Changes In Quantum Yield Research Articles

Spectral Characteristics of Water-Soluble Rhodamine Derivatives for Laser-Induced Fluorescence.

We present a comprehensive fluorescence characterization of seven water-soluble rhodamine derivatives for applications in laser-induced fluorescence (LIF)techniques. Absorption and emission spectra for these dyes are presented over the visible spectrum of wavelengths (400 to 700nm). Their fluorescence properties were also investigated as a function of temperature for LIF thermometry applications. Rhodamine 110 depicted the least fluorescence emission sensitivity to temperature at -0.11%/°C, while rhodamine B depicted the most with a -1.55%/°C. We found that the absorption spectra of these molecules are independent of temperature, supporting the notion that the temperature sensitivity of their emission only comes from changes in quantum yield with temperature. Conversely, these rhodamine fluorophores showed no change in emission intensities with pH variations and are, therefore, not suitable tracers for pH measurements. Similarly, fluorescent lifetime, which is also a property sensitive to local environmental changes in temperature, pH, and ion concentration, measurements were conducted for these fluorophores. It was found that rhodamine B and kiton red 620 have shorter fluorescence timescales compared to those of the other five rhodamine dyes, making them least suitable for applications where temporal changes in emission are monitored. Lastly, we conducted experiments to assess the physicochemical absorption characteristics of these dyes' molecules into polydimethylsiloxane (PDMS), the most common material for microfluidic devices. Rhodamine B showed the highest diffusion into PDMS substrates as compared to the other derivative dyes.

Photophysical properties of Radachlorin photosensitizer in solutions of different pH, viscosity and polarity

We present a thorough experimental investigation of fluorescence properties of Radachlorin photosensitizer in solutions of different acidity, viscosity and polarity. Experiments were performed using time-resolved fluorescence lifetime imaging and time-resolved analysis of polarized fluorescence. Variations of solution acidity resulted in considerable changes of Radachlorin fluorescence quantum yield and lifetime in the pH range from 4 to 7, but did not affect the rotational diffusion time, and almost did not change the quantum yield and characteristic times of singlet oxygen phosphorescence. Variations of solution polarity and viscosity were achieved by changing ethanol or methanol fraction in aqueous solution. The decrease of solution polarity resulted in nonlinear rise of Radachlorin fluorescence quantum yield and lifetime up to alcohol concentration of 50%–65%, as well as in considerable rise of singlet oxygen quantum yield and significant changes in characteristic times of its phosphorescence. Variations of solution viscosity resulted in changes of rotational diffusion time of Radachlorin molecules, which appeared to be in perfect correlation with methanol solution viscosity. Good correspondence with ethanol solution viscosity was observed only up to 50% alcohol fraction. Deviations of rotational diffusion time of Radachlorin molecules from direct proportionality with solution viscosity at higher ethanol concentrations were suggested to be due to different solvation conditions. The data obtained can give important reference points for analysis of microenvironment of Radachlorin molecules, their intracellular localization and performance in singlet oxygen generation.

Novel salicylic acid derivatives connecting to five-membered cycle through an acyl hydrazone bond as multi-stimuli responsive fluorescent smart materials with photoswitching properties

In order to exploit novel multi-stimuli responsive fluorescent materials, a series of novel fluorescent molecules of salicylic acid derivatives were designed and synthesized via introducing pyrazole or cyclopentane to the salicylic acid scaffold through a special Schiff base–acylhydrazone, and the molecular structures of representative compounds A2 and A4 were verified via single crystal X–ray diffraction. All title molecules could exhibit obvious solvatofluorochromism from cyan to indigo in several solutions with different polarity. The fluorescence titration data exhibited compound A2 and complex A2-Cu2+ with prime detection limits to Cu2+ (0.24 μM) and S2- ions (2.83 μM). The sensitive recognition of A2 to trifluoroacetic (TFA) and A2-TFA to triethylamine (TEA) were also confirmed via fluorescent titration experiments in various solutions, respectively. What’s more, the 1H NMR and UV/Vis absorption spectra further explained the mechanism between molecules and ions or molecules and TFA/TEA. Besides, the photoswitching properties of the compounds A2 and A3 could be demonstrated via the irradiation of special wavelength light or heating accompanied with changes in quantum yields. In addition, these phenomena of multiple responses were explained via Density Functional Theory (DFT) based on the Gaussian calculations. Thus, this work provided a preliminary basis for the research of multi-stimuli responsive fluorescent molecules with photoswitching properties.

