Efficiency of singlet oxygen generation from the triplet states of nitrophenyl ethers

Mir, Miquel; Jansen, Lisinka; Wilkinson, Frances; Bourdelande, J. L.; Marquet, Jacques

doi:10.1016/s1010-6030(97)00325-0

Cited by 14 publications

(14 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It is well-known that singlet oxygen is produced with varying efficiency as a consequence of quenching of both excited singlet and triplet states. Despite the intense research carried out over the last three decades on the mechanisms of quenching of electronically excited states by molecular oxygen, several aspects remain unclear. − In a recent compilation 1 of the quantum yields for the photosensitized formation of the lowest electronically excited state of molecular oxygen in solution, we reported the quantum yields of singlet oxygen production, Φ Δ , of 755 different compounds in a wide range of solvents. Despite all these data the reasons why certain compounds yield singlet oxygen with high and others with low efficiency is far from obvious.…”

Section: Introductionmentioning

confidence: 99%

“…The rate constants for quenching of singlet and triplet states by oxygen, and , respectively, and the fractions of triplet states quenched by oxygen that yield singlet oxygen, f Δ T , have been shown to depend on several factors including the excited state energy, the nature of the excited state, the redox potential of the excited state and the nature of the solvent. − …”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Mechanism of Quenching of Triplet States by Molecular Oxygen: Biphenyl Derivatives in Different Solvents

1999

Self Cite

View full text Add to dashboard Cite

The bimolecular rate constants for oxygen (O2(3Σg -)) quenching and the efficiencies f Δ T with which singlet oxygen (O2*(1Δg)) is thereby produced are reported for a range of substituted biphenyl triplet states in acetonitrile, benzene, and cyclohexane. The magnitudes of and f Δ T are inversely correlated, and both parameters exhibit pronounced sensitivity to the oxidation potential ( ) of the biphenyl derivative and to the solvent polarity. It has been observed that the quenching rate constant increases as the oxidation potential of the biphenyl derivative decreases and increases as the solvent polarity increases whereas the efficiency of singlet oxygen production increases with the oxidation potential and decreases with increasing solvent polarity. When solvent viscosity changes are allowed for by calculating the diffusion controlled rate constant, k d, it is established that /k d values are comparable when the electrostatic interaction energy of charge transfer complexes are taken as 0, 3, and 20 kJ mol-1 for acetonitrile, benzene, and cyclohexane, respectively. An improved charge transfer mediated mechanism of quenching based on singlet and triplet channels for oxygen quenching is invoked to discuss these results with the triplet channel only operating when charge transfer is favorable. However, to get a good fit to the data, it is necessary to introduce direct formation of singlet oxygen production from the singlet encounter complexes in competition with charge transfer assisted singlet oxygen production. The free energy of activation for charge transfer assisted quenching by oxygen via singlet and triplet channels is shown to have a linear dependence on the free energy change for full charge transfer, but the indications are that quenching is via singlet and triplet charge transfer complexes with only partial charge transfer character being 12.5%, 14.5%, and 17% in acetonitrile, benzene, and cyclohexane, respectively. An explanation is offered as to why the less polar solvents show the larger fractional charge transfer in the transition states involved in the quenching mechanism.

show abstract

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Mechanism of Quenching of Triplet States by Molecular Oxygen: Biphenyl Derivatives in Different Solvents

1999

Self Cite

View full text Add to dashboard Cite

show abstract

“…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

View full text Add to dashboard Cite

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.

show abstract

“…This situation is discussed, for ex ample, for the triplet state of 3 nitroanisole in acetonitrile with τ Т of 26 ns (k T = 3.8•10 7 s -1 ), since the generation of singlet oxygen by nitroanisoles and nitroveratrole is efficient. 8 The lifetimes of the triplet states of 1 and 2 obtained from the oscillograms are shown in Table 2. The empiri cal parameters of solvents π* (a measure of the ability of a medium to stabilize dipoles) and α (a measure of the ability of a medium to act as a hydrogen bond donor) are used as characteristics of the medium polarity.…”

Section: Resultsmentioning

confidence: 99%

“…8 In this work, the nanosecond laser photolysis tech nique was used to study the properties of the triplet states of 1 (4 nitrophenyl) 3 methylpyrazole (1) and 1 ethyl 3 (4 nitrophenyl) 5 chloropyrazole (2), which have the push pull structure D-Ar-NO 2 bearing the pyrazole fragment as an electron donor. As shown below, the pres ence of a moderately electron donor fragment provides a decrease in the energy of the 3 (π,π*) and 3 (n,π*) levels in these molecules and a noticeable influence of the me dium nature on the spectral kinetic characteristics of their triplet states.…”

mentioning

confidence: 99%

Laser photolysis of 1-(4-nitrophenyl)-3-methylpyrazole and 1-ethyl-3-(4-nitrophenyl)-5-chloropyrazole

2005

View full text Add to dashboard Cite

The spectral kinetic characteristics of the triplet states of 1 (4 nitrophenyl) 3 methyl pyrazole (1) and 1 ethyl 3 (4 nitrophenyl) 5 chloropyrazole (2) were studied by the laser nanosecond photolysis technique in different solvents. The triplet lifetimes (τ T ) of molecules 1 and 2 were found to depend strongly on the solvent nature. An increase in τ T by approximately two orders of magnitude on going from nonpolar and polar aprotic solvents (τ T < 15 ns) to aqueous acetonitrile solutions (τ T = 1100 ns for a volume acetonitrile to water ratio of 1 : 3) was analyzed, taking into account the influence of the medium on the relative contribution of the n,π* and π,π * configurations to the lowest triplet state.Key words: 1 (4 nitrophenyl) 3 methylpyrazole, 1 ethyl 3 (4 nitrophenyl) 5 chloro pyrazole, nanosecond laser photolysis, triplet states, lifetime, solvent effect.

show abstract

Efficiency of singlet oxygen generation from the triplet states of nitrophenyl ethers

Cited by 14 publications

References 33 publications

Mechanism of Quenching of Triplet States by Molecular Oxygen: Biphenyl Derivatives in Different Solvents

Mechanism of Quenching of Triplet States by Molecular Oxygen: Biphenyl Derivatives in Different Solvents

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

Laser photolysis of 1-(4-nitrophenyl)-3-methylpyrazole and 1-ethyl-3-(4-nitrophenyl)-5-chloropyrazole

Contact Info

Product

Resources

About