Many photosensitizers have a singlet oxygen quantum yield (ΦΔ) equal 0.99 (or 1). Does it mean that these photosensitizers are exclusively acting via type II photochemical reactions?
(ΦΔ=1 → exculsive singlet oxygen producer ???)
It depends on the nature of the sensitizer S and of the system in which it is located, especially the presence or absence of any compound capable of interacting with the triplet state of S in competition with oxygen
Thanks Mr. Tanielian for your answer.
It has been reported that phenalenone has 0.94⪕ΦΔ⪕ 1.00 in methanol/water and is considered as reference for singlet oxygen generation. However type I and type II can occur for phenalenone in aqueous media. So ΦΔ=1 → exculsive type II agent is wrong. Am I right ??
I know the results on phenalenone for being one of the authors of the publication. The important parameter is the competition between the reaction of the triplet state with the substrate and oxygen. If the rate constant with the substrate is large enough, there may be a Type I contribution. See Photochemistry and Photobiology, 2000, 71 (1), 12-19 and Photochem. Photobiol. Sci., 2003, 2, 297-305.
Thanks for providing these publications, I will read them.
What about 2-((4-pyridinyl)methyl)-1Hphenalen-1-one known as SAPYR ??
this compound is known as an exclusive singlet oxygen generator. Is that mean singlet oxygen production regardless the system where it is ??
No.The example of m-THPC (Temoporphin,active ingredient of Foscan) shows experimentally that even if ISC~1 the competitive reactions are taking place in bulk media and both pathways exist and coexist.The equilibrium of O radical and O2 Superoxide when established is controlled by thermodynamics at formation and thenafter by distribution to products.Actually ur statement IN QUESTION is erroneous since for this to happen ISC Quantu,m yield should equal singlet oxygen yield.This is an ideal figure in practice!Oxygen Quantum yield doesn't measure ISC yield,it is allways a fraction of:if it`s over 70%-80% than Pathway II predominates Pathway I AND VICE-VERSA.You posed the question like an axiome in math."accordingly":" many photosensitizers have...",these are either erroneous results=artifacts...while in practice no photosensitizer has or can have quantum yield of 1 in singlet oxygen quantum yield !
There is a paper in whihc singlet oxygen yield can be more than 1 . https://pubs.rsc.org/en/content/articlepdf/2016/ra/c6ra05820e
It depends on various factors, like reference photosensitizers, light source, solvent
- Badges
- Science topic
- Similar topics
- Chemistry
- Biochemistry
- Biochemical Techniques
- Blotting Techniques
- Immunoblotting
- Dyes