Charles University in Prague, Faculty of Mathematics and Physics, Department of Chemical Physics and Optics, Ke Karlovu 3, 121 16 Praha 2, the Czech Republic.
Photochem Photobiol Sci. 2013 Oct;12(10):1873-84. doi: 10.1039/c3pp50170a.
Six common water-soluble singlet oxygen ((1)O2) photosensitizers - 5,10,15,20-tetrakis(1-methyl-4-pyridinio) porphine (TMPyP), meso-tetrakis(4-sulfonathophenyl)porphine (TPPS4), Al(III) phthalocyanine chloride tetrasulfonic acid (AlPcS4), eosin Y, rose bengal, and methylene blue - were investigated in terms of their ability to produce delayed fluorescence (DF) in solutions at room temperature. All the photosensitizers dissolved in air-saturated phosphate buffered saline (PBS, pH 7.4) exhibit easily detectable DF, which can be nearly completely quenched by 10 mM NaN3, a specific (1)O2 quencher. The DF kinetics has a biexponential rise-decay character in a microsecond time domain. Therefore, we propose that singlet oxygen-sensitized delayed fluorescence (SOSDF), where the triplet state of a photosensitizer reacts with (1)O2 giving rise to an excited singlet state of the photosensitizer, is the prevailing mechanism. It was confirmed by additional evidence, such as a monoexponential decay of triplet-triplet transient absorption kinetics, dependence of SOSDF kinetics on oxygen concentration, absence of SOSDF in a nitrogen-saturated sample, or the effect of isotopic exchange H2O-D2O. Eosin Y and AlPcS4 show the largest SOSDF quantum yield among the selected photosensitizers, whereas rose bengal possesses the highest ratio of SOSDF intensity to prompt fluorescence intensity. The rate constant for the reaction of triplet state with (1)O2 giving rise to the excited singlet state of photosensitizer was estimated to be ~/>1 × 10(9) M(-1) s(-1). SOSDF kinetics contains information about both triplet and (1)O2 lifetimes and concentrations, which makes it a very useful alternative tool for monitoring photosensitizing and (1)O2 quenching processes, allowing its detection in the visible spectral region, utilizing the photosensitizer itself as a (1)O2 probe. Under our experimental conditions, SOSDF was up to three orders of magnitude more intense than the infrared (1)O2 phosphorescence and by far the most important pathway of DF. SOSDF was also detected in a suspension of 3T3 mouse fibroblast cells, which underlines the importance of SOSDF and its relevance for biological systems.
六种常见的水溶性单重态氧（1O2）敏化剂——5,10,15,20-四（1-甲基-4-吡啶𬭩）卟啉（TMPyP）、meso-四（4-磺基苯基）卟啉（TPPS4）、Al（III）酞菁氯四磺酸（AlPcS4）、曙红 Y、玫瑰红和亚甲基蓝——在室温下的溶液中产生延迟荧光（DF）的能力方面进行了研究。所有溶解在空气饱和磷酸盐缓冲盐水（PBS，pH7.4）中的敏化剂都表现出容易检测到的 DF，可以被 10mMNaN3（一种特定的 1O2淬灭剂）几乎完全猝灭。DF 动力学在微秒时间域内具有双指数上升-衰减特征。因此，我们提出了单重态氧敏化延迟荧光（SOSDF），其中敏化剂的三重态与 1O2反应，导致敏化剂的激发单重态，是主要的机制。通过其他证据进一步证实了这一点，例如三重态-三重态瞬态吸收动力学的单指数衰减、SOSDF 动力学对氧浓度的依赖性、氮气饱和样品中不存在 SOSDF 或同位素交换 H2O-D2O 的影响。曙红 Y 和 AlPcS4 在所选择的敏化剂中表现出最大的 SOSDF 量子产率，而玫瑰红则具有最高的 SOSDF 强度与瞬时荧光强度之比。估计引发敏化剂激发单重态的三重态与 1O2 的反应速率常数为~/>1×10(9)M(-1)s(-1)。SOSDF 动力学包含关于三重态和 1O2 寿命和浓度的信息，这使其成为监测敏化和 1O2 猝灭过程的非常有用的替代工具，允许在可见光谱区域进行检测，利用敏化剂本身作为 1O2 探针。在我们的实验条件下，SOSDF 的强度比红外 1O2 磷光高达三个数量级，是 DF 最重要的途径。SOSDF 也在 3T3 小鼠成纤维细胞悬浮液中被检测到，这强调了 SOSDF 的重要性及其与生物系统的相关性。
