The photophysics and photochemical behavior of the phenoxazin-3-one dyes, resazurin and resorufin, have been studied in aqueous solutions. The irradiation of resazurin in the presence of amines leads to deoxygenation of the N-oxide group, giving resorufin. This photoreaction is highly dependent on the amine structure and is efficient only in the presence of tertiary aliphatic amines. The absorption and fluorescence properties of these dyes are dependent on pH. At pH above 7.5 both dyes are in their anionic form. For resorufin this form is highly fluorescent (ΦF = 0.75). At lower pH the fluorescence is strongly reduced. The N-oxide dye presents a very weak fluorescence quantum yield (0.11), which also is reduced at low pH. Flash photolysis experiments allowed characterization of the triplet state and the transients formed after irradiation of these dyes in the absence and presence of amines. The triplet quantum yields are 0.08 for resazurin and 0.04 for resorufin. The photodeoxygenation of N-oxide...

The Excited-State Interaction of Resazurin and Resorufin with Aminesin Aqueous Solutions. Photophysics and Photochemical Reaction¶

Tertiary amines were readily converted into secondary amines through a photoredox-catalyzed N-demethylation, a bioinspired procedure that resembles nature’s enzymatic pathways. Furthermore, the selective oxidation of primary amines as well as primary and secondary alcohols was achieved using photoredox catalysis. The protocols feature low catalyst loadings (1–2 mol %) and offer access to diverse imines and carbonyl compounds.

Photoredox Catalysis as an Efficient Tool for the Aerobic Oxidation of Amines and Alcohols: Bioinspired Demethylations and Condensations

Publisher Summary This chapter provides a brief review on uracil and its chemistry, by no means exhaustive, has pointed out by some selective but typical examples that show uracils and their derivatives possess considerable synthetic potential. In most cases, a few easy reaction steps enable the synthesis of novel and highly interesting types of condensed heterocycles that are difficult to obtain by other synthetic means.

Uracils: Versatile Starting Materials in Heterocyclic Synthesis

Chalcone derivatives as highly versatile photoinitiators for radical, cationic, thiol–ene and IPN polymerization reactions upon exposure to visible light

Asymmetric Cyclization of 2′‐Hydroxychalcones to Flavanones: Catalysis by Chiral Brønsted Acids and Bases

Photochemical oxygen-atom transfer reaction by heterocycle N-oxides involving a single-electron transfer process: oxidative demethylation of N,N-dimethylaniline

Photo-oxidative Cyclisation of 2'-Hydroxychalcones Leading to Flavones Induced by Heterocycle N-oxides : High Efficiency of Pyrimido[5,4-g]pteridine N-oxide for the Photochemical Dehydrogenation.

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Pyrimidines.54. : Ring Transformation of 5-(2-Carbamoylvinyl)uracil Derivatives to 5-Carbamoylpyridin-2-ones.

Efficient oxygen-atom transfer agent: photochemical hydroxylation of benzene derivatives by pyrimido[5,4-g]pteridine n-oxide

Irradiation of appropriately protected purine nucleosides (guanosine and adenosine)(1) and cytidine (2a) in the presence of pyrimido[5,4-g]pteridine N-oxide (5) with u.v.–visible light results in the exclusive formation of the corresponding 5′-O,8-cyclopurine nucleosides (3) and 5′-O,6-cyclocytidine (4a).

Kaoru Shimada

Papers

Photochemical oxygen-atom transfer reaction by heterocycle N-oxides involving a single-electron transfer process: oxidative demethylation of N,N-dimethylaniline

Photo-oxidative Cyclisation of 2'-Hydroxychalcones Leading to Flavones Induced by Heterocycle N-oxides : High Efficiency of Pyrimido[5,4-g]pteridine N-oxide for the Photochemical Dehydrogenation.

Pyrimidines.54. : Ring Transformation of 5-(2-Carbamoylvinyl)uracil Derivatives to 5-Carbamoylpyridin-2-ones.

Efficient oxygen-atom transfer agent: photochemical hydroxylation of benzene derivatives by pyrimido[5,4-g]pteridine n-oxide

Photochemical intramolecular cyclisation of purine and pyrimidine nucleosides induced by an electron acceptor