Zinc Naphthalocyanine Research Articles

Ultrafast Singlet−Singlet Energy Transfer in Self-Assembled via Metal−Ligand Axial Coordination of Free-Base Porphyrin−Zinc Phthalocyanine and Free-Base Porphyrin−Zinc Naphthalocyanine Dyads

Singlet-singlet energy transfer in self-assembled via axial coordination of imidazole-appended (at different positions of one of the meso-phenyl entities) free-base tetraphenylporphyrin, H(2)PIm, to either zinc phthalocyanine, ZnPc, or zinc naphthalocyanine, ZnNc, dyads is investigated in noncoordinating solvents, o-dichlorobenzene and toluene, using both steady-state and time-resolved transient absorption techniques. The newly formed supramolecular dyads were fully characterized by spectroscopic, computational, and electrochemical methods. The binding constants measured from optical absorption spectral data were found to be in the range of 10(4)-10(5) M(-1) for the 1:1 dyads, suggesting fairly stable complex formation. Electrochemical and computational studies suggested that photoinduced electron transfer is a thermodynamically unfavorable process when free-base porphyrin is excited in these dyads. Selective excitation of the donor free-base porphyrin entity was possible in both types of dyads formed by either of the ZnPc or ZnNc energy acceptors. Efficient singlet-singlet energy transfer was observed in these dyads, and the position of imidazole linkage on the free-base porphyrin entity, although flexible, seems to have some control over the overall efficiency of excited energy transfer process. Kinetics of energy transfer was monitored by performing transient absorption measurements using both up-conversion and pump-probe techniques. Such studies revealed ultrafast singlet-singlet energy transfer in the studied dyads with time constants on the order of 2-25 ps depending upon the type of the dyad.

Anomerically glycosylated zinc(II) naphthalocyanines

In course of our work on sugar-substituted phthalocyanines (Pc’s) for PDT applications, for the first time two macrocyclic Pc homologs, the anomerically tetraglucosylated Zn(II) naphthalocyanines 11 and 12 were synthesized and characterized.

Zinc phthalocyanine-nicotinamide complexes: evidence of their formation by using spectral studies

Spectral studies and job plot analyses which provide evidence of the formation of complexes of zinc phthalocyanines or zinc naphthalocyanines and nicotinamide or its positional isomers, known as isonicotinamide and picolinamide, are reported. Nicotinamide, isonicotinamide and picolinamide contain the amide group in a different position in the ring and these molecules can coordinate the metal of phthalocyanines through their nitrogen pyridinic atom, or their amide group, to form complexes. FT-IR and NMR spectroscopic studies, as well as job plot analyses in chloroform, have been performed. To validate the formation of complexes, some of them have been isolated, fully characterized and their binding properties and thermal stability have also been investigated.

Donor−Acceptor Nanohybrids of Zinc Naphthalocyanine or Zinc Porphyrin Noncovalently Linked to Single-Wall Carbon Nanotubes for Photoinduced Electron Transfer

The occurrence of photoinduced electron transfer in donor−acceptor self-assembled zinc naphthalocyanine (ZnNc) or zinc porphyrin (ZnP) single-wall carbon nanotube (SWNT) nanohybrids has been demonstrated. The nanohybrids were constructed by solubilizing carbon nanotubes by π−π stacking of pyrene functionalized to bear an imidazole moiety, ImPy-SWNT. Through the use of the imidazole ligand of the soluble ImPy-SWNT, donor ZnNc and ZnP entities were axially coordinated to yield ZnNc−ImPy-SWNT and ZnP−ImPy-SWNT donor−acceptor nanohybrids. The nanohybrids thus obtained were fully characterized by using transmission electron microscopy, UV−visible-near infrared spectroscopy, and electrochemical methods. Steady-state and time-resolved emission studies revealed efficient fluorescence quenching of the donor, ZnP, and ZnNc entities in the nanohybrids. Nanosecond transient absorption spectra revealed that the photoexcitation of the ZnNc or ZnP moiety resulted in the one-electron oxidation of the donor unit with a si...

