Spectroscopic studies of tin ethyl etiopurpurin in homogeneous and heterogeneous systems

Tin ethyl etiopurpurin is a promising second generation photosensitizer for photodynamic treatment of cancer. This compound is only poorly soluble in aqueous media and, therefore, needs a delivery system for administration to animals. Successful tumor eradication has previously been reported, following light exposure of rats previously administered with the purpurin formulated as a Cremophor El emulsion, in dipalmitoyl—phosphatidyl—choline liposomes or with gamma cyclodextrins. In this paper, we describe some absorbance and fluorescence studies of tin ethyl etiopurpurin in homogeneous and heterogeneous systems. In general, absorption and emission maxima were found to be red shifted as the environment changed from polar to non-polar. The viscosity and dielectric constant of the medium affected the purpurin fluorescence intensity. The liposome preparations were characterized by particle size determination, differential scanning calorimetry and by sensitizer fluorescence quenching studies. Photobleaching studies also showed variation owing to changes in the environment in which the dye was located.     

Segmented Frequency-domain Fluorescence Lifetime Measurements: Minimizing the Effects of Photobleaching Within a Multi-component System

This study introduces a newly developed frequency segmentation and recombination method for frequency-domain fluorescence lifetime measurements to address the effects of changing fractional contributions over time and minimize the effects of photobleaching within multi-component systems. Frequency segmentation and recombination experiments were evaluated using a two component system consisting of fluorescein and rhodamine B. Comparison of experimental data collected in traditional and segmented fashion with simulated data, generated using different changing fractional contributions, demonstrated the validity of the technique. Frequency segmentation and recombination was also applied to a more complex system consisting of pyrene with Suwannee River fulvic acid reference and was shown to improve recovered lifetimes and fractional intensity contributions. It was observed that photobleaching in both systems led to errors in recovered lifetimes which can complicate the interpretation of lifetime results. Results showed clear evidence that the frequency segmentation and recombination method reduced errors resulting from a changing fractional contribution in a multi-component system, and allowed photobleaching issues to be addressed by commercially available instrumentation. Electronic supplementary material The online version of this article doi: contains supplementary material, which is available to authorized users.     

Comparative photophysical and energy transfer studies of C480:C535 binary dye mixture in solid and liquid environments

The spectral behaviour of the individual dyes (C480 and C535) is discussed. The absorption and fluorescence spectral profiles of the dyes, in solid and liquid environments, are identical. Dye doped polymer rods of donor dye (C480) without the acceptor dye (C535), acceptor dye (C535) without the donor dye (C480) and donor dye with acceptor dye at different acceptor concentrations are synthesized. Energy transfer technique is studied, in detail, using these rods. The results obtained are compared with their respective liquid mixtures. Optical gain of the acceptor dye with and without the donor dye is determined experimentally, in both solid and liquid media. The gain of the acceptor with donor increases and then decreases with increase in acceptor concentration. Both solid and liquid media show similar trends. But, the gain coefficient in the solid matrix is less than that in the liquid medium. The photobleaching of the dye doped polymer rod under nitrogen laser excitation is studied.     

Photoexpansion and photobleaching effects in oxysulfide thin films of the GeS2+Ga2O3 system

Oxysulfide systems undergo structural transformations upon illumination with laser light of near bandgap energy, as well as chalcogenide materials (glasses and films). In this paper, photoinduced effects such as photoexpansion and photobleaching were observed in GeS₂+Ga₂O₃ (GGSO) films synthesized by electron beam evaporation. A surface expansion of the thin films and a shift to shorter wavelengths of the optical absorption edge were observed as a result of UV laser irradiation (wavelength of 351 nm) and they are dependent on laser power density, exposure time and film composition. These parameters were varied to evaluate and enhance the observed effects. In addition, the irradiated GGSO samples exhibited a decrease in refractive index, measured with a prism-coupling technique, which makes these films suitable candidates for applications as gratings and waveguides in integrated optics.     

