peripheral proline residue dictates the specific supramolecular organization of the macrocycles at the air/water interface, which is found to be significantly different from that observed in solution ($i.e.$ EtOH/H₂O 25/75, v/v solvent mixture). In the case of free-base porphyrin, the firmness as well as the homogeneity of the corresponding chiral LB films are not optimal for a number of layers below 10. For the zinc derivative, thermal annealing helps to make the films more oriented and produces an amplification of the chirality of the treated films. The results described are of relevance, for example, for the development of stereoselective sensors, where the fabrication of chiral surfaces with specific and reproducible stereochemistry represents a crucial issue.

Two novel axially-substituted asymmetric silicon (IV) phthalocyanines, the first one substituted with both polyethylene glycol and indomethacin groups (Pc1) and second one substituted with both polyethylene glycol and mefenamic acid groups (Pc2) have been designed and synthesized for the purpose of pH sensing examinations. Their absorption and fluorescence emission-based spectral properties were investigated in chloroform, tetrahydrofuran and toluene. The pH-sensing properties of Pc1 and Pc2 were examined in detail by using UV-vis absorption and fluorescence spectroscopies in tetrahydrofuran. The effects of the substituents on the spectroscopic properties and pH-sensing behavior of these silicon phthalocyanines were revealed. Pc1 didn’t show a pH response; however, Pc2 exhibited a signal increase from pH 5.40 to 0.37 (turn on) and a drastic quenching when pH went from 0.37 to 5.40 (turn off). The protonation/deprotonation stage of the NH group of Pc2 presented fluorescence-based “on-off” type molecular switch properties.

The synthesis and characterization of novel asymmetric zinc(II) phthalocyanines (4–9) and their linking through peripheral and nonperipheral positions on the phthalocyanine ring via click coupling to alkyne-functionalized 2,3,6,7,10,11-hexakis(prop-2-ynyloxy)triphenylene core are described for the first time. These phthalocyanines (Pcs) (4–12) were characterized by elemental analysis and different spectroscopic techniques such as UV-vis, ¹H-NMR, FT-IR and mass spectroscopy. Furthermore, the utilization of thin films of novel Pcs as a sensitive layer for detection of lung cancer from exhaled human breath at room temperature under exposure to marker volatile organic compounds (VOCs) are presented. The developed sensors were tested for acetone, ethanol, $n$-hexane, toluene, chloroform and isoprene in a range of 300–14560 ppm. The obtained results have confirmed the possibility of utilization of Pc-based Surface Acoustic Wave (SAW) sensors for medical diagnosis based on exhaled breath analysis.

With the increased risk of infectious disease transmissions, photodynamic inactivation of some microorganisms for antimicrobial applications has been extensively studied in recent years. In this article, we describe the synthesis of novel photo-bactericidal materials by grafting propargylated 5,10,15,20-tetra(4-pyridyl)porphyrin on kraft pulp fibers. The grafting was carried out by a Huisgen’s 1,3-dipolar azide-alkyne cycloaddition reaction. This material has been investigated for its antibacterial properties against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. An interesting photo-bactericidal activity was shown: this material can be used to limit the growth of bacteria on surfaces and the formation of biofilms.

Iron(III) phthalocyaninate decorated with crown ether substituents, [(15C5)₄PcFe]Cl, efficiently catalyzed the insertion of carbene derived from ethyl diazoacetate to six amines functionalized with thiazole, thiazoline and thiadiazole heterocycles. The reactions were carried out under practical conditions using EDA:amine stoechiometric ratio with 0.05 mol% catalyst loading. Turnover numbers up to 3360 have been achieved. The aminoacid derivatives bearing heterocyclic moieties were obtained under catalytic conditions for the first time with 36–69% yields in the case of single N–H insertion products and up to 77% in the case of double N–H insertion products.