Photophysical studies of supramolecular triads involving zinc naphthalocyanines and pyridylfullerenes with a second electron donor

Supramolecular triads composed of zinc naphthalocyanine ( ZnNc ) as an electron donor, pyridylfullerenes as primary electron acceptors, and either ferrocene ( Fc ) or N , N -dimethylaminophenyl ( DMA ) entities as second electron donors were constructed via metal-ligand axial coordination. The formation of the supramolecular triads was monitored using optical absorption methods and the measured binding constants revealed a moderately stable complex formation. The B3LYP/3-21G(*) optimized structures showed the disposition of the three entities of the triads to be in a linear fashion. The redox behavior of the different components was studied using cyclic voltammetry in o-dichlorobenzene containing (n- C 4 H 9)4 NClO 4. The donor ability evaluated from the oxidation potentials of the electron donors followed the trend: ZnNc < Fc < DMA . Efficient electron transfer from the excited singlet state of zinc naphthalocyanine to the fullerene entity was observed in all of the studied triads in o-dichlorobenzene by fluorescence quenching measurements. Clear evidence, that the charge-separation process formed the radical ions in the triads, was obtained from a nanosecond transient absorption spectral technique, indicating the contribution of the second electron donor in prolonging the charge-separated states.

A supramolecular Star Wars Tie Fighter Ship: electron transfer in a self-assembled triad composed of two zinc naphthalocyanines and a fullerene

Photoactive supramolecules composed of electron donor and electron acceptor entities are important for light energy harvesting applications. In the present study, a Star Wars Tie Fighter Ship shaped supramolecular triad was constructed by self-assembling two zinc naphthalocyanines to a fulleropyrrolidine bearing two pyridine entities using an axial coordination approach. Optical absorption and emission studies revealed stable complex formation, and the experimentally determined free-energy change revealed the possibility of electron transfer from singlet excited zinc naphthalocyanine to the fulleropyrrolidine. The picosecond time-resolved emission technique was utilized to evaluate the kinetics of charge separation while nanosecond transient absorption spectral studies provided evidence for electron transfer quenching. The measured charge-separation rate, k CS and quantum yield, Φ CS were found to be 5.7 × 109 s −1 and 0.93 in toluene, respectively, indicating an efficient process within the supramolecular triad. The charge recombination rate (k CR ) of the supramolecular ion-pair calculated from the nanosecond transient absorption technique was found to be 3.5 × 107 s −1 yielding a lifetime for the radical ion-pair (τ RIP ) of about 30 ns. Changing the solvent from the noncoordinating toluene to the coordinating benzonitrile or THF destroyed the supramolecular structure, and under these experimental conditions, only intermolecular electron transfer from the triplet excited zinc naphthalocyanine to fulleropyrrolidine could be observed. Under these conditions, the measured electron transfer rates, k et , T inter , were found to be 2.6 × 107 M −1. s −1 in benzonitrile and 1.2 × 107 M −1. s −1 in THF, respectively.

Photophysical and photochemical studies of zinc(ii) phthalocyanine derivatives—effects of substituents and solvents

