Phenol-Substituted Tetrapyrazinoporphyrazines: pH-Dependent Fluorescence in Basic Media

Phosphorus(V) tetrapyrazinocorrolazines bearing axial aryloxy groups as pH-sensitive fluorophores and photosensitizers

Phosphorus(V) complexes of octaphenyltetrapyrazinocorrolazine bearing two aryloxy groups in the axial position, [TPyzCAP(OAr)₂] (2a-c, Ar = phenyl (2a), 4-dimethylaminophenyl (2b), and 4-hydroxyphenyl (2c)), were prepared using a one-pot procedure by consecutive treatment of the dihydroxidophosphorus(V) derivative, [TPyzCAP(OH)₂] (1), with SOCl₂ and then with the corresponding phenol ArOH. Complex 2a containing axial PhO groups is fluorescent in all studied solvents (toluene, CH₂Cl₂, THF, and DMSO, Φ_F ∼ 0.16-0.31) and is efficient to generate singlet oxygen (Φ_Δ = 0.55 (THF), 0.68 (toluene)). The introduction of NMe₂ and OH groups in the para-position of the axial ArO ligands strongly affects the fluorescence parameters and photosensitizing properties due to the appearance of the solvent-sensitive and pH-switchable effects of photoinduced electron transfer (PET). The PET effect of NMe₂ groups completely quenches the excited state of 2b in all solvents, but it is switched-OFF upon their protonation, and in the presence of acid traces, the fluorescence of 2b becomes bright and singlet oxygen generation is strongly enhanced. The PET effect of the OH group is increased upon its deprotonation and in the presence of base 2c as well as 1 becomes non-fluorescent. Specific solvation in THF and DMSO increases the ionic character of the OH bonds, and the fluorescence and photosensitizing properties of 1 and 2c are strongly decreased in these solvents. According to the results of DFT calculations performed using the B3LYP functional with the cc-pVDZ basis set and cyclic voltammetric studies, the molecular orbitals localized on aryloxy ligands are destabilized upon the introduction of OH and especially NMe₂ groups and their close position to the HOMO of corrolazine macrocycle (above HOMO in 2b and between HOMO and HOMO-1 in 2c) leads to the appearance of the PET effect.

Magnesium Phthalocyanines and Tetrapyrazinoporphyrazines: The Influence of a Solvent and a Delivery System on a Dissociation of Central Metal in Acidic Media

Magnesium complexes of phthalocyanines (Pcs) and their aza-analogues have a great potential in medical applications or fluorescence detection. They are known to demetallate to metal-free ligands in acidic environments, however, detailed investigation of this process and its possible prevention is lacking. In this work, a conversion of lipophilic and water-soluble magnesium complexes of Pcs and tetrapyrazinoporphyrazines (TPyzPzs) to metal-free ligands was studied in relation to the acidity of the environment (organic solvent, water) including the investigation of the role of delivery systems (microemulsion or liposomes) in improvement in their acido-stability. The mechanism of the demetallation in organic solvents was based on an acidoprotolytic mechanism with the protonation of the azomethine nitrogen as the first step and a subsequent conversion to non-protonated metal-free ligands. In water, the mechanism seemed to be solvoprotolytic without any protonated intermediate. The water-soluble magnesium complexes were stable in a buffer with a physiological pH 7.4 while a time-dependent demetallation was observed in acidic pH. The demetallation was immediate at pH < 2 while the full conversion to metal-free ligand was done within 10 min and 45 min for TPyzPzs at pH 3 and pH 4, respectively. Incorporation of lipophilic magnesium complexes into microemulsion or liposomes substantially decreased the rate of the demetallation with the latter delivery system being much more efficient in the protection from the acidic environment. A comparison of two different macrocyclic cores revealed significantly higher kinetic inertness of magnesium TPyzPz complexes than their Pc analogues.