Four new Zn(II) complexes based on 2-thienoyltrifluoroacetone and N-donor auxiliary bridging and chelating ligands: Synthesis, spectroscopic and structural studies, thermal behavior and Hirshfeld surface analysis

Two new mononuclear complexes,[Zn(2,2′-bpy)(ttfa)2] (1), [Zn(1,10-phen)(ttfa)2] (2) and two one dimensional coordination polymers, [Zn(bpp)(ttfa)2]n (3) and [Zn(bpe)(ttfa)2]n (4) (Httfa = 2-thenoyltrifluoroacetone, 2,2ʹ-bpy = 2,2ʹ-bipyridine, 1,10-phen = 1,10-phenanthroline, bpp = 1,3-bis(4-pyridyl)propane and bpe = 1,3-bis(4-pyridyl)ethane), have been synthesized. They were fully characterized by single-crystal X-ray diffraction, elemental analyses, FT-IR and 1H NMR spectroscopy and thermogravimetry. The zinc atoms show distorted octahedral coordination geometries. In addition to evaluate the thermal behavior of the compounds, the 3D Hirshfeld surface analysis and 2D fingerprint maps were used for quantitative mapping of the intermolecular interactions. The emission characteristics of Zinc(II) complexes are influenced by the ligands present, which in turn affect the environment of the Zinc(II) ion. This tuning leads to changes in photoluminescence (PL), absorption (Abs) spectra and quantum yield.

Landscape gradient of autumn photosynthetic decline in Abies sachalinensis seedlings

Understanding what environmental factors are genetically linked to a phenological event is critical for predicting responses to climate change. Photosynthetic phenology often varies among a species of evergreen conifers due to local adaptation. However, few empirical studies have revealed relevant relationships between climatic factors in provenance environments and photosynthetic phenology. This study evaluated the effects of environmental conditions of the growing site and seed source provenance on the seasonal changes in maximal photochemical quantum yield of photosystem II (Fv/Fm) in a common garden experiment with 2-year-old seedlings of Sakhalin fir (Abies sachalinensis), a representative species with local adaptation, from four seed source provenances. A logistic model was constructed to explain the seasonal variation of Fv/Fm from July to October and the relationships between the estimated model parameters and representative factors featuring provenance environments were evaluated. The landscape gradient of the detected model parameters responsible for the provenance environments was visualized in a map of the distribution area. The lowest temperature was the most plausible factor in the growing environment to explain the seasonal changes of Fv/Fm. Among the representative meteorological factors of provenance environments, the lowest temperatures in July showed significant relationships with two model parameters, explaining the lower limit of Fv/Fm and the higher sensitivity of autumn Fv/Fm decline. The estimated spatial maps of model parameters consistently showed that the higher the lowest temperature in July in the provenance environment, the lower the Fv/Fm in October and the greater the decrease in the autumn Fv/Fm decline. Therefore, the lowest summer temperature could be associated with the local adaptation of autumn photosynthetic phenology in A. sachalinensis.