The effects of substituents and solvents on the photophysical and photochemical parameters of zinc(II) phthalocyanines are reported. The complexes studied are zinc phthalocyanine (ZnPc), zinc tetra(tert-butylphenoxy)phthalocyanine [ZnPc(TBPh)4], zinc octa(methylphenoxy)phthalocyanine [ZnPc(MPh)8], zinc tetranitrophthalocyanine [ZnPc(NO2)4], zinc octachlorophthalocyanine (ZnPcCl8), zinc tetrasulfophthalocyanine [ZnPc(SO3−)4], a mixture of zinc mono-, di-, tri- and tetrasulfophthalocyanine [ZnPc(SO3−)mix] and zinc naphthalocyanine (ZnNPc). It was found that the presence of peripheral substituents on the macrocycle enhances the yield of the triplet state. Among the different substituents, the sulfonated derivative, ZnPc(SO3−)mix, has the longest triplet lifetime (τT) and the highest singlet oxygen quantum yield (ϕΔ). The near infra-red absorptions of the solvents reveal that solvents that absorb around 1100 nm (triplet energy level) and around 1270 nm (singlet oxygen energy level), quench the triplet state of the ZnPc derivative as well as singlet oxygen. Although water has a high singlet oxygen quenching effect, the ϕΔ value for ZnPc(SO3−)mix in water is still reasonably high at 0.48, which may provide an explanation for the efficient photosensitization by this molecule in photodynamic studies.

Influence of cyclodextrins on the fluorescence, photostability and singlet oxygen quantum yields of zinc phthalocyanine and naphthalocyanine complexes

The effects of formation of cyclodextrin inclusion complexes on the photochemical and photophysical properties of zinc phthalocyanine ( ZnPc ) and various peripherally substituted zinc phthalocyanines as well as zinc naphthalocyanine ( ZnNPc ) are investigated. The cyclodextrins employed were the hydroxypropyl-γ-cyclodextrin and unsubstituted β-cyclodextrin. Job's plots were employed to confirm the stoichiometry of the inclusion complexes and showed 2:1 and 4:1 (cyclodextrin:phthalocyanine) inclusion behavior. The phthalocyanine inclusion complexes showed larger singlet oxygen quantum yield (ϕΔ) values when compared to the free phthalocyanines before inclusion, for complexes 1 (zinc naphthalocyanine), 2 (zinc tetranitrophthalocyanine) and 4 (zinc tetra-tert-butylphenoxyphthalocyanine). The fluorescence quantum yields generally remained unchanged following inclusion.

Studies on intra-supramolecular and intermolecular electron-transfer processes between zinc naphthalocyanine and imidazole-appended fullerene.

Spectroscopic, computational, redox, and photochemical behavior of a self-assembled donor-acceptor dyad formed by axial coordination of zinc naphthalocyanine, ZnNc, and fulleropyrrolidine bearing an imidazole coordinating ligand (2-(4'-imidazolylphenyl)-fulleropyrrolidine, C60Im) was investigated in noncoordinating solvents, toluene and o-dichlorobenzene, and the results were compared to the intermolecular electron transfer processes in a coordinating solvent, benzonitrile. The optical absorption and ab initio B3 LYP/3-21G(*) computational studies revealed self-assembled supramolecular 1:1 dyad formation between the ZnNc and C60Im entities. In the optimized structure, the HOMO was found to be entirely located on the ZnNc entity while the LUMO was found to be entirely on the fullerene entity. Cyclic voltammetry studies of the dyad exhibited a total of seven one-electron redox processes in o-dichlorobenzene, with 0.1 M tetrabutylammonium perchlorate. The excited-state electron-transfer processes were monitored by both optical-emission and transient-absorption techniques. Direct evidence for the radical-ion-pair (C60Im.-:ZnNC.+) formation was obtained from picosecond transient-absorption spectral studies, which indicated charge separation from the singlet-excited ZnNc to the C60Im moiety. The calculated rates of charge separation and charge recombination were 1.4 x 10(10) s-1 and 5.3 x 10(7) s-1 in toluene and 8.9 x 10(9) s-1 and 9.2 x 10(7) s-1 in o-dichlorobenzene, respectively. In benzonitrile, intermolecular electron transfer from the excited triplet state of ZnNc to C60Im occurs and the second-order rate constant (kqtriplet) for this quenching process was 5.3 x 10(8)M-1s-1.

Electronic structure of reduced symmetry peripheral fused-ring-substituted phthalocyanines.

