Singlet Oxygen-Induced Photodegradation of the Polymers and Dyes in Optical Sensing Materials and the Effect of Stabilizers on These Processes

Abstract

A comprehensive study of photodegradation processes in optical sensing materials caused by photosensitized singlet oxygen in different polymers is presented. The stabilities of the polymers are accessed in the oxygen consumption measurements performed with help of optical oxygen sensors. Polystyrene and poly(phenylsilesquioxane) are found to be the most stable among the polymers investigated, whereas poly(2,6-dimethyl-p-phenylene oxide) and particularly poly(methyl methacrylate) and their derivatives show the fastest oxygen consumption. The effect of the stabilizers (singlet oxygen quenchers) on the oxygen consumption rates, the photostability of the sensitizer, and the total photon emission (TPE) by singlet oxygen is studied. 1,4-Diazabicyclo[2.2.2]octane (DABCO) was found to significantly reduce both the TPE and the oxygen consumption rates, indicating its role as a physical quencher of singlet oxygen. The addition of DABCO also significantly improved the photostability of the sensitizer. The N-alkylated derivative of DABCO and DABCO covalently grafted to the polystyrene backbone are prepared in an attempt to overcome the volatility and water solubility of the quencher. These derivatives as well as other tertiary amines investigated were found to be inefficient as stabilizing agents, and some of them even negatively affected the oxygen consumption rates.

Photosensitisation studies of silicone polymer doped with methylene blue and nanogold for antimicrobial applications

“…Photobleaching of dyes in different polymer matrices has been reported, 29 and MB photobleaching generally results in the formation of a colourless 'leuco' form most likely via Type 1 photoreduction mechanisms, either involving electron transfer from MB or other substrates to the MB triplet state. Photobleaching of dyes in different polymer matrices has been reported, 29 and MB photobleaching generally results in the formation of a colourless 'leuco' form most likely via Type 1 photoreduction mechanisms, either involving electron transfer from MB or other substrates to the MB triplet state.…”

Intrinsic Artefacts in Optical Oxygen Sensors—How Reliable are our Measurements?

“…However, singlet oxygen, which is formed in the photophysical deactivation process, is known to be a highly reactive species. If the matrix, impurities, or the dye itself are prone to oxidation, a certain part of the generated oxygen will be chemically consumed and is therefore no longer available for further photophysical interactions 34. 35 The amount of singlet oxygen, and therefore its reaction rate, is directly proportional to the amount of probe molecules in the excited state (and therefore excitation/light density).…”

“…Polystyrene is widely regarded as a very stable and suitable matrix for optical oxygen sensors. However, in trace sensor systems, even the comparably small reactivity of polystyrene34 has a large impact on the sensor response. One can observe the drastic decrease in sensitivity at higher excitation photon‐flux values and upward bend that is characteristic for oxygen photoconsumption.…”

“…Given the high chemical stability of the porphyrin dye used for this experiment, the deactivation process is most likely based on physical deactivation through the introduced CH bonds. This scenario implies that the introduction of a physical quencher, such as the quenchers proposed by Enko et al.,34 might help to decrease singlet‐oxygen lifetimes, and therefore the magnitude of this phenomenon. Unfortunately, these compounds are usually not soluble in perfluorinated matrices.…”

Following Oxygen Consumption in Singlet Oxygen Reactions via Changes in Sensitizer Phosphorescence

“…It is possible that this approach can be extended to the investigation of singlet oxygen sensitization/depletion processes associated with investigations of in vivo and in vitro oxygen depletion rates and DNA damage process and kinetics via singlet oxygen. Additionally, oxygen consumption associated with polymer degradation is also an area of interest and use of phosphorescent sensitizers of the type used here may be useful in the study of singlet oxygen‐ polymer reactions.…”