Poly photostability

The high photostability and acute fluorescence intensity are two major features of DDSNs compared to dye molecules in a bulk solution. The early DDSN studies have focused on these two properties [8, 13]. For example, Santra et al. studied the photostability of the Ru(bpy)32+ doped silica nanoparticles. In aqueous suspensions, the Ru(bpy)32+ doped silica nanoparticles exhibited a very good photostability. Irradiated by a 150 W Xenon lamp for an hour, there was no noticeable decrease in the fluorescence intensity of suspended Ru(bpy)32+ doped silica nanoparticles, while obvious photobleaching was observed for the pure Ru(bpy)32+ and R6G molecules. To eliminate the effect from Brownian motion, the authors doped both pure Ru(bpy)32+ and Ru(bpy)32+-doped silica nanoparticles into poly(methyl methacrylate). Under such conditions, both the pure Ru(bpy)32+ and Ru(bpy)32+ doped silica nanoparticles were bleached. However, the photobleaching of pure Ru(bpy)32+ was more severe than that of the Ru(bpy)32+ doped silica nanoparticles. 

Similarly, fluorescent silver clusters could be prepared in so called molecular hydrogels, formed by polyglycerol-b/oc -poly(acrylic acid) (PG-b-PAA), using a ratio COOH Ag of 2 1 with UV irradiation (365 nm). The emission band centered at 590 nm reached a maximum after 200 min of irradiation. The authors claim improved photostability of the clusters since they are still luminescent even after 9 h of irradiation, but it has to be mentioned that the irradiation source was weak, only 0.5 mW/cm2. They claim that it is the number of arms in the star polymer rather than the length of the arms (thus the density of COOH) that plays a crucial role in the formation of silver clusters [30]. 

Hie dye-doped ORMOSIL materials exhibit much higher photostability than the reported polymer-doped materials. For example, optical gain was reported for several coumarin dyes in PMMA (13), It is significant to note that the best dyes reported could only be used to several hundred pulses and that most of the coumarin dyes could not even oscillate for 100 pulses. The ORMOSIL gels thus represent an improvement of at least 1-2 orders of magnitude in photostability. Optical gain was also reported for R6G doped into modified poly(methyl methacrylate) (14L These materials exhibited loss of 20% output after 180 pump pulses (1 J/cm ) at 532 nm. The reported plots indicate that these materials would have dropped by 90% after 275-300 pulses due to rapid steady state photodegradation once the pulse count exceeded the critical pulse number. In this case the R6G doped ORMOSIL gel laser offers a useful lifetime improvement by a factor of more than 15 over the reported polymer material. 

Fig. 6. Measurement of photostability of two polymeric electro-optic materials as carried out by researchers at IPITEK (TACAN) Corporation. The data represented by the solid line correspond to the LRD-3 DEC material of Dalton and co-workers [138] while the data represented by open circles correspond to a diaminonitrostilbene chromophore/poly(methyl methacrylate) guest/host material produced by IBM Almaden Laboratories. The dramatic improvement observed for the DEC material can be associated with increased lattice hardness from the chromophore coupling to adjacent polymer chains...

From studies on the polymerization behavior of four-center photopolymerizations in the crystalline state, several remarkable features have been found which suggest significant participation of the crystal lattice in polymerization. For example, the plate-like crystals of DSP (a) obtained by recrystallization from solution photopolymerize in the crystalline state whereas DSP crystals (y) obtained through sublimation are needle-like and do not undergo any photochemical change20. Moreover, plate-like crystals of DSP and P2 VB, and crystals of poly-DSP and poly-P2 VB respectively are very similar to each other in their major X-ray diffraction peaks (Fig. 9)8,40). X-Ray analyses of the crystal structures of several diolefinic compounds, including photostable DSP (y) crystals, have been performed mostly by Nakanishi and Sasada26,4151). 

Hsu ER, Gebert MS, Becker NT, Gaermer AL. Effects of plasticizers and titanium dioxide on the properties of poly(vinyl alcohol) coatings. Pharm Dev Technol 2001 6(2) 277-284. Kakinoki K, Yamane K, Teraoka R, et al. Effect of relative humidity on the photocatalytic activity of titanium dioxide and photostability of famotidine. J Pharm Sci 2004 93(3) 582-589. Sayre RM, Dowdy JC. Titanium dioxide and zinc oxide induce photooxidation of unsaturated lipids. Cosmet Toilet 2000 115 75-80, 82. 

Poly(methyl methacrylate) Is Intrinsically a less photostable polymer than PS Its g Is on the order of 0.07 In aerated dloxane or methylene chloride. An MMA-unlt In a PS chain may thus constitute a weak link In that chain. In P(S-alt-MMA) and In P(S-co-MMA)(3 97). essentially every photon absorbed by the polymer Is absorbed by an S-unlt situated next to an MMA unit. 

The photooxidation and photodegradation of polymers continues to attract some interest but is not as widespread as in previous years. Review articles have appeared dealing with poly(2,6-dimethyl-l,4-phenylene oxides) , photocatalyst fibres, polymers with azo links and accelerated weathering specifications. Other articles of interest include the design of an integrating sphere for repeatability in polymer ageing and the use of FTIR for monitoring the photostability of clearcoats . 

Poly(acrylates) and (alkyl acrylates) - Fluorinated acrylics are inherently photostable while the vacuum UV photolysis of PMMA results in de-esterification and double bond formation ". The stereostructure of PMMA also has an important influence on the product distribution. X-Ray and UV exposure of PMMA was fingerprinted via FT NMR analysis. ... 

Our interest in polymer photodegradation has led us to an investigation of the competition for migrating energy by chain impurities and "defects" such as excimer-forming sites. To isolate the intrachain phenomena, photooxidation of polymer solutions in dimethoxymethane have been carried out. As an example of a very photostable excimer-forming polymer, PS has been selected. Since poly(methyl methacrylate) (PMMA) is known to be far less stable than PS on a quanta-absorbed basis, MMA units have been incorporated into the chain to act as weak links. For energy sinks, 1-VN and 2-VN units have been made part of the chain. 

As discussed in the accompanying article [97], (poly)nucleotides, especially those building Watson-Crick pairs, are uniquely photostable (see also [33,120,121]). The Zn world concept explains this unique photostability by the role of the UV light not only as an energy source, but also as a selective factor during the first evolutionary steps. The unique photostability of (poly)nucleotides finds no explanation in any other hypothesis on the origin of life. 

Koch ATH, Harrison NT, Haylett N, Daik R, Feast WJ, Friend RH. Enhanced photostability of poly(l,3-phenylene diphenylvinylene)-derivatives by diphenyl-substitution. Synth Met 1999 100(l) 113-22. 

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