聚合物PMMA/DR1啁啾光栅耦合器的研究

从理论上分析出在一定条件下啁啾光栅输出耦合器具有较好的聚焦衍射光束的作用.实验上采用光漂白方法,利用两束激光在PMMA/DR1平面波导上所形成的干涉条纹来制备啁啾光栅,研究了这种啁啾光栅耦合器衍射光的聚焦效应,观测结果与理论分析基本相符.     

Photobleaching as a useful technique in reducing of fluorescence in Raman spectra of blue automobile paint samples

The usefulness of the photo-beaching technique in reducing the fluorescence background in Raman spectra of automotive paints was studied. The method was applied to group of 20 blue solid and metallic paints, in which pigment identification with the use of a green laser (514.5 nm) was not possible due to strong fluorescence. The samples were irradiated by high laser power for a long period of time before acquiring spectra. The process of bleaching was studied in detail based on two samples. Then the procedure was applied to all samples before acquiring spectra. Due to irradiation fluorescence originating from the background decreased, whereas Raman scattering features of samples stayed unchanged. The applied procedure satisfactorily quenched fluorescence in 90% of examined samples and made pigment identification possible.     

Effect of aggregation state, temperature and phospholipids on photobleaching of photosynthetic pigments in spinach Photosystem II core complexes

Photosystem II (PSII) complex activity is known to decrease under strong white light illumination, and this photoinhibition phenomenon is connected to the photobleaching of the PSII photosynthetic pigments. In this work the pigment photobleaching has been studied on PSII core complexes, by observing the effects of different factors such as the aggregation state (PSII monomers and dimers were used), temperature (20 degrees C and 10 degrees C temperatures were tested) and the presence of the exogenous phospholipids (cardiolipin and phosphatidylglycerol). In particular, PSII resistance against white light stress was studied by means of UV/VIS Absorption and Fluorescence Emission measurements. It was found that PSII dimers resulted more resistant against photobleaching and that lower temperature reduces the pigment photodestruction. Moreover, the presence of phosphatidylglycerol or cardiolipin enhanced the PSII resistance to the photobleaching phenomenon, mainly at lower temperatures.     

荧光光谱用于光动力疗法中光敏剂光漂白特性研究

应用荧光光谱技术研究溶液中血卟啉单甲醚(HMME)的光漂白与光产物生成。以532 nm倍频Nd∶YAG激光器照射样品,功率密度为100 mW·cm-2,以光学多通道分析仪(OMA)采集荧光光谱。照光过程与荧光光谱采集同步进行。通过构建基本光谱与最小二乘拟合,由单条实测光谱中分解求得HMME荧光(613 nm)、光产物荧光(639 nm)及自体荧光的强度。HMME初始浓度不超过10 μg·mL-1时符合荧光-浓度线性函数关系。对照光过程的荧光光谱监测同时观察到HMME漂白、光产物生成与漂白,以及样品光学特性变化引起的自体荧光强度起伏。光产物漂白后的二次产物引起样品光学特性显著改变。所建立的荧光光谱探测系统与光谱分析方法可满足光敏剂漂白特性体外研究的需要,并为光动力治疗的剂量学在体监测提供有效研究方法。     

Photochemical studies of tetra-2,3-pyridinoporphyrazines

Tetra-2,3-pyridinoporphyrazines and the corresponding water-soluble N,N′,N′′,N′′′-tetramethyl-tetra-2,3-pyridinoporphyrazine complexes, containing central metal atoms; M=Ge, Sn, Si and Zn, were synthesized and their photochemical properties were investigated. The reductive quenching of pyridinoporphyrazines excited states, enhanced relative to phthalocyanines, was considered as the first photochemical step of dyes phototransformation in dimethylformamide (DMF) and dimethylsulfoxide (DMSO) solutions under irradiation with visible light. Efficiency of singlet oxygen photosensitization decreases significantly in the row phthalocyanines, unquaternized, quaternized tetra-2,3-pyridinoporphyrazine metallocomplexes.