Effective Photosensitizer For Photodynamic Therapy Research Articles

Study of Photodegradation of Thiazion Dye Methylene Blue under Exposure to a Laser for Photodynamic Therapy

Purpose. To study the process of photodegradation of methylene blue under the influence of laser radiation with a wavelength of 660 nm, used for photodynamic therapy installations, for the formation of reactive oxygen species, in particular short-lived hydroxyl radicals, using electron paramagnetic resonance (EPR) spectroscopy.Methods. The residual concentration of methylene blue during photodegradation was determined using an HR2000 spectrometer. The formation of hydroxyl groups was detected using an EPR spectrometer SPINSCAN X.Results. Analysis of data on the photodegradation of methylene blue shows that under the influence of laser radiation with a wavelength of 660 nm, the structure of methylene blue is destroyed, manifested in the gradual discoloration of the dye solution. When trypaflavin is added to the solution, the rate of photodegradation of methylene blue slows down significantly. Analysis of ESR spectroscopy data shows that when methylene blue is exposed to a red laser, (OH’) radicals begin to intensively form in the solution. Their content increases significantly with increasing irradiation power.Conclusion. Irradiation of an aqueous solution of the thiazion dye methylene blue by a laser source with a power of 0.3÷1 W and a wavelength of 660 nm leads to its active photodegradation. The addition of trypaflavin leads to a slowdown in the process of photodegradation of methylene blue when irradiated with red light due to the consumption of part of the generated oxygen-containing radicals for the degradation of trypaflavin. According to EPR spectroscopy data using DMPO spin traps, it has been proven that when methylene blue is irradiated with a red laser, active formation of hydroxyl OH' radicals occurs. It was found that with increasing laser radiation intensity, the amount of generated hydroxyl radicals (OH') increases significantly. The presented results may contribute to the development of effective photosensitizers for photodynamic therapy of tumor tumors.

New Highly Fluorescent Water Soluble Imidazolium-Perylenediimides: Synthesis and Cellular Response.

The synthesis and characterization of two new water soluble 2,6-bis(imidazolylmethyl)-4-methylphenoxy-containing perylenediimides, PDI-1 and PDI-2, are described. These compounds demonstrate a high fluorescence quantum yield in water and were investigated as potential photosensitizers for generating reactive oxygen species with applications in anticancer activities. The HeLa cell line (VPH18) was used to evaluate their efficacy. Fluorescence microscopy was employed to confirm the successful internalization of PDI-1 and PDI-2, while confocal microscopy revealed the specific locations of both PDIs within the lysosomes and mitochondria. In vitro studies were conducted to evaluate the anticancer activity of PDI-1 and PDI-2. Remarkably, these photosensitizers demonstrated a significant ability to selectively eliminate cancer cells when exposed to a specific light wavelength. The water solubility, high fluorescence quantum yield, and selective cytotoxicity of these PDIs toward cancer cells highlight their potential as effective agents for targeted photodynamic therapy. In conclusion, the findings presented here provide a strong foundation for the future exploration and optimization of PDI-1 and PDI-2 as effective photosensitizers in photodynamic therapy, potentially leading to improved treatment strategies for cancer patients.

Quatsomes Loaded with Squaraine Dye as an Effective Photosensitizer for Photodynamic Therapy.

Photodynamic therapy is a non-invasive therapeutic strategy that combines external light with a photosensitizer (PS) to destroy abnormal cells. Despite the great progress in the development of new photosensitizers with improved efficacy, the PS's photosensitivity, high hydrophobicity, and tumor target avidity still represent the main challenges. Herein, newly synthesized brominated squaraine, exhibiting intense absorption in the red/near-infrared region, has been successfully incorporated into Quatsome (QS) nanovesicles at different loadings. The formulations under study have been characterized and interrogated in vitro for cytotoxicity, cellular uptake, and PDT efficiency in a breast cancer cell line. The nanoencapsulation of brominated squaraine into QS overcomes the non-water solubility limitation of the brominated squaraine without compromising its ability to generate ROS rapidly. In addition, PDT effectiveness is maximized due to the highly localized PS loadings in the QS. This strategy allows using a therapeutic squaraine concentration that is 100 times lower than the concentration of free squaraine usually employed in PDT. Taken together, our results reveal the benefits of the incorporation of brominated squaraine into QS to optimize their photoactive properties and support their applicability as photosensitizer agents for PDT.

