Singlet oxygen-sensitized delayed fluorescence of common water-soluble photosensitizers

Abstract

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.

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

“…We propose that this effect is the result of singlet‐oxygen accumulation. Another theoretically possible explanation would be singlet‐oxygen‐sensitized delayed fluorescence (SOSDF),41 but the effect is unlikely to be very efficient at such unfavorable ratios of dye and oxygen concentrations. However, considering the overall small amount of delayed fluorescence generated by this effect, it was not possible for us rule out the effect of this phenomenon because the used dyes already exhibit strong e‐type delayed fluorescence and the influence of SOSDF (if any) could therefore not be quantified.…”

Photosensitized singlet oxygen generation and detection: Recent advances and future perspectives in cancer photodynamic therapy

“…Recently, time‐resolved microscopic detection of SOSDF from single living 3T3 mouse fibroblasts incubated with 100 µM TPPS4 and TMPyP has been successfully achieved, which suggests that SOSDF can be considered as a promising semi‐direct method for 1 O 2 detection in biological environments. Although this semi‐direct method generally exhibits much stronger signal than NIR 1 O 2 luminescence for detection, the specificity for 1 O 2 detection is still a great challenge . Therefore, only direct 1 O 2 luminescence measurement will be discussed in detail here.…”

Parallel fluorescence and phosphorescence monitoring of singlet oxygen photosensitization in rats

“…This setup, equipped by bifurcated lightguide with°uorescence probe, was successfully used to detect NIR luminescence of PSs and singlet oxygen from living mammalian cells in our previous paper. 32 The holder is equipped by ports for additional bers to enable simultaneous detection of other luminescence signals, for instance detection of timeresolved infrared phosphorescence or delayed°uo-rescence 42,43 of PS to obtain additional information about kinetics of the PS triplets. However, in this experiment the additional ports were sealed o® due to the lack of additional detectors.…”