Reduced symmetry phthalocyanines are finding use in an increasing number of industrial applications. A detailed understanding of the electronic structure of the pi-system will greatly facilitate the design of new complexes, which fit the specifications required in many of these emerging high technology fields. NMR, electronic absorption, magnetic circular dichroism (MCD), and fluorescence emission and excitation spectra have been recorded for five generic metal phthalocyanine (MPc) derivatives in which additional benzene rings are fused either radially or obliquely onto at least one of the four peripheral benzo groups. The spectroscopy of four radially substituted compounds, zinc mononaphthotribenzotetraazaporphyrine (Zn3B1N), zinc monobenzotrinaphthotetraazaporphyrine (Zn1B3N), and two cis and trans zinc dibenzodinaphthotetraazaporphyrine (Zn2B2N) isomers, is compared to that of the obliquely fused structural isomer of Zn3B1N (Zn3BoN) and the D(4)(h)() symmetry parent compounds, ZnPc and zinc naphthalocyanine (ZnNc). The selection of Zn(II) as the central metal eliminates the possibility of charge transfer between the metal and ring. None of the complexes studied contain any sigma-bonded peripheral substituents. (1)H NMR signals of the seven compounds are assigned on the basis of the coupling patterns, integrated proton numbers, and decoupling experiments. The SIMPFIT program was used to perform spectral band deconvolution analyses of absorption and MCD spectra. ZINDO molecular orbital calculations are described, and the optical spectra are assigned on the basis of the MO models that have been developed previously to account for the spectral properties of metal porphyrin (MP(-2)) and metal phthalocyanine (MPc(-2)) complexes.

Synthesis of a Novel Asymmetrical Octasubstituted Zinc Naphthalocyanine

The synthesis and characterization of a novel asymmetrical octasubstituted zinc naphthalocyanine (ZnNc(OR1)6(OR2)2, R1=C4H9, R2=CH2CH2OCH3) made by mixed condensation are described.

Determination of quantum efficiency of persistent spectral hole burning using dispersive kinetics

A practical approach for the determination of the quantum efficiency of persistent spectral hole burning (PSHB) is suggested. The quantum efficiency is found from the experimental kinetics of hole formation. The method takes into account all primary mechanisms of dispersion for the hole burning kinetics and can be applied to the characterization and the comparison of materials with different mechanisms of hole burning. The quantum efficiency of PSHB has been found for free-base and zinc naphthalocyanines, which have photochemical and photophysical mechanisms of PSHB, respectively. These materials are useful for PSHB applications in the spectral range around 800 nm.

Comparative Photodynamic Therapy of B16 Pigmented Melanoma with Different Generations of Sensitizers

In order to apply photodynamic therapy to pigmented neoplasms, comparative photosensitizing studies of B 16 pigmented melanoma in C 57 B 1/6 mice were carried out with haematoporphyrin derivative (HpD), zinc(II) phthalocyanine ( ZnPc ), zinc(II) naphthalocyanine ( ZnNc ) and tetrabenzamido-substituted zinc(II) naphthalocyanine ( ZnNcA ). By injection of the optimal drug concentration and application of the optimal dose of light irradiation (the emission of the laser dye corresponding to the λmax value of the respective sensitizer) a phototherapeutic effect was observed only after photosensitization with the longest-wavelength-absorbing sensitizer, namely ZnNcA . It is supposed that the detected, through different assessment criteria, promising phototherapeutic effect after ZnNcA photosensitization of B 16 pigmented melanoma in mice is due to suitable structural, photophysical and photochemical properties of this sensitizer, but not due to a hyperthermic effect. This assumption is supported by the results obtained after irradiation of B 16 pigmented melanoma-bearing mice with the same fluence rate and fluence but without the sensitizer. In this case the tumour temperature did not increase by more than 35 °C and no changes in the mean tumour diameter or in the malignant subcellular components were detected.

