Chemistry of singlet oxygen. 40. Enhanced molecular oxygen 1O2 formation in cyanoaromatic-sensitized photooxidations by substrate-enhanced intersystem crossing

Photoinduced electron transfer oxygenations

“…580 nm, a shoulder at ca. 440 nm, very close to the known absorption of triplet excited sensitizer aDCA* [203][204][205]. More interestingly, this band shows the same absorption maximum regardless of the substrates.…”

“…In other words, these results clearly show that in the DCA-sensitized photooxidation of specific substrates, the singlet oxygen pathway may compete with the electron-transfer process. This first hint, that singlet oxygen could be a singificant product from the cyanoaromatic-sensitized reactions, was supported by spectroscopic data [204]. In fact, flash photolytic studies on the reaction of trans-stilbene with DCA under nitrogen atmosphere, in polar solvents, and/or in the presence of various additives, reveal, in addition to the well-known absorptions of radical cation (TS*) at 473 nm and radical anion DCA-=) at ca.…”

“…In order to determine the occurrence of energy-transfer processes, such as those reported in Eqs. (42,43), the same group studied the intensity of the singlet-oxygen emission, monitored at 1.27 Ixm, by comparison with that produced with other sensitizers of known quantum yields of singlet oxygen production [204][205][206].…”

Immobilized Organic Photosensitizers with Versatile Reactivity for Various Visible‐Light Applications

“…The absorption spectrum of SG0-PHEN shows three apparent maxima at 340, 400 and 490 nm, all of which have been assigned to the triplet excited state (36): no other transient species are formed upon irradiation. The transient absorption spectra of DCA, although hardly detectable in solution in the absence of heavy atoms to enhance ISC (37,38), could be easily obtained in the silica xerogel SG0-DCA. The absorption maximum should be positioned between the apparent maxima at 390 and 470 nm; consistently, Olea et al (37) reported a triplet-triplet absorption spectrum with maxima at 415 and 445 nm, with a shoulder at 530 nm.…”

Photosensitized Electron-Transfer Reactions of 1-Isopropylidene-2-methylene-3,3-diphenylcyclobutane − [4 + 4] Cycloaddition and Cyclodimerization Initiated by a Buta-1,3-diene Radical Cation Functionality

“…Under the DCA-sensitized conditions, 1 O 2 can be formed by exergonic energy transfer from 1 DCA* to 3 O 2 . [14,15] Apparently, the energy-transfer quenching of 1 DCA* by 3 O 2 in nonpolar benzene occurs much more efficiently than electron-transfer quenching of 1 DCA* by 3, and so photoirradiation of 3 in benzene under oxygen produces 7 in preference to 5 and syn-6. In moderately polar dichloromethane, the electron-transfer process to form syn-6 probably competes with the energy-transfer process to form 7.…”