Orthogonally-tunable and ER-targeting fluorophores detect avian influenza virus early infection

Cell-based assays can monitor virus infection at a single-cell level with high sensitivity and cost-efficiency. For this purpose, it is crucial to develop molecular probes that respond selectively to physiological changes in live cells. We report stimuli-responsive light-emitters built on a T-shaped benzimidazole platform, and consecutive borylation reactions to produce a library of homologs displaying systematic changes in fluorescence quantum yield and environmental sensitivity. We find that certain fluorophores localize selectively at the endoplasmic reticulum, and interact with proteins involved in the stress signaling pathways. Notably, the mono-borylated compound responds selectively to the stress conditions by enhancing fluorescence, and detects avian influenza virus infection at the single-cell level. Our findings demonstrate the unprecedented practical utility of the stress-responsive molecular probes to differentiate cellular states for early diagnosis.

Bridging the gap between H- and J-aggregates: Classification and supramolecular tunability for excitonic band structures in two-dimensional molecular aggregates

Molecular aggregates with long-range excitonic couplings have drastically different photophysical properties compared to their monomer counterparts. From Kasha's model for one-dimensional systems, positive or negative excitonic couplings lead to blue or red-shifted optical spectra with respect to the monomers, labeled H-and J-aggregates, respectively. The overall excitonic couplings in higher dimensional systems are much more complicated and cannot be simply classified from their spectral shifts alone. Here, we provide a unified classification for extended 2D aggregates using temperature dependent peak shifts, thermal broadening, and quantum yields. We discuss the examples of six 2D aggregates with J-like absorption spectra but quite drastic changes in quantum yields and superradiance. We find the origin of the differences is, in fact, a different excitonic band structure where the bright state is lower energy than the monomer but still away from the band edge. We call this an “I-aggregate.” Our results provide a description of the complex excitonic behaviors that cannot be explained solely on Kasha's model. Furthermore, such properties can be tuned with the packing geometries within the aggregates providing supramolecular pathways for controlling them. This will allow for precise optimizations of aggregate properties in their applications across the areas of optoelectronics, photonics, excitonic energy transfer, and shortwave infrared technologies.

Kinetics of Plant‐derived Heteropolysaccharide Bioabsorption Characterized by Fluorescence‐based Microfluidics System

Plant‐derived structural polymer, pectin, is the “glue” between plant cells, a biomaterial with promising performance as a sealant on visceral organs. However, the nature of bioabsorption and biodurability of pectin remains unclear. Here, we investigate the feasibility of a quantitative microfluidic perfusion assay based on photochemical quenching, to define the kinetics of pectin bioabsorption.We hypothesize that fluorescent tracers embedded into pectin biopolymers will reliably reflect predictable kinetics patterns of bioabsorption including predictable trends when modifying the chemical species used in fluorescence quenching experiments.A fluorescent tracer, Fluorescein Sodium, was embedded into high methoxyl citrus pectin. Dried Fluorescein pectin films were placed into 24‐well plates, to monitor degradation via parallel microfluidics perfusion. This perfusion was performed via micro‐perfused exogenous 0.4% Trypan Blue, an anionic hydrophilic azo dye, which was delivered into porous matrix interfacing on pectin in each well. To assess biodurability, the fluorescence of perfused pectin under quenching by dye was monitored over time using a multi‐well plate fluorescence reader (Cytofluor 4000, PerSeptive Biosystems).Our data show that consistent trends in fluorescence result during quenching experiments. When un‐perfused, Fluorescein‐embedded pectin exhibited statistically insignificant change in quantum yield over 1 week (p=0.457), suggesting that results were not impacted by substantial photobleaching over the course of experimentation. To minimize interfacial flow artifact, 6µm porous matrix provided an effective interface for observable perfusion of azo dye into pectin. During micro‐perfusion, serial measurements of fluorescence in Fluorescein pectin demonstrated exponential decline in fluorescence intensity. This quenching of fluorescent signal from Fluorescein correlated with the progressive bioabsorption of the pectin polymer. Absorption was feasibly modulated by adjusting dye volumes used in perfusion.In this in vitro assay, plant‐derived pectin exhibits predictable decay characteristics and bioabsorption kinetics when incorporated with fluorescent tracers. These tracers not only provide a quantitative measure of biodurability, but also an opportunity for guided biochemical tuning of the complex biomaterial, to improve its performance as a potential therapeutic sealant.