Synthesis of axially disubstituted silicon phthalocyanines and investigation of their in vitro cytotoxic/phototoxic anticancer activities

In this study, two SiPcs have been selected and the photodynamic therapy potentials were evaluated of the Pcs. Synthesis of Axially 2-decyn-1-oxy disubstituted Es-SiPc-2 was newly synthesized by the reaction of SiPcCl2 with 2-decyn-1-ol in the presence of NaH in toluene. Furthermore, their nuclear imaging potentials were evaluated in human colon adenocarcinoma (HT-29) and human lung fibroblast cell (WI-38) cell lines. The uptake results have indicated that Es-SiPc labeled with [Formula: see text]I radionuclide ([Formula: see text]I-Es-SiPc) was approximately 2-fold higher in the HT-29 cell line than the WI-38 cell line. In other words, the target/non-target tissue ratio is defined as two in the HT-29/WI-38 cell lines. Besides, the uptake values of [Formula: see text]I-Es-SiPc were found to be higher than [Formula: see text]I-Es-SiPc-2. [Formula: see text]I-Es-SiPc and [Formula: see text]I-Es-SiPc-2 are promising for imaging or treating colon adenocarcinoma. In vitrophotodynamic therapy (PDT) studies have shown that both compounds are suitable and can be used in this field. Also, Es-SiPc has been shown to have higher phototoxicity than Es-SiPc-2.

pH-Sensitive subphthalocyanines and subazaphthalocyanines

Although subphthalocyanines (SubPcs) possess advantageous fluorescence properties and serve as an amazing tool to attach a recognition sensor moiety to the axial position, a limited number of switchable SubPcs have been described so far. Isosteric aza-replacement is known to improve sensing properties in closely related phthalocyanine families; however, pyrazino[2,3-b,g,l]subporphyrazines (SubPyzPzs) have not yet been investigated for use in sensing applications. Therefore, this project focuses on the synthesis and sensing abilities of pH-sensitive SubPcs and SubPyzPzs on the principle of photoinduced electron transfer (PET). 4-Dimethylaminophenoxy (for acidic pH) or 4-hydroxyphenoxy (for basic pH) groups were employed as pH-sensitive axial ligands. Electrochemical studies revealed improvements in the electron-accepting properties of SubPyzPzs (E_red-0.56 V vs. SCE) in comparison to those of SubPcs (E_red-1.0 V vs. SCE). Hydroxy groups on the axial phenoxy ligands of SybPyzPzs and SubPcs have been found to act as donors for PET. The sensing properties under basic conditions could not be studied, since all the SubPcs and SubPyzPzs decomposed under basic conditions, SubPyzPzs were more susceptible to this process. On the other hand, compounds with 4-dimethylaminophenoxy groups as axial ligands showed great potential for sensing applications. These compounds were nonfluorescent (Φ_F < 0.01) in acetone due to efficient PET, while their fluorescence steeply increased by two orders of magnitude upon the addition of trifluoroacetic acid, reaching a Φ_F value of up to 0.17 (λ_em range of 563-590 nm). These compounds maintained their sensing properties in aqueous medium after incorporation into microemulsions. The most basic derivative showed pK_A = 2.95 with Φ_F = 0.10 in the ON state (fluorescence enhancement factor = 46, λ_em = 577 nm).

Red-Emitting Fluorescence Sensors for Metal Cations: The Role of Counteranions and Sensing of SCN- in Biological Materials

The spatiotemporal sensing of specific cationic and anionic species is crucial for understanding the processes occurring in living systems. Herein, we developed new fluorescence sensors derived from tetrapyrazinoporphyrazines (TPyzPzs) with a recognition moiety that consists of an aza-crown and supporting substituents. Their sensitivity and selectivity were compared by fluorescence titration experiments with the properties of known TPyzPzs (with either one aza-crown moiety or two of these moieties in a tweezer arrangement). Method of standard addition was employed for analyte quantification in saliva. For K⁺ recognition, the new derivatives had comparable or larger association constants with larger fluorescence enhancement factors compared to that with one aza-crown. Their fluorescence quantum yields in the ON state were 18× higher than that of TPyzPzs with a tweezer arrangement. Importantly, the sensitivity toward cations was strongly dependent on counteranions and increased as follows: NO₃^- < Br^- < CF₃SO₃^- < ClO₄^- ≪ SCN^-. This trend resembles the chaotropic ability expressed by the Hofmeister series. The high selectivity toward KSCN was explained by synergic association of both K⁺ and SCN^- with TPyzPz sensors. The sensing of SCN^- was further exploited in a proof of concept study to quantify SCN^- levels in the saliva of a smoker and to demonstrate the sensing ability of TPyzPzs under in vitro conditions.

