Temperature sensitive quenching

The ruthenium(II) polypyridyl complexes are also popular but the brightnesses do not exceed 15,000 and thermal quenching is rather significant. This property can be utilized to design temperature-sensitive probes providing that the dyes are effectively shielded from oxygen (e.g., in polyacrylonitrile beads). Despite often very high emission quantum yields the visible absorption of cyclometallated complexes of iridium(III) and platinum(II) is usually poor (e < 10,000 M-1cm-1), thus,... 

The temperature sensitivity of phosphorescence mainly arises from fast impurity quenching processes. At low temperatures and rigid glassy medium, emission is a rule rather than exception. 

Non-contact temperature measurement inside microfluidic channels was achieved by using fluorescence quenching of a rhodamine dye. The intensity of the dye fluorescence is temperature-sensitive in a range temperature of 5-95°C [795], Another on-chip temperature measurement method was achieved by measuring... 

Many other fluorophores are temperature-sensitive only when they are bound to macromolecules. Figure 10.16 shows the effect of temperature on the fluorescence intensity of native and guanidine unfolded AEDANS-RNase. Increasing the temperature from 10 to 30°C induces a decrease in fluorescence intensity for both protein states. The intensity decrease in native protein is more affected by temperature than the guanidine-unfolded protein. This thermal quenching is the consequence of rapid movements of the protein structure around the fluorescent probe. These movements occur during the lifetime of the excited state, and their rate is temperature-dependent. 

If we consider the material presented above, we conclude that host-sensitized energy transfer in systems like vanadates, niobates and tungstates can be described satisfactprily by a qualitative model. The actual situation differs from compound to compound due to a difference in the temperature dependence of the exciton diffusion rate. A low value of the quenching temperature of the emission of the intrinsic... 

Temperature Dependence. At room temperature the exponential phosphorescence decay is absent, presumably because of the removal of triplet states by the temperature sensitive quenching process found at low temperatures. The decay from 5 /xsec. to 5 msec, did not fit any simple decay scheme although the mean slope of the decay on a log-log plot was —1. In the first 200 psec. after irradiation the room temperature emission is more intense than at 93 °K. A similar temperature dependence of the luminescence of anthracene crystals has been observed following ultraviolet excitation (1, 23). This behavior was interpreted as being caused by the enhanced intersystem crossing to the triplet states at the higher temperatures. This model, however, would not explain why the luminescence intensity of hot adenine powder in Figure 7 was lower than... 

During many commercial procedures, a concern exists for heterogeneous nucleation and precipitation during continuous cooling. Quench factor analysis has been developed to use the entire time-temperature-sensitization curve [43]. The quench factor, r, is given by... 

The effects of quench rate on IGC for Al-Gu, Al-Gu-Mg, and Al-Cu-Mg-Mn alloys as well as for austenitic stainless steels is considered to be well-understood [43, 74, 75, 106]. Integration of the effects of precipitation and solute depletion at each temperature during a quench (i.e., quench factor analysis) can be compared to isothermal time-temperature-sensitization diagrams in order to predict the quench rate required to avoid IGC [43, 74]. Alloys... 

An ideal polymer binder for temperature sensitive layers should eliminate interferences (e.g., by oxygen quenching) and ampUfy the temperature dependency. Ihial pressure- and temperature-sensitive paints have found increasing interest in... 

Examples of europium complexes 30-32 that have been applied in temperature sensors or dual pressure- and temperature-sensitive paints are listed in Table 5. The respective ligand structures are shown in Scheme 7. The temperature dependency is quantified as average luminescence intensity temperature coefficient 7 [%/°C]. Usually, it is determined in a temperature range from 1 to 40 or 50°C. These examples exceed the intensity temperatiue coefficients of other established temperature sensitive probes such as ruthenium(II)-tris-(l,10-phenanthroline) [121]. Generally, the lifetime temperature coefficients are significantly lower. This indicates that thermal quenching of the triplet state of the antenna chromophore plays an important role. Due to the narrow emission band of europium complexes at 615 nm even triple sensors for temperature, oxygen, and pH are achievable [122]. 

Carbon content is usually about 0.15% but may be higher in bolting steels and hot-work die steels. Molybdenum content is usually between 0.5 and 1.5% it increases creep—mpture strength and prevents temper embrittlement at the higher chromium contents. In the modified steels, siUcon is added to improve oxidation resistance, titanium and vanadium to stabilize the carbides to higher temperatures, and nickel to reduce notch sensitivity. Most of the chromium—molybdenum steels are used in the aimealed or in the normalized and tempered condition some of the modified grades have better properties in the quench and tempered condition. 

A significant proportion of the fine chemicals are complex, multifunctional large molecules. These molecules are labile, unstable at elevated temperature, and sensitive towards (occasionally even minor) changes in their environment (e.g. pH). Therefore, processes are needed with inherent protective measures (e.g. chemical or physical quenching) or a precise control system to operate exactly within the allowable range. Otherwise the yield of the desired product can drop to nearly zero. 

A reactor is run adiabatically when no heat is exchanged between the reaction zone and the surroundings. The reaction temperature can then only be controlled by quenching with a cold stream of the reaction mixture or by inter-stage heat exchangers. For highly thermally sensitive large molecules treated in the fine chemicals sector this is a very impractical mode of operation. Therefore, adiabatic reactors will not be discussed here. 

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