Effects of excitation power density on the Stern-Volmer constant measurement.

The Stern-Volmer constant (KSV) is an important parameter to describe the capability of energy transfer to oxygen for porphyrin and its derivatives. By fitting Stern-Volmer equation, IP0/IP = 1 + KSV[O2], the KSV is generally determined through phosphorescence intensities (IP) under aerobic and oxygen-free conditions. In this work, the effect of excitation power density on the KSV measurement is theoretically analyzed and experimentally studied, using palladium octaethylporphyrin (PdOEP) as an example. The IP of PdOEP increased nonlinearly with excitation power density, and the power dependent slope of IP0/IP could be obtained. By way of the functional relationship between the slope of IP0/IP and power density, the real KSV of PdOEP was fitted to be 58 ± 2 kPa-1. The oxygen-dependent phosphorescence lifetimes (τP) and IP under a weak excitation power are also measured to calculate the real KSV, which verifies our analysis.

Accurate Determination of the Photosensitizer Stern-Volmer Constant by the Oxygen-Dependent Consumption of 1,3-Diphenylisobenzofuran.

Because of the absence of phosphorescence, the Stern-Volmer constant (KSV) of the photosensitizer is hard to determine accurately. Although the delayed fluorescence and correlated fluorescence methods have been proposed to determine KSV, the weak signal detection and non-uniform excitation enlarged the measurement error. In this work, a method was proposed to accurately determine KSV by oxygen-dependent consumption of 1,3-diphenylisobenzofuran. The consumption time (δ), as a measurable quantity, is introduced and could be obtained by the absorption spectrum with a high signal-to-noise ratio. Analytically, δ is linearly related to the inverse of oxygen content, and the ratio of the intercept to the slope equals KSV. Experimentally, rose Bengal was selected to perform this determination; the KSV is measured to be 43(1) kPa-1, and the error is reduced by 1 order of magnitude. In addition, metalloporphyrin was used to verify this method.

Experimental Verification of the Accuracy of Oxygen-Varying Correlated Fluorescence for Determining the Quenching Constant KSV.

The oxygen-varying correlated fluorescence provides an effective strategy to gain the quenching constant KSV for a non-phosphorescent system. Owing to the absence of detectable phosphorescence emission in general optical spectroscopy, the facticity of this method has never been verified. Here, the correct way to determine KSV by oxygen-varying correlated fluorescence was systematically studied in detail. We selected gadolinium protoporphyrin IX (Gd-PpIX) to establish a fluorescence and phosphorescence dual emission system. Then, KSV of Gd-PpIX can be obtained by the change of fluorescence intensity (IF) with oxygen concentration using the method of correlated fluorescence at intense pump power; meanwhile, the value can also be determined from the relationship of the phosphorescence intensity ratio and oxygen content by the Stern-Volmer equation under relatively low power density. It was found that the KSV values obtained by the above two methods were 12.2(1) and 11.9(7) kPa-1, respectively. Our results successfully verified the accuracy of oxygen-varying correlated fluorescence for determining the KSV by the phosphorescence property and fluorescence saturation of Gd-PpIX.

Insight into the Heavy Atom Effect Induced by Environmental Heavy Atoms for Gadolinium-Labeled Hematoporphyrin Monomethyl Ether.

Environmental heavy atoms can further enhance the room temperature phosphorescence (RTP) emissions of gadolinium-labeled hematoporphyrin monomethyl ether (Gd-HMME) by way of the external heavy atom effect (HAE). However, the macroscopic phosphorescence intensity covered the intrinsic effect of the environmental heavy atoms. In this study, a method of separating the external HAE from the total is performed, and a quantity to describe the intrinsic nature of external HAE is defined. The environmental Gd3+ concentration evolution of the phosphorescent transition rate (kP) is obtained by correlated absorption, emission, and time-resolved spectroscopy. The kP increases linearly with environmental Gd3+ concentration, while the intercept kP0 coincides with that of the internal HAE. The slope κ could be calculated, and it is a quantity free of the Gd3+ concentration and only relies on the type of environmental heavy atoms. In addition, the environmental Lu3+ exhibits similar functionality to Gd3+ in external HAE. Environmental Pd2+ quenches the phosphorescence intensity macroscopically, while it enhances the HAE intrinsically. Our method provides an alternative insight into the intrinsic nature of environmental heavy atoms.

Intrinsic Characterization Method on the Heavy Atom Effect of Metalloporphyrins.