Magnesium tetrapyrazinoporphyrazines: tuning of the pKa of red-fluorescent pH indicators

Fluorescence of Mg(ii) complexes of tetrapyrazinoporphyrazines can be switched off and on depending on pH.

Novel phenyl-substituted pyrazinoporphyrazine complexes of rare-earth elements: optimized synthetic protocols and physicochemical properties

Novel synthetic protocols based on both template and direct methods were developed for phenyl-substituted pyrazinoporphyrazine complexes of rare-earth elements.

An experimental and computational study on isomerically pure, soluble azaphthalocyanines and their complexes and boron azasubphthalocyanines of a varying number of aza units

Herein, we present a series of isomerically pure, peripherally alkyl substituted, soluble and low aggregating azaphthalocyanines as well as their new, smaller hybrid homologues, azasubphthalocyanines. The focus lies on the effect of the systematically increasing number of aza building blocks [-N[double bond, length as m-dash]] replacing the non-peripheral [-CH[double bond, length as m-dash]] units and their influence on the physical and photophysical properties of these chromophores. The absolute and relative HOMO-LUMO energies of azaphthalocyanines were analyzed using UV-Vis and CV and compared to the density functional theory calculations (B3LYP, TD-DFT). The lowering of the HOMO level is revealed as the determining factor for the trend in the adsorption energies by electronic structure analysis. Crystals of substituted subphthalocyanines, N2-Pc*H2 and N4-[Pc*Zn·H2O], were obtained out of DCM. For the synthesis of the valuable tetramethyltetralin phthalocyanine building block a new highly efficient synthesis involving a nearly quantitative CoII catalyzed aerobic autoxidation step is introduced replacing inefficient KMnO4/pyridine as the oxidant.

Photodynamic properties of aza-analogues of phthalocyanines

Spectral and photophysical properties and in vitro photodynamic activity of aza-analogues of phthalocyanines are summarized.

Phthalocyanines and Tetrapyrazinoporphyrazines with Two Cationic Donuts: High Photodynamic Activity as a Result of Rigid Spatial Arrangement of Peripheral Substituents

High photodynamic activity was observed for hexadeca-cationic zinc, magnesium, and metal-free phthalocyanines (Pcs) and tetrapyrazinoporphyrazines with EC₅₀ values as low as 5 nM (MCF-7 cells) for the best compound; this activity was several times better than that of clinically established photosensitizers verteporfin, temoporfin, S₃AlOHPc, or protoporphyrin IX. This lead compound was characterized by low dark toxicity (TC₅₀ = 369 μM), high efficiency against other cell lines (HCT 116 and HeLa), and possible activation by light above 680 nm. The excellent photodynamic activity resulted from the rigid spatial arrangement of the quaternized triazole moieties above and below the Pc core, as confirmed by X-ray crystallography. The triazole moieties thus formed two "cationic donuts" that protected the hydrophobic core against aggregation in water. The lysosomes were found to be the site of subcellular localization and were consequently the primary targets of photodynamic injury, resulting in predominantly necrotic cell death.

Synthesis and singlet oxygen generation of pyrazinoporphyrazines containing dendrimeric aryl substituents

Singlet oxygen generation yields and aggregation tendencies were studied for porphyrazines bearing dendrimeric substituents.