Pentacene Nanorods as Effective Photosensitizer for Photodynamic Therapy of Tumor via Singlet Fission

AbstractSinglet fission (SF), whereby a singlet exciton is converted into a pair of triplet excitons, can improve the efficiency of solar cells. Pentacene has been extensively studied as the most promising SF compound, owing to its 200% yield of triplet states. However, the easy degradation of pentacene in the presence of light and air owing to photooxidation cannot be explained by the classical 1O2 generation mechanism. To address this issue, in the present study, pentacene nanorods (Pc NRs) are prepared as a novel photosensitizer (PS); self‐carried Pc NRs exhibited higher 1O2 generation capacity. Thus, a novel 1O2 generation mechanism is proposed based on the SF effect. The initial photon absorption occurs to access single‐exciton states, S1–S3. Excited‐state Pc pairs accelerate the SF effect in pentacene NRs, leading to a non‐adiabatic transition to the dark D state. Dark D state is a singlet state by two triplets coupled overall, and it can transfer its energy to 3O2 for generating 1O2. Using Pc NRs as PSs, photodynamic therapy (PDT) inhibits tumor growth in 4T1 tumor‐bearing mice upon 405‐nm‐wavelength and 650‐nm‐wavelength laser irradiations. This study paves the way to discover novel PSs that are not considered with classical 1O2 generation mechanisms.

A biocompatible pure organic porous nanocage for enhanced photodynamic therapy.

Porphyrin-based photosensitizers have been widely utilized in photodynamic therapy (PDT), but they suffer from deteriorating fluorescence and reactive oxygen species (ROS) due to their close π-π stacking. Herein, a biocompatible pure organic porphyrin nanocage (Py-Cage) with enhanced both type I and type II ROS generation is reported for PDT. The porphyrin skeleton within the Py-Cage is spatially separated by four biphenyls to avoid the close π-π stacking within the nanocage. The Py-Cage showed a large cavity and high porosity with a Brunauer-Emmett-Teller surface area of over 300 m2 g-1, facilitating a close contact between the Py-Cage and oxygen, as well as the fast release of ROS to the surrounding microenvironment. The Py-Cage shows superb ROS generation performance over its precursors and commercial ones such as Chlorin E6 and Rose Bengal. Intriguingly, the cationic π-conjugated Py-Cage also shows promising type I ROS (superoxide and hydroxyl radicals) generation that is more promising for hypoxic tumor treatment. Both in vitro cell and in vivo animal experiments further confirm the excellent antitumor activity of the Py-Cage. As compared to conventional metal coordination approaches to improve PDT efficacy of porphyrin derivatives, the pure organic porous Py-Cage demonstrates excellent biocompatibility, which is further verified in both mice and rats. This work of an organic porous nanocage shall provide a new paradigm for the design of novel, biocompatible and effective photosensitizers for PDT.

Hyaluronic acid-targeted mixed micelles encapsulating hypericin for breast cancer photodynamic therapy

Hypericin (HYP) is an effective photosensitizer for photodynamic therapy (PDT). However, it has not been widely applied in clinical studies because of its low water solubility. In this study, hyaluronic acid-1,2-distearoyl-sn-glycero-3-phosphoethanolamine-polyethyleneglycol-2000 (HA-DSPE-PEG2000) and D-alpha-tocopheryl polyethylene glycol 1000 succinate (TPGS) were used to produce mixed micelles for the delivery of HYP (HA/HYP MM). The targeting ligand HA was conjugated to DSPE-PEG2000 as a novel biomaterial for the targeted drug delivery of HYP. The optimized HA/HYP MM exhibited excellent stability, biosecurity, and sustained drug release. Compared with free HYP and HYP MM, HA/HYP MM showed a stronger inhibitory effect against MCF-7 and MDA-MB-231 cells. No obvious toxicity was observed in normal breast cells. A cellular uptake study confirmed that HA could significantly increase intracellular HYP accumulation in tumor cells via the CD44 receptor. Further mechanistic studies showed that HA/HYP MM increased the intracellular reactive oxygen species (ROS) levels and induced cell death. HA/HYP MM may be an effective drug delivery system for breast cancer photodynamic therapy.

