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The kinetics of photobleaching of zinc(II) tetra-t-butyltetrabenzoporphyrin 1, zinc(II) 13,17-diethyl-12,18-dimethyl-5-azadibenzo[b,g]porphyrin 2 and zinc(II) tetra-t-butylphthalocyanine 3 are studied. In methanol containing ca 0.1% pyridine, complex 1 undergoes photoaggregation, 2 is relatively photostable, while 3 undergoes a smooth true photobleaching process with loss of intensity across the visible region. Where appropriate, apparent first-order rate constants for the photodiminution of the α band in the spectra are reported, and the effects of solvent variation and of additives are measured. It has not been possible to provide an overall rationalization of the solvent effects, but the effects of additives support the view that the photo-oxidative processes involve singlet oxygen. Experiments with potassium superoxide do not support superoxide involvement. Preparative experiments in methanol have been carried out with 1 and 3. 1 leads to a large recovery of the starting material, indicating that the photoaggregation does not involve the formation of new covalent bonds. 3 gives rise to at least five products (besides the starting material). Two of these, isolated in low yields (<5%), are identified as a fragmentation (depolymerization) product, 4-t-butylphthalonitrile, and the expected oxidative product, 4-t-butylphthalimide. The results are discussed and conclusions drawn.

In this work a selection of octasubstituted phthalocyaninato zinc complexes were synthesized and their photochemistry studied. The substituents included cholesterol (3a), estrone (3b), naphthol (3c) and phenoxy groups substituted with CH₃ (3d), C(CH₃)₃ (at two positions, 3e), C(CH₃)₃ (3f), NO₂ (3g), NH₂ (3h), COH (3i), COOH (3j), and H (3k). In general, complexes containing electron-donating groups attached to the phenoxy ring (e.g. 3e and 3f) were found to be photochemically unstable with photobleaching quantum yields of the order of 10^-3. In the presence of electron-withdrawing groups (3g, 3i, and 3j) the photobleaching quantum yields were of the order of 10^-6 to 10^-5. Singlet oxygen quantum yields (Φ_Δ) ranged from 0.01 to 0.73. The lowest Φ_Δ was observed for the highly aggregated complex 3c. All the complexes showed aggregation at high concentrations. Electrochemical reduction using a thin-layer spectroelectrochemistry cell showed that the complexes become more monomeric following reduction.

We present a new concept to adjust the transmission properties of a two-dimensional photonic crystal by photobleaching the structure. A square lattice of 500 nm lattice constant and 300 nm hole diameter was fabricated by etching air holes into a slab waveguide consisting of a polymethylmethacrylate polymer covalently functionalized with 10 mol% of the nonlinear Disperse Red 1 chromophore. While illuminating the photonic crystal with UV light the azo molecule bonds degenerate, resulting in a considerable refractive index change and a reduced slab waveguide core layer thickness. Wavelength and polarization dependent measurements show a very large shift of the dielectric band edge of 35 nm in TE and of 27 nm in TM polarization. With our novel concept it is possible to compensate fabrication inaccuracies and to trim photonic crystal transmission properties.

The organic salt 4-N, N-dimethylamino-4′-N′-methyl stilbazolium tosylate (DAST) is a nonlinear optical crystal with superior properties for integrated electro-optical applications and THz-devices. High quality DAST single crystals have been grown by the solution growth method. The electro-optical properties were determined in the spectral range between 700 and 1535 nm (r₁₁₁=47±8 pm/V at λ=1535 nm). Several planar structuring techniques for integrated optics applications based on DAST have been investigated. The production of single crystal thin films with minimal thicknesses of 10 μm is presented as well as the channel waveguide structuring of DAST surfaces by photobleaching techniques in the depth range of 0.2 up to 2.6 μm and by femtosecond laser ablation.

Adsorption and photocatalytic are commonly used methods for the removal of dye contained in industrial wastewater. Therefore, this study aimed to combine reduced Graphene Oxide (rGO) with Titanium Oxide (TiO₂) through various compositions using the hydrothermal method to obtain a catalyst of rGO/TiO₂ nanocomposites for the removal of contaminants from wastewater. The synthesized rGO/TiO₂ nanocomposites were mixed with methylene blue (MB) to reduce their content in water under dark conditions and UV light irradiation. The change of the optical properties of MB under both conditions was also examined, where a decrease in absorbance was observed. Under UV light irradiation, the maximum wavelength $({\lambda }_{max})$ of MB shifted from 664nm to 649nm but remained constant at 664nm in dark conditions. The results of optical characterizations confirmed that the adsorption of MB by rGO/TiO₂ nanocomposites under dark conditions did not change the MB structure. However, a significant degradation was observed with photocatalytic process under UV light irradiation. Nanocomposites rGO/TiO₂ with rGO 60% and TiO₂ 40% (GT40) have better performance in reducing MB under UV light irradiation.