A Multicenter Metal–Organic Framework for Quantitative Detection of Multicomponent Organic Mixtures

A Multicenter Metal–Organic Framework for Quantitative Detection of Multicomponent Organic Mixtures

Blue and green light exciton emission of chloro-brominated perovskite quantum dots glasses

Blue and green light emitting CsPbBr3 and CsPb(Cl/Br)3 perovskite quantum dots glasses (QDGs) have been fabricated in multi-component borate glass matrices by melt quenching method and following heat treatment. Absorption spectra show regular blue shift of first exciton absorption peak from CsPbBr3 to CsPb(Cl/Br)3 QDGs. Photoluminescence spectra show that CsPbBr3 and CsPb(Cl/Br)3 QDGs have adjustable emission in the wavelengths from 528 to 442 nm. The full width at half maximum (FWHM) is 15–17 nm and 21–31 nm for CsPbBr3 and CsPb(Cl/Br)3 QDGs respectively. Emission map and photoluminescence excitation spectra show broad band excitation characteristics of the exciton emission. Photoluminescence decay shows bi-exponential function for both CsPbBr3 and CsPb(Cl/Br)3 QDGs. As the ratio of Cl/Br increases from CsPbBr3 to CsPb(Cl/Br)3 QDGs, the short and long lifetime components roughly decrease from 9.7 to 4.0 ns and from 87.8 to 55.2 ns respectively, and the average lifetime decreases from 72.2 to 36.5 ns. Photoluminescence quantum yield changes from 82.8% to 5.7%. Temperature dependence of PL spectra in the range of 28–120 °C shows that integrated intensity obviously decreases with increasing temperature, but the emission peak wavelength and FWHM almost do not change.

In Situ Optical Studies on Morphology Formation in Organic Photovoltaic Blends

The efficiency of bulk heterojunction (BHJ) based organic solar cells is highly dependent on the morphology of the blend film, which is a result of a fine interplay between donor, acceptor, and solvent during the film drying. In this work, a versatile set-up of in situ spectroscopies is used to follow the morphology evolution during blade coating of three iconic BHJ systems, including polymer:fullerene, polymer:nonfullerene small molecule, and polymer:polymer. the drying and photoluminescence quenching dynamics are systematically study during the film formation of both pristine and BHJ films, which indicate that the component with higher molecular weight dominates the blend film formation and the final morphology. Furthermore, Time-resolved photoluminescence, which is employed for the first time as an in situ method for such drying studies, allows to quantitatively determine the extent of dynamic and static quenching, as well as the relative change of quantum yield during film formation. This work contributes to a fundamental understanding of microstructure formation during the processing of different blend films. The presented setup is considered to be an important tool for the future development of blend inks for solution-cast organic or hybrid electronics.

Investigation on Photoluminescence of CsPb(Br,I)3 Perovskite Nanocrystals by Comparison between Hot-Injection and Ion-Exchange Methods

Changes in photoluminescence (PL) peak width and quantum yield (PLQY) with halide composition were compared for CsPb(Br1−x I x )3 nanocrystals (NCs) prepared by hot-injection and ion-exchange methods. The hot-injection method produced single-phase cubic CsPb(Br1−x I x )3 NCs for each iodide ratio. In contrast, a small amount of orthorhombic phase was observed at higher x for NCs prepared by the ion-exchange methods. The PL peak width of mixed-halide NCs at x = 0.55 was broader than those of CsPbBr3 and CsPbI3, possibly as a result of compositional inhomogeneity among the individual NCs. However, the maximum PL peak width occurred at larger x for the ion-exchange methods, possibly because of partial transition to orthorhombic phase from cubic phase for CsPb(Br1−x I x )3 NCs. The minimum PLQY for the hot-injection method was 25.0% at x = 0.50, which was lower than the PLQYs of CsPbBr3 and CsPbI3 NCs (∼70%). In contrast, the minimum PLQY for the ion-exchange methods occurred at x = ∼0.3. Furthermore, the minimum PLQY was ∼10%, which was lower than 25.0% for the hot-injection method. The addition of halide solution for ion exchange might affect the adsorption state of surface modifiers, leading to the decreased PLQY.