Two asymmetrical amphiphilic phthalocyanines simultaneously containing hydrophobic alkoxy and hydrophilic 15-crown-5-ether substituents at the phthalocyanine periphery H₂{Pc(15C5)₃[(OC₈H${}_{17}{)}_2$]}(Pc-1) and H₂{Pc(15C5)[(OC₈H${}_{17}{)}_6$]}(Pc-2) and their symmetrical analogue H₂[Pc(OC₈H${}_{17}{)}_8$] (Pc-3) have been synthesized and characterized. The Pc-n/CdS ($n=$ 1, 2 and 3, respectively) hybrid films are obtained successfully via a simple quasi-Langmuir–Shäfer (QLS) method using H₂S-vapor annealing over the Pc-n/Cd${}^{2+}$ self-assembled film formed at the interface of the air/CdCl₂ aqueous solution. The film-structure and properties of both the hybrid Pc-n/CdS and pure Pc-n films are comparatively studied by a wide range of methods including UV-vis, polarized UV-vis, XRD, SEM and I–V measurements. Experimental results exhibit a slipped co-facial stacking mode in an “edge-on” conformation ($H$-type aggregate) formed for the phthalocyanine molecules in both pure Pc-n films and the corresponding Pc-n/CdS hybrid films, with increasing intermolecular $\pi$–$\pi$ interactions in the order of Pc-n <Pc-n/CdS and Pc-3/CdS <Pc-2/CdS <Pc-1/CdS, respectively. Accordingly, film-microstructures, crystallinity and conductivity are effectively improved by introducing CdS nanoparticles into the 15-crown-5-substituented phthalocyanines forming Pc-1/CdS and Pc-2/CdS hybrid films. These render excellent sensing performance towards NO₂ in the 0.05–2.5 ppm range within a fast dynamic exposure period of 30 s. Strikingly, Pc-1/CdS hybrid film presents an unprecedented high sensitivity of 157.3%.ppm${}^{-1}$ vs. very low NO₂ concentration range of 0.05˜0.25 ppm, achieving one of the best room temperature sensing performances in terms of high sensitivity, rapid responsibility and low detection limit among self-assembled film-based NO₂ sensors.

A pH-driven self-assembly of a simple aza-BODIPY was discovered in PBS solution, whereby ion-specific J-aggregated nanostructures were generated at very low dye concentration (2.5–20 $\mu$M). The aggregation process was investigated in different conditions (pH, temperature and time) by monitoring absorption spectral shifts and associated nanostructure morphological changes. The pH-driven self-assembly process demonstrated an instantaneous thermodynamic phenomenon associated with three characteristic structures, each with distinctive optical properties. When the sample was first formulated within a short time window, a thermodynamically less stable intermediate with an unusual morphology of triangular nanoplates and broad absorption was observed. The formation of these structures was independent of the ions in PBS solution (Na${}^{+}$, K${}^{+})$, thus indicating that the triangular structure was inherent to the anisotropic structure of aza-BODIPY scaffolds. The second structure associated with a metastable pathway generated a uniform population of spherical nanovesicles, while the third structure, generated through a more thermodynamically stable pathway consisted of fibers. The absorption spectra suggested that both spherical and fiber structures contributed to the J-aggregation band at 735 nm in the near infrared optical spectrum and their population in each formulation was concentration dependent. The results highlighted the significance of ion effects in self-assembly of aza-BODIPY and the mechanistic structural changes of the morphology. Furthermore, this fundamental discovery offers a versatile method for the self-assembly of aza-BODIPY J-aggregates as a new nanoplatform with potential photonic applications.

Porphyrins and metalloporphyrins are one of the most widely studied platforms for the construction of supramolecular structures. These compounds have an extended aromatic system that allows $\pi$–$\pi$ stacking interactions which, together with hydrogen bonds, electrostatic forces and the formation of inter-metallic complexes arising from peripheral groups, offer a versatile platform to control the self-assembly mechanism. In this work, we present the study of nanostructures formed by self-assembly of the water-soluble porphyrins meso-tetra($N$-methyl-4-pyridyl)porphyrin (TMPyP) and meso-tetra(4-sulfonatophenyl)porphyrin (TPPS) in the presence of hard nanotemplates. Different nanoparticles (silica, gold, and polystyrene), concentrations and synthetic procedures were explored. The obtained materials were characterized by SEM and AFM microscopies, UV-vis absorption spectroscopy and dynamic light scattering measurements. A clear modification of the SiO₂ NP surface roughness using one-pot synthesis was observed. The results were variable depending on the porphyrin–surface interactions and concentrations used. At lower porphyrin concentrations, a shift of the Soret band was observed, while at higher concentrations, free NS were formed. This reflects a competition between surface and solution directed self-assembly.