Substituted boron subphthalocyanines – Prospective compounds for theranostics: Synthesis, photochemical properties and in vitro cytotoxicity

Boron subphthalocyanines bearing a wide range of functional groups were tested as prospective photosensitizers and fluorophores. Synthetic protocols to novel 4-ethoxycarbonylphenoxy-substituted subphthalocyanine and phenoxy-substituted subphthalocyanine boron phenolate were presented. Differential triplet-triplet absorption spectra of subphthalocyanines were registered and triplet state lifetimes (τT = 0.6 ÷ 3.1 ms) were obtained. The results of flash photolysis measurements predicted the good ability of target subphthalocyanines to produce singlet oxygen and it was supported by the measurements of 1O2 quantum yields (ΦΔ = 0.47 ÷ 0.85). At the same time, satisfactory yields of fluorescence (Φf = 0.13 ÷ 0.50) were observed for most of the subphthalocyanines. The fluorescence decay kinetics were studied to determine the fluorescence lifetimes (τf = 0.30 ÷ 3.05 ns) and confirm the regularities obtained for fluorescence yields. Pronounced fluorescent properties allowed investigating the distribution of subphthalocyanines in the endoplasmic reticulum. In addition, the binding constants with human serum albumin were determined. tert-Butyl- and iodo-substituted subphthalocyanines demonstrated remarkable photocytotoxicity in human epidermoid carcinoma cells at micromolar concentrations. At the same time, target boron subphthalocyanines exhibited low dark cytotoxicity. All mentioned above make boron subphthalocyanines promising candidates as highly effective photosensitizers for photodynamic therapy and fluorescent labels for diagnostic.

Methylene Blue-Based Nano and Microparticles: Fabrication and Applications in Photodynamic Therapy.

Methylene blue (MB) has been used in the textile industry since it was first extracted by the German chemist Heinrich Caro. Its pharmacological properties have also been applied toward the treatment of certain diseases such as methemoglobinemia, ifosfamide-induced encephalopathy, and thyroid conditions requiring surgery. Recently, the utilization of MB as a safe photosensitizer in photodynamic therapy (PDT) has received attention. Recent findings demonstrate that photoactivated MB exhibits not only anticancer activity but also antibacterial activity both in vitro and in vivo. However, due to the hydrophilic nature of MB, it is difficult to create MB-embedded nano- or microparticles capable of increasing the clinical efficacy of the PDT. This review aims to summarize fabrication techniques for MB-embedded nano and microparticles and to provide both in vitro and in vivo examples of MB-mediated PDT, thereby offering a future perspective on improving this promising clinical treatment modality. We also address examples of MB-mediated PDT in both cancer and infection treatments. Both in-vitro and in-vivo studies are summarized here to document recent trends in utilizing MB as an effective photosensitizer in PDT. Lastly, we discuss how developing efficient MB-carrying nano- and microparticle platforms would be able to increase the benefits of PDT.

Porphyrin-lipid nanovesicles (Porphysomes) are effective photosensitizers for photodynamic therapy

Porphysomes (PS) are liposome-like nanoparticles comprising pyropheophorbide-conjugated phospholipids that have demonstrated potential as multimodal theranostic agents for applications that include phototherapies, targeted drug delivery and in vivo fluorescence, photoacoustic, magnetic resonance or positron emission imaging. Previous therapeutic applications focused primarily on photothermal therapy (PTT) and suggested that PSs require target-triggered activation for use as photodynamic therapy (PDT) sensitizers. Here, athymic nude mice bearing subcutaneous A549 human lung tumors were randomized into treatment and control groups: PS-PDT at various doses, PS-only and no treatment negative controls, as well as positive controls using the clinical photosensitizer Photofrin. Animals were followed for 30days post-treatment. PS-PDT at all doses demonstrated a significant tumor ablative effect, with the greatest effect seen with 10mg/kg PS at a drug-light interval of 24h. By comparison, negative controls (PS-only, Photofrin-only, and no treatment) showed uncontrolled tumor growth. PDT with Photofrin at 5mg/kg and PS at 10mg/kg demonstrated similar tumor growth suppression and complete tumor response rates (15 vs. 25%, p=0.52). Hence, porphysome nanoparticles are an effective PDT agent and have the additional advantages of multimodal diagnostic and therapeutic applications arising from their intrinsic structure. Porphysomes may also be the first single all-organic agent capable of concurrent PDT andPTT.