Spectral and time-resolved photoluminescence of human platelets doped with platinum nanoparticles.

This paper describes a detailed study of spectral and time-resolved photoprocesses in human platelets and their complexes with platinum (Pt) nanoparticles (NPs). Fluorescence, quantum yield, and platelet amino acid lifetime changes in the presence and without femtosecond ablated platinum NPs have been studied. Fluorescence spectroscopy analysis of main fluorescent amino acids and their residues (tyrosine (Tyr), tryptophan (Trp), and phenylalanine (Phe)) belonging to the platelet membrane have been performed. The possibility of energy transfer between Pt NPs and the platelet membrane has been revealed. Förster Resonance Energy Transfer (FRET) model was used to perform the quantitative evaluation of energy transfer parameters. The prospects of Pt NPs usage deals with quenching-based sensing for pathology’s based on platelet conformations as cardiovascular diseases have been demonstrated.

Dithiane Based Boronic Acid as a Carbohydrate Sensor in an Aqueous Solution at pH 7.5: Theoretical and Experimental Approach.

Carbohydrate sensing in an aqueous solution remains a very challenging area of interest. Using the idea of covalent reversible interaction between boronic acids and the diol groups in carbohydrates enable us to design a carbohydrate sensor 1-thianthrenylboronic acid (1T), which has high selectivity towards fructose. To elucidate the sensing and binding properties of 1T with sugars, we have incorporated theoretical (DFT and TD-DFT) and spectroscopic techniques. For an optimized geometry, the complete vibrational assignments were done with FT-IR and FT-Raman spectra. Physiochemical parameters were obtained by implementing frontier molecular orbital (FMO) analysis. Further, excited state properties were determined by performing TD-DFT calculations in solvent and these properties were in good agreement with the experiment. The steady state fluorescence measurements with varying concentration of sugars, revealed that the fluorescence intensity of boronic acid is enhanced by studied sugars due to the structural modification. We also noticed remarkable changes in fluorescence lifetimes and quantum yield after adding sugars. The article also reports influence of pH on boronic acid's fluorescence intensity with and without sugars. The fluorescence of boronic acid increases with the increase in pH. These changes are due to acid-base equilibrium of boronic acid and led us to estimate the pKa value of 7.6. All the theoretical and experimental evidences suggested that 1T can be used as a possible fluorescent sensor for fructose. In addition, 1T showed very good affinity for Cu2+ ion with Ka = 150 × 102M-1, which suggests that 1T can also be used as a chemosensor for Cu2+ ions.

Ruthenium-Benzothiadiazole Building Block Derived Dynamic Heterometallic Ru-Ag Coordination Polymer and Its Enhanced Water-Splitting Feature.