The increasing world-wide rate of antibiotic resistance as well as the capacity of microorganisms to form biofilms, have led to a higher incidence of mortal infections that require alternative methods for their control. Antimicrobial photodynamic therapy (aPDT) emerged as an effective solution against resistant strains. The present work aims to evaluate the aPDT efficiency of a photosensitizer (PS) based on a low-cost formulation constituted by five cationic porphyrins (FORM) and its potentiation effect by KI on a broad spectrum of microorganisms under white light (380–700 nm, 25 W/m${}^2)$. The aPDT assays were performed with different concentrations of FORM (0.1 to 5.0 $\mu$M) and 100 mM of KI on planktonic and biofilm forms of gram-positive (methicillin resistant Staphylococcus aureus–MRSA) and gram-negative (Escherichia coli resistant to chloramphenicol and ampicillin) bacteria, of the fungi Candida albicans and on a T4-like bacteriophage as a mammalian virus model. The results indicate that the FORM alone is an efficient PS to photoinactivate not only gram-negative and gram-positive bacteria, but also C. albicans, in planktonic and biofilm forms, and T4-like phage at low concentrations (<5.0 $\mu$M). The presence of KI enhanced the photodynamic effect of this FORM for all microorganisms on the planktonic form, allowing the reduction of PS concentration and treatment time. The results also show that the combination FORM/KI is highly efficient in the elimination of already well-established biofilms of E. coli,S. aureus and C. albicans. This effect is probably associated with longer-lived iodine reactive species produced during the aPDT treatment.

The synthesis and characterization of a $p$-phenylene-bridged ZnPc dimer along with a preliminary study of this material as hole transporting material (HTM) in perovskite solar cells is described. The maximum efficiencies that obtained are 15.2% for ZnPc-$p$-ZnPc 1, thus demonstrating the potential of the Pc dimers that could pave the path to achieve highly efficient PSCs (PCE >20%).

Cobyric acid and cobinamide are valuable building blocks for the synthesis of artificial cobalamins modified at the nucleotide loop. However, truncated vitamin B${}_{12}$ derivatives are devoid of the phosphate group. We have found that 2-iodoxy benzoic acid-mediated phosphorolysis leads to the cleavage of only one of the phosphodiester bond giving a vitamin B${}_{12}$ analogue with the phosphate moiety preserved. Subsequent alkylation with an organic halide establishes its role as a precursor for the synthesis of vitamin B${}_{12}$ mimics modified at the nucleotide loop.

CoPc(COOH)${}_4$-TiO${}_2$ nanocomposites to be used as efficient visible light photocatalysts were obtained by modifying TiO₂ nanoparticles with cobalt(II) tetracarboxyphthalocyanine (CoPc(COOH)${}_4$). The photocatalyst was then characterized by ultra-violet diffuse reflectance spectroscopy (UV-DRS), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The UV-DRS spectra showed that the absorbance spectrum of the modified catalyst was shifted to the visible region. Different textile dye solutions of Reactive Red 180, Acid Red 88 and Direct Orange 46 were efficiently degraded under visible light. Color removal rates were established to be 30%, 53% and 47% after 180 min for RR180, AR88 and DO46 dyes, respectively. The optimum catalyst concentration was determined to be 1 g/L of CoPc(COOH)${}_4$-TiO${}_2$. Development of the CoPc(COOH)${}_4$-TiO${}_2$ nanocomposite photocatalyst enabled the utilization of visible light irradiation for efficient photodegradation of organic textile dye solutions.

