Physical and chemical properties of singlet molecular oxygen

Kearns, David R.

doi:10.1021/cr60272a004

Cited by 903 publications

(407 citation statements)

References 38 publications

(52 reference statements)

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“…Several techniques have been used to detect 1 O 2 in condensed phase like 1 O 2 → 3 O 2 NIR phosphorescence [25][26][27][28][29][30][31][32][33], time resolved thermal lens spectroscopy [26,34,35], and the analysis of 1 O 2 specific reaction products [21,29,[36][37][38][39][40][41]. Quantum yields of 1 O 2 production have been investigated for a large number of sensitizers.…”

Section: Introductionmentioning

confidence: 99%

Singlet molecular oxygen photosensitized by Rhodamine dyes: correlation with photophysical properties of the sensitizers

Stracke

Heupel

Thiel

1999

Journal of Photochemistry and Photobiology A: Chemistry

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By measuring its IR phosphorescence the formation of singlet molecular oxygen 1 O 2 photosensitized by rhodamine dyes is directly proved. The 1 O 2 formation rate is compared with that expected from the low probability (≈1%) of intersystem crossing of the photosensitizers. The quantum yield for triplet population and the triplet lifetime of the investigated dyes is measured by using a laser-scanning-microscopy technique. The influence of quenching agents (nitrobenzene and COT) is discussed. It results that the formation of 1 O 2 can be prevented effectively by quenching of the S 1 or T state of the photosensitizer. The influence of the molecular ground-state oxygen 3 O 2 concentration [ 3 O 2 ] is investigated. The presence of the paramagnetic 3 O 2 leads to an increased S 1 →T intersystem crossing rate of the photosensitizers and therefore to a reinforced formation of singlet molecular oxygen. It is found for rhodamine 6G as well as for rose bengal that in air-saturated acetonitrile nearly the half of the excited dye triplets are quenched by molecular oxygen. The 1 O 2 concentration can be significantly reduced by decreasing the 3 O 2 concentration below its air saturated level.

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Section: Introductionmentioning

confidence: 99%

Singlet molecular oxygen photosensitized by Rhodamine dyes: correlation with photophysical properties of the sensitizers

Stracke

Heupel

Thiel

1999

Journal of Photochemistry and Photobiology A: Chemistry

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“…For example, in water, the quenching process of 1 NAD* by molecular oxygen has a rate of 1.08 × 10 10 L mol −1 s −1 while for 3 NAD* it is 1.51 × 10 9 L mol −1 s −1 , about 1/9th that of 1 NAD*, as frequently observed in aromatic systems [51]. Although the details of the quenching mechanism are still not clear, there is general agreement that the mechanism depends on the nature of the system, and involves energy and/or charge transfer leading to the formation of singlet oxygen 1 O 2 [11,52,53], a very reactive species, and possibly superoxide anions. Since no other transient species were detected experimentally by laser flash photolysis, we can presume that energy transfer between 3 NAD* and molecular oxygen leading to 1 O 2 formation is highly favorable.…”

Section: Phosphorescence Spectroscopy and Triplet State Characterizationmentioning

confidence: 77%

Photophysical characterization of the plant growth regulator 2-(1-naphthyl) acetamide

Silva

Wong-Wah-Chung

Sarakha

2013

Journal of Photochemistry and Photobiology A: Chemistry

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a b s t r a c tThe photophysical properties of the widely used plant growth regulator 2-(1-naphthyl) acetamide (NAD) were studied in water and representative organic solvents (ethanol, ethylene glycol, acetonitrile, chloroform, 1,4-dioxane) employing steady-state and time-resolved spectroscopy. Quantum yields and lifetimes of fluorescence, phosphorescence and triplet formation and triplet-triplet absorption spectra were obtained. From these, all radiative and radiationless rate constants have been determined, together with singlet and triplet excited state energies (4.00 and 2.69 eV, respectively). The fluorescence quantum yield and lifetime increased on going from water (˚F 0.066, F 35.0 ns) to non-hydrogen bonding solvents (˚F 0.357, F 51.0 ns in 1,4-dioxane), probably due to decreased internal conversion. Fluorescence was quenched by several anions through an electron transfer process. A limit on the reduction potential of 1 NAD* of E 0 2.1 ± 0.2 V was estimated. The attribution of the transient absorption seen in nanosecond laser flash photolysis to 3 NAD* was confirmed by energy transfer and oxygen quenching. Quenching of triplet states leads to singlet oxygen formation, with quantum yields varying from 0.097 in water to 0.396 in chloroform. However, these are lower than the triplet state quantum yields, particularly in water (˚T 0.424), indicating competing quenching pathways, probably involving electron transfer. The relevance of these results to the photoreactivity of NAD under environmental conditions is discussed.

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“…Singlet oxygen is the lowest electronically excited state and a mutagenic form of molecular oxygen [34]. Structurally NFR is more susceptible to alteration via reaction with singlet oxygen and this is observed with a decrease in the fluorescence of NFR.…”

Section: Determination Of Singlet Oxygen Productionmentioning

confidence: 99%