This article deals with the development of the unprecedented redox-mediated heterometallic coordination polymer {[RuIII(acac)2(μ-bis-η1-N,η1-N-BTD)2AgI(ClO4)]ClO4}n (3) via the oxidation of the monomeric building block cis-[RuII(acac)2(η1-N-BTD)2] (1) by AgClO4 (BTD = exodentate 2,1,3-benzothiadiazole, acac = acetylacetonate). Monomeric cis-[RuII(acac)2(η1-N-BTD)2] (1) and [RuII(acac)2(η1-N-BTD)(CH3CN)] (2) were simultaneously obtained from the electron-deficient BTD heterocycle and the electron-rich metal precursor RuII(acac)2(CH3CN)2 in refluxing CH3CN. Molecular identities of 1-3 were authenticated by their single-crystal X-ray structures as well as by solution spectral features. These results also reflected the elusive trigonal-planar geometry of the Ag ion in Ru-Ag-derived polymeric 3. Ru(III) (S = 1/2)-derived 3 displayed metal-based anisotropic EPR with ⟨g⟩/Δg = 2.12/0.56 and paramagnetically shifted 1H NMR. Spectroelectrochemistry in combination with DFT/TD-DFT calculations of 1n and 2n (n = 1+, 0, 1-) determined a metal-based (RuII/RuIII) oxidation and BTD-based reduction (BTD/BTD•-). The drastic decrease in the emission intensity and quantum yield but insignificant change in the lifetime of 3 with respect to 1 could be addressed in terms of static quenching and/or a paramagnetism-induced phenomenon. A homogeneously dispersed dumbbell-shaped morphology and the particle diameter of 3 were established by microscopic (TEM-EDX/SEM) and DLS analysis, respectively. Moreover, the dynamic nature of polymeric 3 was highlighted by its degradation to the η1-N-BTD coordinated monomeric fragment 1, which could also be followed spectrophotometrically in polar protic EtOH. Interestingly, both monomeric 1 and polymeric 3 exhibited efficient electrocatalytic activity toward water oxidation processes (OER, HER) on immobilization on an FTO support, which also divulged the better intrinsic water oxidation activity of 3 in comparison to 1.

Proximal Hyperspectral Imaging Detects Diurnal and Drought-Induced Changes in Maize Physiology.

Hyperspectral imaging is a promising tool for non-destructive phenotyping of plant physiological traits, which has been transferred from remote to proximal sensing applications, and from manual laboratory setups to automated plant phenotyping platforms. Due to the higher resolution in proximal sensing, illumination variation and plant geometry result in increased non-biological variation in plant spectra that may mask subtle biological differences. Here, a better understanding of spectral measurements for proximal sensing and their application to study drought, developmental and diurnal responses was acquired in a drought case study of maize grown in a greenhouse phenotyping platform with a hyperspectral imaging setup. The use of brightness classification to reduce the illumination-induced non-biological variation is demonstrated, and allowed the detection of diurnal, developmental and early drought-induced changes in maize reflectance and physiology. Diurnal changes in transpiration rate and vapor pressure deficit were significantly correlated with red and red-edge reflectance. Drought-induced changes in effective quantum yield and water potential were accurately predicted using partial least squares regression and the newly developed Water Potential Index 2, respectively. The prediction accuracy of hyperspectral indices and partial least squares regression were similar, as long as a strong relationship between the physiological trait and reflectance was present. This demonstrates that current hyperspectral processing approaches can be used in automated plant phenotyping platforms to monitor physiological traits with a high temporal resolution.

Influence of Magnetic Field with Schumann Resonance Frequencies on Photosynthetic Light Reactions in Wheat and Pea.

Photosynthesis is an important target of action of numerous environmental factors; in particular, stressors can strongly affect photosynthetic light reactions. Considering relations of photosynthetic light reactions to electron and proton transport, it can be supposed that extremely low frequency magnetic field (ELFMF) may influence these reactions; however, this problem has been weakly investigated. In this paper, we experimentally tested a hypothesis about the potential influence of ELFMF of 18 µT intensity with Schumann resonance frequencies (7.8, 14.3, and 20.8 Hz) on photosynthetic light reactions in wheat and pea seedlings. It was shown that ELFMF decreased non-photochemical quenching in wheat and weakly influenced quantum yield of photosystem II at short-term treatment; in contrast, the changes in potential and effective quantum yields of photosystem II were observed mainly under chronic action of ELFMF. It is interesting that both short-term and chronic treatment decreased the time periods for 50% activation of quantum yield and non-photochemical quenching under illumination. Influence of ELFMF on pea was not observed at both short-term and chronic treatment. Thus, we showed that ELFMF with Schumann resonance frequencies could influence photosynthetic light processes; however, this effect depends on plant species (wheat or pea) and type of treatment (short-term or chronic).