OFF-ON-OFF Red-Emitting Fluorescent Indicators for a Narrow pH Window

A unique combination of two independent mechanisms of fluorescence quenching, namely intramolecular charge transfer (ICT) from a peripheral donor and protonation of azomethine nitrogen atoms in zinc tetrapyrazinoporphyrazines (TPyzPz), provides a new possibility for sensing pH in a specific range. The pH selectivity was controlled by the different basicities of the donor for ICT (dimethylaminoaryl), which was connected to the macrocycle by π-extended linkers of different lengths. ICT and protonation have been studied in detail by photophysical, spectral (UV/Vis and MCD spectra), and electrochemical measurements, and further supported by theoretical calculations (DFT, TDDFT). The pH-sensing properties of the TPyzPzs have been investigated in THF and in water after anchoring the TPyzPzs to liposomes. The salient pK_a values were around 1.3 (azomethine nitrogen) and 2.29-4.76 (donor for ICT). The lead indicators (sensing over a pH range of 1.0-2.5) with fairly steep sensing profiles exhibited increases in fluorescence between the OFF/ON states of more than 20-fold and strong absorption in the red region (Q-band maximum >650 nm, ϵ≈2×10⁶  m^-1  cm^-1 ).

Predominant effect of connecting atom and position of substituents on azomethine nitrogens’ basicity in phthalocyanines

The basicity of azomethine nitrogens was studied on a series of phthalocyanines (Pcs) that differed in a position of substituent, [Formula: see text] peripherally ([Formula: see text]-series) and non-peripherally substituted Pcs ([Formula: see text]-series), and in a type of substituent (alkylsulfanyl, alkyloxy or alkyl). Appropriate 3,6- or 4,5-disubstituted phthalonitriles were prepared either by nucleophilic substitution or by Negishi coupling. Target zinc Pcs were synthesized by Linstead method. The basicity was studied by the mean of absorption and1H NMR spectroscopies in chloroform upon titration with trifluoroacetic acid. Equilibrium constants (log [Formula: see text]) indicated significant difference within the series. Basicity decreased as follows: [Formula: see text]-alkyloxy ≫ [Formula: see text]-alkylsulfanyl > [Formula: see text]-alkyloxy > [Formula: see text]-alkyl > [Formula: see text]-alkylsulfanyl ∼ [Formula: see text]-alkyl with log [Formula: see text] higher than 7 down to 2.6 M[Formula: see text]. Increased basicity of [Formula: see text]-alkyloxy and [Formula: see text]-alkylsulfanyl Pcs is caused by the stabilization of trapped hydrogen at azomethine nitrogen via hydrogen bonding and van der Waals interactions, respectively. The basicity of [Formula: see text]-series clearly correlated with the electronic effects of substituents.1H NMR studies confirmed the possibility of the weak bonding interactions in [Formula: see text]-alkyloxy and [Formula: see text]-alkylsulfanyl Pcs, however, the position of the1H NMR signal of azomethine-NH proton was even more influenced by the electronic effects of present substituents than by the weak interactions.

OFF-ON-OFF Dual Emission at Visible and UV Wavelengths from Carbazole Functionalized β-Diketonate Europium(III) Complex

This work demonstrates dual emission "OFF-ON-OFF" switching at visible and UV wavelengths of a carbazole functionalized β-diketone (LH) by a simple change of a europium(III) ion (Eu(3+)) concentration in the submicromolar concentration range. In the presence of 0.25 equiv of Eu(3+) (5 μM), LH forms a luminescent 4:1 complex ([Eu(3+)(L(-))4](-)) exhibiting dual emission at 357 and 613 nm resulting from the local excitation of the carbazole ring and ligand-sensitized luminescence from the Eu(3+)-β-diketonate unit, respectively. The 4:1 complex begins to convert into a 2:1 complex ([Eu(3+)(L(-))2](+)) via a 3:1 complex [Eu(3+)(L(-))3] above a molar ratio ([Eu(3+)]/[LH]) of 0.25, which provides the opportunity for binding of solvent methanol molecules to the vacant site of the Eu(3+) ion in the complex ([Eu(3+)(L(-))2(MeOH)n](+)). The OH oscillators of coordinated methanol molecules facilitate the nonradiative pathway of the Eu(3+) emission; hence the emission at 613 nm almost disappears above the 0.50 equivalent of Eu(3+) (11 μM), while the UV emission at 357 nm remains mostly constant over the whole concentration range.