A water soluble, phenanthroline-strapped zinc porphyrin bearing four arylsulfonate groups formed a stable host–guest complex with two per-$O$-methylated $\beta$-cyclodextrin cavities. In the host–guest assembly, the zinc porphyrin was capable of binding imidazole within the cavity between the zinc(II) ion and the phenanthroline strap in an aqueous medium. The formation of a hydrogen bond between the imidazole NH and the nitrogen atoms of the phenanthroline was an essential element of the binding event, as shown by comparative binding studies with a non-strapped tetrasulfonated zinc porphyrin and with $N$-methylimidazole. This hydrogen bonding in an aqueous medium was possible due to the protected hydrophobic environment created by the cyclodextrins around the phenanthroline strap. This type of binding event may provide a biomimetic approach to study water soluble heme protein models.

4-[4-(1-Methyl-1-penylethyl)phenoxy]- and 4,5-di-[4-(1-methyl-1-phenylethyl)phenoxy]phthalonitriles are obtained by nucleophilic substitution. Mono- and double-decker lutetium and erbium complexes of 2(3),9(10),16(17),23(24)-tetrakis- and 2,3,9,10,16,17,23,24-octakis-[4-(1-methyl-1-phenylethyl)phenoxy]phthalocyanines are synthesized based on the phthalonitriles. Synthesized complexes are studied spectrophotometrically.

Tetraphenylporphyrin derivatives a synthetic heterocycles with convenient preparation and a richness of properties which make them attractive in broad fields such as energy, life and materials sciences. Thus, in the quest for new radical architectures, tetraphenylporphyrins are prime candidates. To this end, we designed free-base tetraphenylporphyrins bearing nitronyl and imino nitroxide moieties covalently bonded to the para-position of the meso-phenyl substituent. Their detailed synthesis and characterization are reported here.

Unlike N-confused porphyrins which are well-known and extensively studied tetrapyrroles, N-confused hydroporphyrins are almost unknown, largely because so far they have resisted attempts at rational synthesis. Here, we report our efforts towards the total synthesis of N-confused hydroporphyrins. We have prepared N-confused building blocks analogous to the non-N-confused substrates in the Lindsey synthesis of sparsely substituted chlorins. We have systematically flipped the A, B and C pyrrole rings in the dipyrrolic precursors of the target N-confused macrocycles, preparing in total an N-confused “Western half” (tetrahydrodipyrrin) and two N-confused “Eastern halves” (brominated formyldipyrromethanes). These were subjected to a range of cyclization conditions. While we successfully isolated and identified three macrocyclic products, none of these proved to be the desired N-confused hydroporphyrin.

The first example of A2B2 tetrabenzoporphyrin (KW-4) was synthesized, characterized and evaluated as a sensitizer for dye-sensitized solar cells. UV-vis and fluorescence spectroscopy revealed red-shifted and broadened absorption spectra of A2B2 tetrabenzoporphyrin as compared with its A2 dibenzo- and A2B2 dibenzoporphyrin analogues, which is a desired feature of dyes for dye-sensitized solar cells. DFT calculations also indicate favorable electron density distribution on the HOMO and LUMO of KW-4. However, the power conversion efficiency of the solar cell based on tetrabenzoporphyrin KW-4 displayed inferior performance than that of the solar cell based on A2 dibenzoporphyrin KW-2. The lower performance of the KW-4 cell was ascribed to two factors: the low lying LUMO energy level leading to less efficient electron injection and the “flat geometry” of the dye on TiO₂ surface facilitating charge recombination and decreasing dye loading. The investigation of anchoring group effect suggests that the acrylic acid group is a better anchoring group than pentadienyl carboxylic acid.

In an attempt to investigate its potential as a PDT ${}^{19}$F MRI molecular theranostic, a Zn phthalocyanine with 24 pseudo-equivalent fluorine atoms was designed and prepared. Compared to its H analogues, the fluorinated derivative has a much higher generation of singlet oxygen. ${}^{19}$F NMR signals in CDCl₃ showed that all the fluorine atoms are magnetically pseudo-equivalent with only two close fluorine signals. Formulation in PVP (polyvinylpyrrolidone), a FDA-approved additive, enabled water-solubilization of the phthalocyanines but no satisfying ${}^{19}$F NMR signal could be obtained, probably due to self-quenching caused by aggregation.