Differential Changes in D1 Protein Content and Quantum Yield of Wild and Cultivated Barley Genotypes Caused by Moderate and Severe Drought Stress in Relation to Oxidative Stress

The aim of this study was to investigate the effects of drought stress on oxidative damage and efficiency of PSII photochemistry in barley and compare the varietal response of different genotypes including Yusof (tolerant), Moroc9-75 (sensitive), and wild barley (HS) to drought. Plants were subjected to different levels of soil water availability including control, moderate, and severe drought stress. Exposure to drought stress led to decrease in leaf water potential, biomass production, and stomatal conductance (gs) in all genotypes. Drought induced an increase in H2O2 content followed by increase in malondialdehyde (MDA) as a final result of lipid peroxidation. Drought stress also resulted in reduction of D1 protein content in all genotypes and decreased the maximal quantum yield of PSII photochemistry (FV/FM). These parameters were more affected in Moroc9-75 cultivar by drought stress compare to Yusof and HS genotype. Based on our results, drought-induced reactive oxygen species may decrease PSII photochemistry either through peroxidation of thylakoid membranes or interfering with D1 protein synthesis, necessary for proper function of PSII.

Acetylene bridged D-(π-A)2 type dyes containing benzophenone moieties: Photophysical properties, and the potential application as photoinitiators

Acetylene bridged acceptor-π-bridge-donor-π-bridge-acceptor (A-π-D-π-A) dyes (DBPs) based on benzophenone were designed and synthesized via Sonogashira coupling reaction utilizing carbazole/phenothiazine/triphenylamine as electron donating groups. The photophysical properties, photochemistry characteristics, as well as the two-photon absorption properties were studied. All dyes exhibited excellent intra-/intermolecular charge transfer properties upon excitation, and large two photon absorption cross sections in the wavelength range of 720~860 nm. Significant differences in fluorescence and photochemistry properties were found depending on the electron donating groups. The rigid carbazole favored hybridization of benzophenone like local excited state and intramolecular charge transfer excited state, which resulted in abnormal changes in fluorescence quantum yield, poor photostability, and good initiating ability both as Norrish Ⅱ initiator and as sensitizer for iodonium salt. However, the butterfly-shaped phenothiazine and propeller-shaped triphenylamine facilitated intramolecular charge transfer excited states, which resulted in typical positive solvatochromism effect, good photostabilities, and lacking of initiating ability as Norrish Ⅱ initiator.

Effects of Temperature on The UV-B Sensitivity of Toxic Cyanobacteria Microcystis aeruginosa CS558 and Anabaena circinalis CS537.

Rising global temperatures have been suggested to favor cyanobacteria over eukaryotic algae, but UV-B fluxes are also predicted to remain high and may interact with temperature to affect algal growth. To understand the interactive effects of temperature and UV-B radiation, cultures of Microcystis aeruginosa and Anabaena circinalis were grown at either 25 or 30°C and then exposed to an acute irradiance of UV-B (1.4Wm-2 ). Both species showed differences in growth rates at both temperature regimes. The growth rates of M.aeruginosa (0.41±0.02day-1 ) and A.circinalis (0.38±0.01day-1 ) were higher at 25 and 30°C, respectively. Rates of damage (k) and repair (r) were calculated from the kinetics of change in effective quantum yield, Fv '/Fm '. Analysis of the estimates of r and k shows that M.aeruginosa exhibited relatively high values for both parameters, compared to A.circinalis, at both growth temperatures. In both species, repair rates were higher at 30°C than at 25°C but in A.circinalis damage was also greater at the higher temperature. In contrast, M.aeruginosa showed a lower damage rate at the higher temperature. For both species, the ratio of r:k was higher at the higher temperature. However, the percent inhibition of effective quantum yield by UV-B was greater in A.circinalis than in M.aeruginosa as the r:k was lower A.circinalis. Therefore, it could be concluded that temperature may influence growth and bloom formation of cyanobacteria and that different species may respond differently to UV-B and temperature interactions.