Photogeneration of Reactive Oxygen Species from Water-Soluble Phthalocyanine Derivatives Bound to a G-Quadruplex DNA

Abstract Water-soluble phthalocyanine (Pc) derivatives have been studied extensively as not only effective photosensitizers for photodynamic therapy (PDT), but also G-quadruplex ligands which have the potential to be anticancer drugs. We investigated the photogeneration of reactive oxygen species (ROS) from cationic Pc derivatives, 2,3,6,7,10,11,14,15-octakis-[N-methyl-(4-methylpyridinium-3-yloxy)phthalocyaninato] chloro gallium(III) iodide (GaPc) and zinc(II) iodide (ZnPc), in the presence of an all parallel-stranded tetrameric G-quadruplex DNA, i.e., [d(TTAGGGT)4]. We found that the photo ROS generation from GaPc is suppressed in the presence of the DNA, whereas that from ZnPc is enhanced on the addition of the DNA. The suppression of the photo ROS generation for GaPc by the DNA was found to be due to electron transfer from the ground state of the guanine base of the DNA to the photo-excited state of GaPc. This finding provides a clue as to why phototoxicity of GaPc is lower than that of ZnPc in human Hep2 cells (Fujishiro et al. J. Inorg. Biochem.2019, 192, 7). On the other hand, the enhancement of the photo ROS generation from ZnPc by the DNA is possibly due to the dissociation of its non-fluorescent aggregate through its interaction with the DNA. Thus the interaction of photosensitizers with DNA and RNA is crucial for their PDT efficacy.

Structural Modification Orientated Multifunctional AIE Fluorescence Probes: Organelles Imaging and Effective Photosensitizer for Photodynamic Therapy

AbstractLuminogens with aggregation‐induced emission feature (AIEgens) are highly demanded because of its excellent performance in fluorescent bioprobes. In this work, three AIEgens based on tetraphenylethylene isoquinolinium (TPE‐IQ) derivatives by introducing different electron donor and sterically hindered groups to replace the phenyl ring of the isoquinolinium core are prepared in a one‐pot reaction with a high yield and characterized systematically. By the analysis of photophysical properties and theoretical calculations, the structure‐property relationships among them become clear. Although they all inherit AIE feature as expected, these similar structural AIEgens present different organelle‐targets, which is attributed to their different cellular uptake way and energy barrier to cell membrane by detailed experiments. In addition, these TPE‐IQ‐based AIEgens are potential candidates for photodynamic therapy originating from their activities of generating reactive oxygen species under visible light irradiation.

Mitochondria-localized iridium(III) complexes with anthraquinone groups as effective photosensitizers for photodynamic therapy under hypoxia

Photodynamic therapy (PDT) is a potential way for the tumor treatment. However, it notably suffers the limitation of hypoxia in solid tumors. Thus, it is significant to develop effective photosensitizers which can exhibit excellent therapeutic performance under both normoxia and hypoxia. Herein, we reported four ionic iridium(III) complexes ( Ir1 – Ir4 ) with anthraquinone groups which can regulate their excited state energy levels effectively. Among them, the energy gap of Ir1 was between 1.63 and 2.21 eV, which can match well with that of O2, and the HOMO energy of Ir1 is less than −5.51 eV. Compared with Ir2 – Ir4 , the luminescent quantum efficiency of Ir1 was the highest. Particularly, Ir1 can specifically target the mitochondria of the tumor cells. Meanwhile, Ir1 showed high singlet oxygen quantum yields ( Φ Δ) in both solutions and living cells with low cytotoxicity. The results of PDT experiments revealed that Ir1 , as a photosensitizer, exhibited excellent therapeutic effect not only in normoxia but also in hypoxia condition. We believe that this work is meaningful for developing excellent PDT agents based on cyclometalated Ir(III) complexes via rational ligand modification.

Cover Feature: Highly Charged Ruthenium(II) Polypyridyl Complexes as Effective Photosensitizer in Photodynamic Therapy (Chem. Eur. J. 45/2019)

RuII polypyridyl complexes are promising candidates for application in the field of photodynamic therapy, thanks to their rich chemical physical repertoire. This work reports on two novel RuII and RuII/CuII mixed polypyridyl compounds which feature great cellular uptakes and can generate highly cytotoxic species when light-activated. The study highlights the key role of the Fenton active CuII center within the macrocycle residue of such compounds that would play a synergistic action with light activation in the formation of powerful Reactive Oxygen Species. More information can be found in the Full Paper by L. Conti, C. Giorgi, et al. on page 10606.

Highly Charged Ruthenium(II) Polypyridyl Complexes as Effective Photosensitizer in Photodynamic Therapy.

