Synthesis, Separation and UV/Vis Spectroscopy of Pyrazino-quinoxalino-porphyrazine Macrocycles

Synthesis and J-Dimer Formation of Tetrapyrazinoporphyrazines with Different Functional Groups for Potential Biomolecular Probe Applications

Though tetrapyrazinoporphyrazines (TPyzPzs) are generally presented as universal dark quenchers for oligonucleotide probes, the availability of TPyzPzs bearing different functional groups suitable for attachment to 3', and 5' ends or intrastrand positions remains rather limited. Therefore, a synthetic route to hexa(bis(2-methoxyethyl)amino) or hexa(diethylamino) TPyzPzs functionalized by an azide, hydroxy, or carboxy group or their combinations was developed. Studies of self-assembly into J-dimers in nonpolar solvents and their stability upon titration with pyridine (association constants, K_P values, ranging 0.32-12.7×10²  M^-1 ) revealed that smaller peripheral substituents and functionalization of TPyzPzs improves the stability of J-dimers. Φ_Δ and Φ_F were low for the monomers (Φ_F <0.0001, Φ_Δ <0.008, DMF) due to quenching by intramolecular charge transfer; however, they increased in nonpolar solvents and after self-assembly into J-dimer (up to Φ_F =0.027, Φ_Δ =0.28).

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.

Synthesis and Evaluation of a Tetra[6,7]quinoxalinoporphyrazine-based Near Infrared Photosensitizer

Here we report a near infrared, water-soluble, functional and dendrimeric photosensitizer (PS) based on quinoxalinoporphyrazine structure. The photophysical properties and in vitro photodynamic therapy results suggest that this quinoxalinoporphyrazine-based dendrimer may serve as an efficient near infrared (NIR) PS platform.

Systematic investigation of phthalocyanines, naphthalocyanines, and their aza-analogues. Effect of the isosteric aza-replacement in the core

A series of zinc complexes of phthalocyanines, naphthalocyanines and their aza-analogs was studied and compared using UV-vis and MCD spectra, molecular calculations, and photophysical and electrochemical measurements.

β-Pyrazino-fused tetrarylporphyrins

A novel method for the preparation of β-fused porphyrin dyads was developed that exploits a one-pot reaction of 2,3-diaminoporphyrins with diethyl oxalate. This approach provides good yields of the zinc β-fused dyad and the corresponding free-base, opening the way for preparation of several metal derivatives to permit modulation of optoelectronic characteristics for commercial applications.

Effect of intramolecular charge transfer on fluorescence and singlet oxygen production of phthalocyanine analogues

Intramolecular charge transfer (ICT) was studied on a series of magnesium, metal-free and zinc complexes of unsymmetrical tetrapyrazinoporphyrazines and tribenzopyrazinoporphyrazines bearing two dialkylamino substituents (donors) and six alkylsulfanyl or aryloxy substituents (non-donors). The dialkylamino substituents were responsible for ICT that deactivated excited states and led to considerable decrease of fluorescence and singlet oxygen quantum yields. Photophysical and photochemical properties were compared to corresponding macrocycles that do not bear any donor centers. The data showed high feasibility of ICT in the tetrapyrazinoporphyrazine macrocycle and significantly lower efficiency of this deactivation process in the tribenzopyrazinoporphyrazine type molecules. Considerable effect of non-donor peripheral substituents on ICT was also described. The results imply that tetrapyrazinoporphyrazines may be more suitable for development of new molecules investigated in applications based on ICT.

Solid-phase synthesis of azaphthalocyanine-oligonucleotide conjugates and their evaluation as new dark quenchers of fluorescence

Hydrophobic nonaggregating metal-free azaphthalocyanines (AzaPc) of the tetrapyrazinoporphyrazine type were synthesized, characterized, and used for oligonucleotide labeling. Both 3'-end and 5'-end labeling methods using solid phase synthesis suitable for automatic processes in the DNA/RNA synthesizer were developed. The hydrophobic character of AzaPc enabled the anchoring of the conjugates on reverse phase of the oligonucleotide purification cartridge, thus enabling their simple purification. AzaPc did not show any fluorescence and extremely low singlet oxygen quantum yields (Φ(Δ) = 0.015-0.018 in DMF) in a monomeric state due to ultrafast intramolecular charge transfer. That is why they were investigated as a new dark quencher structural type. They profit particularly from absorption in a wide range of wavelengths (300-740 nm) that covers all fluorophores used in hybridization assays nowadays. As an example, quenching efficiency was evaluated in a simple hybridization assay using monolabeled probes. AzaPc-based probes efficiently quenched both fluorescein and Cy5 fluorescence by both resonance energy transfer and contact quenching. The results were compared with three established dark quenchers, and the AzaPc exerted better (BHQ-1 and BHQ-2) or comparable (BBQ-650) quenching efficiencies for both fluorophores.

Synthesis, properties and in vitro photodynamic activity of water-soluble azaphthalocyanines and azanaphthalocyanines

In this work zinc azaphthalocyanines (AzaPcs) from the group of tetrapyrazinoporphyrazines and zinc azanaphthalocyanines from the group of tetra[6,7]quinoxalinoporphyrazines (TQP) with eight diethylaminoethylsulfanyl substituents were synthesized. Tertiary amines were later quaternized with ethyl iodide to obtain water-soluble photosensitizers (PSs). Quaternized compounds showed high singlet oxygen quantum yields as determined in DMF by monitoring decomposition of 1,3-diphenylisobenzofuran. In water medium, quaternized AzaPc derivatives appeared in monomeric form in a wide range of concentrations while quaternized TQP derivatives showed aggregation at higher concentrations (over 1 microM). Photodynamic activity was tested on Hep2 cells using light of lambda > 640 nm. Both quaternized dyes showed high photodynamic activity (IC(50) = 104 and 220 nm for AzaPc and TQP, respectively). Dark toxicity was not detected even at the highest concentration used in in vitro tests (200 microM) which indicates a promising therapeutic index of these new substances. Tested compounds localized inside the cells mainly within the lysosomes thus suggesting an endocytic mechanism of cellular uptake. No localization within mitochondria was detected. A great advantage of TQP derivatives over other PSs is their very strong absorption at 747 nm that allows activation at wavelengths penetrating deeper into human tissues.

Effective Monofunctional Azaphthalocyanine Photosensitizers for Photodynamic Therapy

In this work we present a rational design of the active part of third generation photosensitizers for photodynamic therapy based on phthalocyanine and an azaphthalocyanine core. The preferred zinc complexes of the AAAB type that contain bulky tert-butylsulfanyl substituents (A) and one carboxy group (B) have been synthesized by statistical condensation and fully characterized. The tetramerization was performed using magnesium(ii) butoxide followed by demetalation and insertion of ZnII. Compound 1 synthesized from 4,5-bis(tert-butylsulfanyl)phthalonitrile (A) and 2,3-dicyanoquinoxaline-6-carboxylic acid (B) exerted very promising photophysical properties (Q-band absorption at 726 nm, ϵ = 140000 M–1 cm–1), which allowed strong absorption of light at long wavelengths where the penetration of the light through human tissues is deeper. The very high singlet oxygen quantum yield of 1 (ΦΔ = 0.80) assures efficient photosensitization. As a result of bulky peripheral substituents, compound 1 shows good solubility in organic solvents with a low degree of aggregation, which makes it potentially viable for non-complicated modification. One carboxy group in the final structure of 1 allows simple binding to possible carriers. This compound is suitable for binding to targeting moieties to form the highly active part of a third-generation photosensitizer.