Fulgide 1-E doped in polystyrene polymer films was heated at various annealing temperatures. Upon irradiation with UV light (366 nm), fulgide 1-E undergoes a conrotatory ring closure to the pink colored closed form 1-C. The later color was switched back to the original color when the films were irradiated with white light. The kinetics of photocoloration and photobleaching processes were followed spectrophotometrically by monitoring the absorbance of the ring closed product 1-C at its λ_max of 525 nm. The first-order plots of photocoloration reaction shows two distinct linear lines. The slopes of which corresponding to the first-order rate constants k₁ and k₂, where k₁ is the rate constant at initial reaction times and k₂ is that at late reaction times. These results suggest the plausible presence of two conformers of the ring opened form 1-E which reacts in sequence. On the other hand, photobleaching reaction shows a simple first-order reaction rate. It was found that for photocoloration reaction, the rate constant at initial reaction times is slower than that at late reaction times. Similarly, the photocoloration reaction is slower than the photobleaching reaction and both reactions increases with increasing the annealing temperatures. It was found that there was almost complete loss of photochemical fatigue resistance of fulgide 1 doped in polystyrene polymer film irrespective of the annealing temperature.

This work reports on the synthesis of tin and germanium phthalocyanine complexes containing phenoxy and substituted phenoxy groups as phthalocyanine ring substituents. The compounds studied are: dichlorogermanium phthalocyanine complexes containing eight phenoxy (4a), o-methyl phenoxy (4b) or estrone (4c) groups on the ring. The corresponding dichlorotin complexes (5a, 5b and 5c) and diiodotin complex (6a) were also investigated, as well as diestrone phthalocyaninato tin (7). Germanium octaphenoxy phthalocyanine complexes undergo phototransformation rather than direct photobleaching, whereas tin octaphenoxy phthalocyanine complexes undergo a photobleaching process, which is mediated by photoreduction of the phthalocyanine ring. Tin octaphenoxy phthalocyanine complexes gave higher Φ_Δ values than the corresponding germanium complexes. Also tin phthalocyanine complexes containing an unsubstituted ring gave higher Φ_Δ values than the corresponding octaphenoxy substituted complexes. The triplet quantum yields increased with the increase in electron-donating power of the ring substituents.

Binuclear ZnPc complexes covalently bridged by catechol units have been synthesized and their absorption and photochemical properties examined. The complexes studied are 1,2-bis-2',9',16',23'-triphenoxyphthalocyaninatozinc benzene (6a), 1,2-bis-2'-9',16',23'-tri-4-carboxyphe-noxyphthalocyaninatozinc benzene (6b), 1,2-bis-2',9',16',23'-tri-4-nitrophenoxyphthalocyaninato- zinc benzene (6c) and 1,2-bis-2'-9',16',23'-tri-4-tert-butylphenoxyphthalocyaninatozinc benzene (6d). Larger intramolecular coupling was observed for 6b and 6c, containing the carboxyphenoxy and nitrophenoxy substituents, respectively, than for 6a and 6d. A single Q band peak was observed for the fluorescence spectra of 6b and 6c, whereas, 6a and 6d showed a split Q band. The absence of the high energy fluorescence peaks corresponding to absorbance peaks in the 640 nm region, suggests that the intramolecular coupling is broken by excitation for complexes 6b and 6c.

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 (ϕ_Δ) 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.

Adjacent phthalocyanines with a binaphthalo backbone and phenoxy substituents were synthesized and their photochemical properties were investigated. The adjacent phthalocyanines are the binaphthalophthalocyanines, with the phenoxy, 4-tert-butylphenoxy and the sulfophenoxy substituents, respectively and bis-binaphthalophthalocyanine which has an extended π conjugation system and larger singlet oxygen quantum yield compared to the other compounds. The presence of the phenoxy substituents as well as the binaphthalo bridge does not cause a marked difference on the fluorescing properties of these complexes when compared to zinc phthalocyanine. The binaphthalo backbone allowed the molecules to photoswitch during photolysis affording them very high photostability.

The photophysical and photochemical properties and quenching (by 1,4-benzoquinone) of metallophthalocyanine sulfonates of aluminium (AlPcS_mix), zinc (ZnPcS_mix), silicon (SiPcS_mix), germanium (GePcS_mix) and tin (SnPcS_mix) are presented. The quantum yield values of fluorescence (Φ_F), triplet state (Φ_T), singlet oxygen (Φ_Δ) and photodegradation (Φ_d) were determined and the observed trends in their variation among the complexes discussed in terms of aggregation and the heavy atom effect. 1,4-benzoquinone effectively quenched the fluorescence of the complexes. Quenching analyses gave positive deviations from Stern-Volmer behavior, suggesting the existence of static quenching in addition to dynamic quenching. The static and dynamic components of the quenching were separated using a modified Stern-Volmer equation and the “sphere of action quenching model”. The quenching constant was found to be a function of the radius of the central metal ion.

Metallophthalocyanines form a very important class of commercial dyes and have achieved significant success in a variety of applications, in which their photostability is of fundamental importance. On this ground, considerable data on phthalocyanine photobleaching were published over recent years. We do not intend to give exhaustive compilation of the photobleaching quantum yields, which are known for wide circle of phthalocyanines in different solvents. This review begins by discussing pertinent background information about processes following phthalocyanine excitation. Then using selected examples of the recent literature, including authors' works, we survey a variety of photobleaching effects from the fundamental origins to specific for phthalocyanine chromophore. Finally, the mechanisms of phthalocyanine oxidative photobleaching are discussed.