A comparative study between two novel, highly water soluble, ruthenium(II) polypyridyl complexes, [Ru(phen)2 L'] and [Ru(phen)2 Cu(II)L'] (L and L-CuII ), containing the polyaazamacrocyclic unit 4,4'-(2,5,8,11,14-pentaaza[15])-2,2'-bipyridilophane (L'), is herein reported. L and L-CuII interact with calf-thymus DNA and efficiently cleave DNA plasmid when light-activated. They also possess great penetration abilities and photo-induced biological activities, evaluated on an A375 human melanoma cell line, with L-CuII being the most effective. Our study highlights the key role of the Fenton active CuII center within the macrocycle framework, that would play a synergistic role with light activation in the formation of cytotoxic ROS species. Based on these results, an optimal design of RuII polypyridyl systems featuring specific CuII -chelating polyamine units could represent a suitable strategy for the development of novel and effective photosensitizers in photodynamic therapy.

In vitro and in vivo evaluation of a pyropheophorbide-a derivative as a potential photosensitizer for age-related macular degeneration

Abstract Photodynamic therapy (PDT) has been demonstrated to be an effective and safe treatment for subfoveal choroidal neovascularization (CNV) secondary to age-related macular degeneration (AMD). The photosensitizer is crucial factor in the efficacy of PDT. In this study, the physicochemical properties and the biological activity of a pyropheophorbide-a derivative, 2-(1-methoxyethyl)-2-devinylpyropheophorbide-a (MEP) had been evaluated in vivo and in vitro . MEP had a characteristic long wavelength absorption peak at 664 nm and the singlet oxygen quantum yield was determined as 0.38. In vitro , MEP showed low dark cytotoxicity and high photocytotoxicity, reducing the cell viability in a drug dose – dependent and light dose – dependent manner. In vivo , MEP could selectively localize to experimental CNV in BN rats, resulting in occlusion of CNV with minimal damage to retina tissues. The results indicate that MEP has the perspective to be developed as a safe and effective photosensitizer in PDT for AMD.

Triblock copolymers encapsulated poly (aryl benzyl ether) dendrimer zinc(II) phthalocyanine nanoparticles for enhancement in vitro photodynamic efficacy

A novel series of nanoparticles formed via an electrostatic interaction between the periphery of negatively charged 1–2 generation aryl benzyl ether dendrimer zinc (II) phthalocyanines and positively charged poly(L-lysin) segment of triblock copolymer, poly(L-lysin)-block-poly(ethylene glycol)-block-poly(L-lysin), was developed for the use as an effective photosensitizers in photodynamic therapy. The dynamic light scattering, atomic force microscopy showed that two nanoparticles has a relevant size of 80–150nm. The photophysical properties and singlet oxygen quantum yields of free dendrimer phthalocyanines and nanoparticles exhibited generation dependence. The intracellular uptake of dendrimer phthalocyanines in Hela cells was significantly elevated as they were incorporated into the micelles, but was inversely correlated with the generation of dendrimer phthalocyanines. The photocytotoxicity of dendrimer phthalocyanines incorporated into polymeric micelles was also increased. The presence of nanoparticles induced efficient cell death. Using a mitochondrial-sepcific dye rhodamine 123 (Rh123), our fluorescence microscopic result indicated that nanoparticles localized to the mitochondria.

Synthesis and antitumor activity evaluation of a novel porphyrin derivative for photodynamic therapy in vitro and in vivo.

A novel porphyrin derivative, 5, 10, 15, 20-tetrakis (5-morpholinopentyl)-21H, 23H-Porphin (MPP, 4) and its photophysical characteristics, therapeutic efficacy of photodynamic therapy (PDT) in vitro and in vivo, tumor selectivity, and clearance from normal tissues were investigated here. MPP has strong absorption at relatively long wavelength (λmax = 648nm, molar absorption coefficient ε ∼ 17,200M(-1)cm(-1)) and can emit strong fluorescence at 653 and 718nm. When administered to the animal tumor models by tail vein injection, MPP was capable of accumulating in the tumor site, as examined in vivo with the fluorescence signal of MPP. By the combination of MPP and a 650-nm laser irradiation, the viability of T24 cells could decrease by 4.37%, and inhibition rate of T24 tumor could increase up to 91.21% compared with control group, demonstrating the potential of MPP as an effective photosensitizer in PDT for tumor treatment.

DNA intercalating Ru(II) polypyridyl complexes as effective photosensitizers in photodynamic therapy.