Electrical conductivity and thermal diffusivity of zinc naphthalocyanine

Naphthalocyanine and its metal complexes are candidate materials for molecular electronic devices such as optical storage media, electrochromic displays and sensors [1,2]. Yanagi et al. [3] have investigated the molecular orientation of vacuum deposited zinc naphthalocyanine (ZnNc) by infrared (IR) spectroscopy, electronic spectroscopy and X-ray diffraction (XRD). Here we report the results of our study on the electrical conductivity and thermal diffusivity of ZnNc and iodine doped ZnNc. ZnNc was synthesized and purified by the method reported by Kaplan et al. [4]. The compound was characterized by elemental analysis, IR and electronic spectra. The data were in agreement with those reported in the literature [3]. ZnNc samples were doped with iodine in the solution phase by stirring 100 mg of powdered ZnNc with a saturated solution of iodine in carbon tetrachloride. The doped material was filtered and washed with carbon tetrachloride to remove excess iodine. This sample was dried at 360 K in vacuo as reported in the case of cobalt phthalocyanine [5]. The samples for measurement were formed into pellets of diameter 5.0 mm and thickness 1.1 mm at a pressure of 2000 kg cm -2. The electrical conductivity was measured in a shielded cell under dynamic vacuum in the temperature range 100-450 K using a Keithley model 617 electrometer. Thermal diffusivity of the pellets was measured by a photoacoustic technique, using 488 nm Ar ÷ laser beam at 26 mW power level. The laser beam was chopped using a Stanford Research System model SR 540 chopper, and front surface illumination was used for finding out the characteristic frequency f~. The schematic diagram of the experimental set up used for determination of the thermal diffusivity by the photoacoustic technique is shown in Fig. 1. The electrical conductivity of pristine ZnNc shows an increase in conductivity with temperature, the Arrhenius plots showing two linear regions of different activation energies, as shown in Fig. 2. The plot does not give any clear indication of a sharp transition. The activation energies in different temperature ranges are given in Table I. Doping with iodine enhances the electrical conductivity. For the iodine doped samples the Arrhenius plot gives two distinct regions with activation energies 0.05 eV and 0.14eV The enhanced electrical conductivity may be due to charge

A comparison of the photoproperties of zinc phthalocyanine and zinc naphthalocyanine tetrasulfonates: model sensitizers for the photodynamic therapy of tumors

Phthalo- and naphthaocyanines are of interest as sensitizers for the photodynamic therapy of tumors because of their strong absorption in the 680 and 760 nm ranges respectively. Both zinc phthalocyanine and naphthalocyanine tetrasulfonates (ZnPcS 4 and ZnNcS 4) were aggregated and photochemically inactive in aqueous buffer of pH 7.4, while in 10 mM cetyl pyridinium chloride in buffer they were monomeric and active. Therefore all these studies were carried out using the buffered detergent. The triplet lifetimes of ZnPcS 4 and ZnNcS 4 under argon were 490 and 110 μs respectively, with oxygen bimolecular quenching constants of 4.2 × 10 9 and 2.0 × 10 8 M −1s −1 respectively. Triplet decay curves in argon, air and 100% oxygen were first order, suggesting that there was little back reaction of the triplet states with oxygen as has been observed with some naphthalocyanines. The quantum yield of singlet oxygen generation by ZnPcS 4 was 0.70 and that for ZnNcS 4 was 0.25. Both compounds sensitized the photo-oxidation of furfuryl alcohol, cysteine, histidine, methionine, tryptophan, tyrosine and guanosine; ZnPcS 4 was three times more efficient than ZnNcS 4. These reactions were 50% inhibited by about 0.5 mM azide, suggesting the involvement of singlet oxygen. Both sensitizers photobleached on illumination, with quantum yields of 1.7 × 10 −5 for ZnPcS 4 and 4.2 × 10 −3 for ZnNcS 4.

