Thermal and Photochemical Stability

Organic dyes like fluorescein and TRITC and the majority of NIR fluorophores suffer from poor photostability [77]. In addition, many NIR dyes, such as clinically approved indocyanine green (ICG) reveal poor thermal stability in aqueous solution [78]. Moreover, the presence of ozone can result in dye decomposition as observed for Cy5 [79]. In the last years, many organic dyes like the Alexa dyes have been 

The thermal and photochemical stability of both organic dyes and nanocrystals are influenced by an extremely broad variety of conditions that need to be considered excitation wavelength and intensity, matrix or microenvironment, label concentration, and, in the case of nanoparticles, surface chemistry. Therefore, the individual study of the stability of a chromophore under the conditions required can usually not be avoided. 

In general, dipnictines react cleanly with sulfur, selenium, or tellurium to afford corresponding chalcogen (Ch) insertion products of general formula RjPn-Ch-PnRj. Such reactions occur with 

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Fused bridge prevents isomerisation and provides thermal and photochemical stability I------------------------------1... 

Assessing thermal and photochemical stability is important. Thermal stability can be readily measured by measuring properties such as second harmonic generation as a function of heating at a constant rate (e.g., 4-10 °C/min) [121]. The temperature at which second-order optical nonlinearity is first observed to decrease is taken as defining the thermal stability of the material [2,3,5,63,63]. It is important to understand that the loss of second-order nonlinear optical activity measured in such experiments is not due to chemical decomposition of the electro-optic material but rather is due to relaxation of poling-induced acentric... 

A number of researchers have recently commenced study of the thermal and photochemical stability of organic EO chromophores [87,92,309-312]. It is not clear that an agreed upon mode of assessment has been arrived at that will be applicable to a wide range of device applications. Many studies are being performed on materials that are not likely relevant to the fabrication of devices. The final assessment of thermal and photochemical stability may well have to be per-... 

In this case, decomposition should be induced by appropriate radical traps such as 02. The results of numerous studies on the thermal and photochemical stabilities of alkylcobalamins as well as of model compounds are consistent with this.) (5, 6, 7, 8). 

Finally, in the context of these results, the well recognized, apparently lower thermal (and photochemical) stability of secondary cobalt-alkyls, relative to primary ones, may reflect the greater accessibility of irreversible decomposition pathways involving olefin elimination (i.e., through schemes such as that in Reactions 25-26), in addition to some probable lowering of the metal-alkyl bond-dissociation energy. 

Germoles 56 undergo cycloaddition reaction with the wide range of dienophiles shown the thermal and photochemical stability of the adducts were examined <2000RCB1275>. 

Thermal and Photochemical Stability. Kinetically stabilized silaaromatic species shown in Scheme 53 showed some difference in their stability in solntion (Schemes 57... 

Girois, S., Effect of Iron Gompounds on PVG (Thermal and photochemical stability). Paper at Antec 1999, p. 3604... 

TransitiOn-metal catalyst residues are also important sensitizers, particularly in polyolefins produced by the new gas-phase process. Recently Allen et obtained good correlations between the thermal and photochemical stabilities... 

Oligophenylene rods [92, 112] have attracted much interest as spacers [113], because of their thermal and photochemical stability, and their interesting tunable photophysical properties. Until recently their use as bridging ligands was limited to species containing only one or two phenylene units (see compounds 23-26, Figure 8) because of synthetic difficulties related to solubility problems [24, 33, 74, 97, 114-117]. 

The mechanisms of the thermal and photochemical degradation of poly(vinyl chloride) (PVC) continue to be active areas of research in polymer chemistry mainly because its high chemical resistance, comparatively low cost and wide variety of application m e PVC one of the most widely used thermoplastic materials. The wide variety of forms which the material can take includes pastes, lattices, solutions, films, boards and moulded and extruded pieces and depends to a very large extent on the good electrical and mechanical properties of the polymer. In spite of these advantages the even wider application of the material has been restricted by its low thermal and photochemical stability. Thermal instability is a problem since processing of the polymer is carried out at about 200 C and the photochemical instability places a limit on the extent of the outdoor applications which can be developed. 

In the second part of the present work we have investigated the thermal and photochemical stabilities of the siliranes synthesized in the first part of the study. Photolysis experiments with the siliranes demonstrate that all of these molecules are photolabile. In general, the product mixtures were so complex that mostly only those compounds could be identified that were, in part, formed... 

However, apart from large nonlinearities, many other essential parameters, including a good thermal and photochemical stability, low optical loss (high transparency), and good processability, need to be simultaneously optimized for the active material to be incorporated in a practical device. 

Improvements in thermal and photochemical stability have been achieved by using conformationally locked polyenes [41,42] by incorporating the polyene chain into ring systems such as isophorone [43] or by introducing heterocyclic conjugating units such as thiazole [44], furan, and thiophene [45]. Many studies have investigated the... 

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