The photochemical properties of water-insoluble metal-free tetraazachlorin derivatives in organic solvents and aqueous micellar solutions of nonionic surfactants were investigated. The quantum yields of fluorescence, singlet oxygen generation and photodegradation were evaluated in benzene. The highest photostability and singlet oxygen quantum yield (Φ_Δ = 0.7) was found for 2,2,3,3-tetramethyl-7,8,12,13,17,18-hexaphenyltetraazachlorin. The moderate Φ_Δ values (0.21–0.35) of triarenotetraazachlorins in benzene were established. Expansion of tetraazachlorin π-system by fusion of three aromatic rings leads to reduction of efficiency of singlet oxygen generation. The study of photodegradation mechanism shows that radical photooxidation apparently is most plausible, though ¹O₂ may partly contribute to photodestruction of some tetraazachlorins. In aqueous colloidal solution of nonionic surfactant (Cremophor EL) the same, as in benzene, effect of sensitizer structure upon efficacy of singlet oxygen production was observed. It was shown that ¹O₂ diffusion from micelle core into solution and then to target slows its oxidation rate substantially in comparison to the case where sensitizer and target are localized in the same micelle.

A series of magnesium, zinc and metal-free derivatives of non-peripherally substituted phthalocyanines (Pcs) bearing alkylsulfanyl or arylsulfanyl groups of different bulkiness was synthesized. Their spectral and photophysical properties including also the basicity of azomethine nitrogens and photostability were compared within the series as well as with similar peripherally substituted Pcs. Non-peripheral position of substituents led to the 70nm red-shift of Q-band in comparison to the peripherally substituted Pcs. However, unexpected blue-shift of approximately 50nm was observed in the series of non-peripherally substituted Pcs for the most bulky tert-butylsulfanyl derivative caused probably by extreme distortion of the macrocycle. The substitution had no effect on photophysical properties and compounds reached ${\mathrm{\Phi }}_{\mathrm{\Delta }}$ values 0.74–0.76 and ${\mathrm{\Phi }}_F$ 0.053–0.080 for zinc complexes, and ${\mathrm{\Phi }}_{\mathrm{\Delta }}$ 0.47–0.51 and ${\mathrm{\Phi }}_F$ 0.10–0.17 for magnesium complexes following the rule of heavy atom effect. Generally, non-peripherally substituted Pcs possessed improved singlet oxygen production in comparison to peripherally substituted ones. The photostability of the target compounds decreased with the red-shift of their absorption maxima with the arylsulfanyl derivatives being less photostable. The basicity of azomethine nitrogens was clearly dependent on the position and the character of substituent. Thus, non-peripherally substituted Pcs showed extraordinary increased basicity over the peripherally substituted ones with the most pronounced effect at alkylsulfanyl derivatives.

New class of clamshell-type lanthanide (Ce(IV), La(III) and Eu(III)) diphthalocyaninates bearing 24-crown-8 linking fragment are synthesized and characterized by means of NMR, UV-vis spectroscopies and MALDI-TOF mass spectrometry. A strong solvatochromism of the complexes, allowing switching the wide-range panchromatic absorption in polar solvents, is demonstrated by means of UV-vis and NMR spectroscopies and attributed to solvent-induced changing of sandwich conformations. The photodegradation of the obtained complexes was also investigated.

Aminolevulinic acid and hexyl-aminolevulinate serve as biological precursors to produce photosensitive porphyrins in cells via the heme biosynthetic pathway. This pathway is integral to porphyrin-based photodynamic diagnosis and therapy. By adding exogenous hexyl-aminolevulinate to rat bladder cancer cells (AY27, in vitro) and an animal bladder cancer model (in vivo), fluorescent endogenous porphyrin production was stimulated. Lipophilic protoporphyrin IX was identified as the dominant species by reverse high-pressure liquid chromatography. Subcellular porphyrin localization in the AY27 cells was evaluated by confocal laser scanning microscopy and showed almost quantitative bleaching after 20 s. From this study, we ascertained that the protocol described herein is suitable for hexyl-aminolevulinate-mediated photodynamic therapy and diagnosis when protoporphyrin IX is the active agent.

Aminolevulinic acid and hexyl-aminolevulinate serve as biological precursors to produce photosensitive porphyrins in cells via the heme biosynthetic pathway. This pathway is integral to porphyrin-based photodynamic diagnosis and therapy. By adding exogenous hexyl-aminolevulinate to rat bladder cancer cells (AY27, in vitro) and an animal bladder cancer model (in vivo), fluorescent endogenous porphyrin production was stimulated. Lipophilic protoporphyrin IX was identified as the dominant species by reverse high-pressure liquid chromatography. Subcellular porphyrin localization in the AY27 cells was evaluated by confocal laser scanning microscopy and showed almost quantitative bleaching after 20 s. From this study, we ascertained that the protocol described herein is suitable for hexyl-aminolevulinate-mediated photodynamic therapy and diagnosis when protoporphyrin IX is the active agent.