Synthesis of Novel Soluble Poly(Aryl Ether)s Bearing Covalently Bound Naphthalocyanine Units

Abstract Thermally stable poly(aryl ether)s bearing covalently bound zinc(II) naphthalocyanine units have been synthesized by treatment of the dicyanoarylene-containing poly(aryl ether)s with excess amounts of naphthalocyanine molecules and zinc dust in bromonaphthalene. These polymers are soluble in common organic solvents. Their maximum absorption wavelength is 770 nm.

Electrochromic Oxidation and Reduction of Cobalt and Zinc Naphthalocyanine Thin Films

Electrochromism of cobalt and zinc naphthalocyanines (, ) was investigated in thin films vacuum‐deposited on indium tin oxide substrates. The film exhibited color changes from original green to purple both upon reduction and oxidation, and the film exhibited a color change from green to brown only upon oxidation. The electrochromic reduction was a reversible process depending on an electroactivity of the central Co metal, and the electrochromism was attributed to a transition from a reduced state related to the Co(I) center to a π*‐state of the Nc‐ligand. On the other hand, the electrochromic oxidation irreversibly occurred at the Nc‐ring ligand. The ring‐oxidation was stably maintained by a retention of incorporated anions, which caused a film restructuring accompanied with a discorder of molecular stacking from the original α‐polymorphic form to an amorphous structure in the oxidized state.

Liposome-delivered Zn(II)-2,3-naphthalocyanines as potential sensitizers for PDT: synthesis, photochemical, pharmacokinetic and phototherapeutic studies

The aim of this investigation is to report the synthesis and fundamental photochemical properties of naphthalocyanines with potential interest for photodynamic therapy (PDT), as well as their pharmacokinetics and phototherapeutic effects in a tumor model. Four zinc naphthalocyanines (ZnNc), unsubstituted ZnNc 1, tetraacetylamido-substituted ZnNc 2, tetraamino-substituted ZnNc 3 and tetramethoxy-substituted ZnNc 4 absorbing around 760–770 nm, were synthesized. The dye-sensitized photo-oxidation of 1,3-diphenylisobenzofuran via 1O 2 was studied in dimethylsulfoxide (DMSO). Quantum yields for this photoreaction are 0.135–0.164 and are relatively independent of the kind of substituent. In addition, the photoinduced electron transfer studied in N, N-dimethylformamide—water in the presence of methylviologen and mercaptoethanol is only slightly influenced by the kind of substituent. The pharmacokinetic properties of ZnNc 1 in hamsters bearing a transplanted rhabdomyosarcoma were studied using dipalmitoylphosphatidylcholine liposomes. Experimental PDT of rhabdomyosarcoma was carried out using liposome-delivered ZnNc 1–4. The phototherapeutic effect was evaluated by tumor photonecrosis, the mean tumor diameter during the observation period and the percentage of cured animals. The best effect was found after PDT with ZnNc 2 (50% of the treated animals were cured). A slightly lower effect was observed after application of ZnNc 4 (40% cured animals). No effect at all was noted after PDT with ZnNc 3 and a very low efficiency was found after treatment with ZnNc 1 as photosensitizer. Obviously, the photodynamic effect depends on the biological characteristics as well as on the nature of the substituents.

Photoreduction of methyl viologen sensitized by sulphonated phthalocyanines in micellar solutions

When sulphonated derivatives of zinc(II) phthalocyanine (ZnSP), palladium(II) phthalocyanine (PdSP) and zinc(II) naphthalocyanine (ZnSN) are incorporated into cationic micelles, these dyes can sensitize the reduction of methyl viologen (MV2+) by cysteine with red light (600–780 nm). The quantum yields for these reactions are low; 0.01 (PdSP), 0.001 (ZnSP) and 0.004 (ZnSN) mol ein–1. In the absence of micelles the dyes form photoinactive aggregates which do not sensitize the reduction of MV2+. Flash photolysis and fluorescence studies indicate that the reaction results primarily from reductive quenching of the phthalocyanine by cysteine, although in the case of ZnSN oxidative quenching of the triplet state by MV2+ also occurs.