pH DEPENDENCE OF SENSITIZED PHOTOOXIDATION IN MICELLAR ANIONIC AND CATIONIC SURFACTANTS, USING THIAZINES DYES

Bagno, O.; Soulignac, J.C.; Joussot‐Dubien, Jacques

doi:10.1111/j.1751-1097.1979.tb07823.x

Cited by 10 publications

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“…The lifetime of '02 in ionic micelles [64,126] and the reactivity of '02 in micellar solutions [35,64] do not differ appreciably from those in homogeneous solutions. The micellar outer charges also affect the rate of photoreaction through the adsorption of dye to the micellar surface [6,64] and/or the orientation of reactants within micelles [SS, 1251. The penetrability of '02 may influence the photoreaction rate [34,SO].…”

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confidence: 99%

Dye Binding and Photodynamic Action

Amagasa

1981

Photochem & Photobiology

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A variety of natural and synthetic compounds can act as effective photosensitizers in biological systems, including psoralens, flavins, porphyrins, acridines, phenothiazines, xanthenes, quinones, polyenes, haloaromatics and inorganic ions. These, in the presence of light and oxygen, inactivate and modify the integrity of important biomolecules and cellular structures, leading to cell death, mutation and other special function losses [70,118,119]. Many photosensitizers can act as mediators of photodynamic and non‐photodynamic reactions, depending on the experimental conditions. Although a great variety of photosensitized reactions may occur with different sensitizers and substrates, they can be classified into two types of reaction mechanisms, that is, Type I (radical) and Type II (singlet oxygen; 1O2) mechanisms. Type I and Type II reactions for important biomolecules have recently been reviewed [27, 119].

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Dye Binding and Photodynamic Action

Amagasa

1981

Photochem & Photobiology

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“…One of the earliest studies of substance was performed in the mid-1970s. In this work, the effect of pH on the oxygen-dependent photophysics of thiazine dyes, in particular, methylene blue, was examined. − Upon acidification of this system, protonation occurs at an unsaturated nitrogen atom that is an intrinsic part of the sensitizer chromophore. A decrease in the yield of singlet oxygen in more acidic solutions was correlated to the observation that the rate constant for oxygen quenching of the triplet state of protonated methylene blue was significantly smaller than that for the unprotonated triplet state.…”

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confidence: 99%

Effect of Sensitizer Protonation on Singlet Oxygen Production in Aqueous and Nonaqueous Media

et al. 2007

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The yield of singlet molecular oxygen, O2(a(1)Delta(g)), produced in a photosensitized process can be very susceptible to environmental perturbations. In the present study, protonation of photosensitizers whose chromophores contain amine functional groups is shown to adversely affect the singlet oxygen yield. Specifically, for bis(amino) phenylene vinylenes dissolved both in water and in toluene, addition of a protic acid to the solution alters properties of the system that, in turn, result in a decrease in the efficiency of singlet oxygen production. In light of previous studies on other molecules where protonation-dependent changes in the yield of photosensitized singlet oxygen production have been ascribed to changes in the quantum yield of the sensitizer triplet state, Phi(T), and to possible changes in the triplet state energy, E(T), our results demonstrate that this photosystem can respond to protonation in other ways. Although protonation-dependent changes in the amount of charge-transfer character in the sensitizer-oxygen complex may influence the singlet oxygen yield, it is likely that other processes also play a role. These include (a) protonation-dependent changes in sensitizer aggregation and (b) nonradiative channels for sensitizer deactivation that are enhanced as a consequence of the reversible protonation/deprotonation of the chromophore. The data obtained, although complicated, are relevant for understanding and ultimately controlling the behavior of photosensitizers in systems with microheterogeneous domains that have appreciable pH gradients. These data are particularly important given the use of such bi-basic chromophores as two-photon singlet oxygen sensitizers, with applications in spatially resolved singlet oxygen experiments (e.g., imaging experiments).

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