Six substitutionally inert [Ru(II) (bipy)2 dppz](2+) derivatives (bipy=2,2'-bipyridine, dppz=dipyrido[3,2-a:2',3'-c]phenazine) bearing different functional groups on the dppz ligand [NH2 (1), OMe (2), OAc (3), OH (4), CH2 OH (5), CH2 Cl (6)] were synthesized and studied as potential photosensitizers (PSs) in photodynamic therapy (PDT). As also confirmed by DFT calculations, all complexes showed promising (1) O2 production quantum yields, well comparable with PSs available on the market. They can also efficiently intercalate into the DNA double helix, which is of high interest in view of DNA targeting. The cellular localization and uptake quantification of 1-6 were assessed by confocal microscopy and high-resolution continuum source atomic absorption spectrometry. Compound 1, and especially 2, showed very good uptake in cervical cancer cells (HeLa) with preferential nuclear accumulation. None of the compounds studied was found to be cytotoxic in the dark on both HeLa cells and, interestingly, on noncancerous MRC-5 cells (IC50 >100 μM). However, 1 and 2 showed very promising behavior with an increment of about 150 and 42 times, respectively, in their cytotoxicities upon light illumination at 420 nm in addition to a very good human plasma stability. As anticipated, the preferential nuclear accumulation of 1 and 2 and their very high DNA binding affinity resulted in very efficient DNA photocleavage, suggesting a DNA-based mode of phototoxic action.

Novel 3,6-bis(imidazolidine)acridines as effective photosensitizers for photodynamic therapy

The photoeffect of new proflavine derivatives with DNA-binding and antitumour activities, 3,6-bis((1-alkyl-5-oxo-imidazolidin-2-yliden)imino)acridine hydrochlorides (AcrDIMs), was studied to evaluate them as potential photosensitizers for photodynamic antitumor therapy. EPR measurements showed that superoxide radical anion and singlet oxygen were produced upon irradiation of AcrDIMs with UV-A light (>300nm) in the presence of molecular oxygen. This indicates that AcrDIMs may act as photosensitizers. The most active pentyl-AcrDIM and hexyl-AcrDIM displayed photocytotoxic effect toward the mouse lymphocytic leukemia cell line L1210 and human ovarian cancer cells A2780. Antitumor activity of pentyl-AcrDIM increased as high as about 12 times (72h incubation) after irradiation of A2780 cells (365nm, 1.05J/cm2). The photocytotoxicity seems to be associated with oxidative stress. Concerning the cell cycle, flow cytometry showed an arrest in the S-phase already 4h after irradiation. In a comet assay, no genotoxicity of AcrDIMs was found. Typical morphologic changes and formation of DNA-ladders indicated induction of apoptotic cell death, though no activation of caspase-3 was observed. Investigation of intracellular localization of pentyl-AcrDIM confirmed its partial accumulation in mitochondria and lysosomes. After irradiation of the A2780 cells, colocalization of pentyl-AcrDIM with monodansylcadaverine, a lysosomal dye, was proven, suggesting that lysosomes in the irradiated cells may be involved in the cell death.

Synthesis, spectroscopic properties and interaction with a liposomal membrane of a novel iodinated magnesium phthalocyanine

Abstract Phthalocyanines are applied as effective photosensitizers in photodynamic therapy of cancer and some other diseases. In this study, the synthesis of magnesium 2,9(10),16(17),23(24)-tetraiodophthalocyanine (2) is described. The spectroscopic, photophysical and photochemical parameters of phthalocyanine 2 are discussed, including the ability of this novel photosensitizer to generate singlet oxygen (1O2). The quantum yield of singlet oxygen formation (ΦΔ) was determined by two methods, viz. by measuring time-resolved phosphorescence at 1270 nm and by using 1,3-diphenylisobenzofuran and 9,10-dimethylanthracene, the well-known chemical acceptors. Applying the first method, the value of ΦΔ in N,N-dimethylformamide was found to be 0.70 ± 0.02, while using the second method the quantum yield of singlet oxygen formation was found to be 0.95 ± 0.01. This discrepancy lead to the conclusion that the photooxidation process with phthalocyanine 2 as the photosensitizer proceeds via a mixed mechanism, viz. Type II and Type I and/or Type III. The fluorescence quantum yield of 2 in N,N-dimethylformamide is 0.063 ± 0.004. The interaction between photosensitizer 2 and liposomes in an aqueous suspension was studied using a laser scanning confocal microscopy and the fluorescence technique. It was found that the binding constant of phthalocyanine 2 to liposomes was equal Kb = 40.5 ± 6.4 (mg/mL)−1. This implies, that the studied photosensitizer can readily penetrate cell or lipid membranes.