The presence of room temperature phosphorescence emission in metalloporphyrin, via the transition from the excited triplet state (T1) to the ground state (S0), relies on the chelated heavy metal ions, which is known as the heavy atom effect (HAE). Despite the HAE being a reliable method to tune the phosphorescence process widely, the realization of the HAE nature is a tough task as the induced phosphorescence process is sensitive to not only the specie of bonded heavy atoms but also chemical environments such as the oxygen quenching and solvent effect. In this study, we have aimed at a quantitative determination of the intrinsic phosphorescent transition rate (kP) in metalloporphyrin gadolinium-labeled hematoporphyrin monomethyl ether (Gd-HMME). After the theoretical analysis based on the rate equation model to remove the nonintrinsic contribution and the experimental results of phosphorescence, the kP is calculated to be ∼2.4 × 10-4 µs-1. This study enables us to approach the intrinsic energy characteristic of metalloporphyrins; moreover, our work provides an effective pathway for the further optimization of the varied functional metalloporphyrin.

Study on the origin of linear deviation with the Beer-Lambert law in absorption spectroscopy by measuring sulfur dioxide.

In accordance with the Beer-Lambert law, absorbance is proportional to concentration and optical path length of the absorbers in the sample, and in a linear relationship with total column concentration (product of concentration and optical path length) at a single wavelength. However, limitation of spectral resolution will result in linear deviation with the Beer-Lambert law in actual measurement. Regarding additivity of polychromatic light intensity as the theoretical basis, this paper attributed linear deviation with the Beer-Lambert law to spectral resolution, concentration and light intensity, and verified this explanation by measuring sulfur dioxide at various total column concentrations using spectrometers with different spectral resolutions in the waveband range of 216-230 nm. It was found that linear deviation with the Beer-Lambert law was in negative correlation with spectral resolution, and in positive correlation with total column concentration, and absorbance could be considered to be linear with total column concentration (below 171.4 mg/m2) of sulfur dioxide in the wavelength range of 216-230 nm. In addition, it was also proved that linear deviation increases with decreasing light intensity at a fixed sulfur dioxide column concentration.

Oxygen-Varying Correlated Fluorescence for Determining the Stern-Volmer Constant of Porphyrin.

The achievement of the Stern-Volmer constant (KSV) of porphyrin, a parameter to describe the ability of energy transfer to oxygen, enables us to understand and engineer the functionalities of porphyrin. In this study, we propose a new method to obtain KSV by steady fluorescence based on the population correlation between the excited triplet state (T1) and the singlet excited state (S1). Nonlinear fluorescence intensity of porphyrin [hematoporphyrin monomethyl ether (HMME)] as a function of pump power is observed, and this nonlinearity is oxygen-concentration-dependent. These observations originated from the population correlation, where more intense pump power introduces a stronger population correlation. Most importantly, we have found that the oxygen content can influence this correlation via the quenching of T1 based on its sequent change of fluorescence intensity; KSV ∼ 28 kPa-1 can be obtained theoretically for HMME. Our investigation not only offers a promising method of achieving KSV conveniently by steady fluorescence but also enlightens the advances of regulable fluorescence correlation.

Measurement of CS2 Absorption Cross-Sections in the 188-215 nm Region at Room Temperature and Atmospheric Pressure.

Carbon disulfide, an important sulfur-containing species, has strong absorption lines in the wavelength range of 188 nm to 215 nm. It is difficult to accurately measure the absorption cross sections of carbon disulfide because carbon disulfide will be easily converted into carbon sulfide when it is exposed to ultraviolet light. In this study, the absorption cross sections of carbon disulfide were measured by reducing carbon disulfide conversion. The factors affecting carbon disulfide conversion, including gas flow rate, ultraviolet light intensity, and duration of illumination, were studied to reduce the conversion of carbon disulfide by controlling experimental conditions in the experiment. Finally, the absorption cross sections of carbon disulfide at room temperature and atmospheric pressure were calculated using the absorption spectrum and the carbon disulfide concentration in the absence of carbon disulfide conversion. The wavelengths of 16 absorption peaks on the carbon disulfide absorption cross sections of the vibration change were marked. Carbon disulfide has the maximum absorption cross section of 4.5 × 10-16 cm2/molecule at a wavelength of 198.10 nm.

Optical H2S and SO2 sensor based on chemical conversion and partition differential optical absorption spectroscopy.

An optical sensor based on chemical conversion and partition differential optical absorption spectroscopy is developed to detect hydrogen sulfide (H2S) and sulfur dioxide (SO2) gas in sulfur hexafluoride (SF6) decomposition products. Given that the absorption cross sections of SO2 and H2S overlap in 170-230 nm band, the differential lines of H2S are very few, meanwhile the corresponding absorption cross sections are small in comparison to that of SO2, thus H2S can be detected by reacting with oxygen to convert to SO2 in the presence of UV light. Through the concentration variation of SO2 before and after chemical reaction, the concentration of H2S can be obtained. Meanwhile the partition differential optical absorption spectroscopy method deduced from Beer-Lambert's law is introduced to weaken the influence of electronic noise on the measuring result, especially in low concentration. The SO2 detection limit of 12 ppb per meter can be achieved. The optical sensor can measure the concentrations of H2S and SO2, so it is suitable for the fault diagnosis of gas insulated switchgear (GIS).