Quantum yield of singlet dioxygen and elucidation of the quenching mechanism for the reaction between the doublet excited states of tris(bipyridine)chromium(III) and triplet dioxygen

Abstract

Abstract:The formation of singlet dioxygen (lo2) in the reaction between the doublet excited states of tris(bipyridine)chromium(III) and triplet dioxygen in deuterium oxide was detected using near-infrared luminescence corresponding to singlet dioxygen decay. In addition, luminescence intensity measurements were used to determine the quantum yield of singlet dioxygen produced. A value of 0.86 ? 0.08 was obtained for the yield of lo2. Based on these quantum yield measurements, it is proposed that the major quenching mode is energy transfer quenching. However, considering that the lo2 yield is less than unity and electron transfer quenching is not a viable pathway, it is proposed that, in addition to the energy transfer quenching, physical quenching involving spin-catalyzed deactivation of Cr(bpy),,+ may also be operative as a minor quenching pathway.Key words: Cr(bpy)33+, singlet dioxygen, quenching, quantum yield.Resume : Utilisant la luminescence infrarouge correspondant j. la dksactivation du dioxygkne singulet, on a dktectk la formation de dioxygkne singulet ('0,) au cours de la rkaction des Ctats doublement excitks du tris(bipyridine)chrome(III) et du dioxygkne triplet dans l'oxyde de deutkrium. De plus, on a utilisk des mesures d'intensitk de la luminescence pour dkterminer le rendement quantique du dioxygkne singulet produit. On a obtenu une valeur de 0,86 0,08 pour le rendement de lo2. Sur la base de ces mesures de rendements quantiques, il est proposk que le mode majeur de dksactivation soit un transfert d'knergie. Toutefois, si l'on considkre que le rendement en lo2 est plus petit que un et que la dksactivation par un transfert d'klectron n'est pas une voie rkactionelle viable, il est suggkrk que, en plus de la dksactivation par transfert d'knergie, la dksactivation physique impliquant une dksactivation du cr(bpy),,+ catalyske par le spin puisse aussi agir comme voie rnineure de dksactivation.

Uncovering the Roles of Oxygen in Cr(III) Photoredox Catalysis

“…This difference is consistent with minimal photocatalyst turnover for each, but with Ru serving as an initiator for a radical chain (with a radical chain length of roughly 50), whereas Cr only produces approximately stoichiometric product . Reported 3 O 2 quenching rates for excited states in the related complexes [Ru­(bpy) 3 ] 2+ and [Cr­(bpy) 3 ] 3+ are 6.8 × 10 8 and 2.5 × 10 7 M –1 s –1 , respectively, in acetonitrile. , Wrighton and Markham have reported competitive oxygen and aryl alkene quenching in Ru-based systems, , comparable to our observation of competitive quenching by dienophile and oxygen in a Cr-based system. In general, for each photophysical process Ru is faster and/or has a shorter lifetime than the Cr complex studied here.…”

Photosensitized singlet oxygen and its applications

“…Complexes of the form (NN)Pt(II)(SS), where N Ã/N0/bipyridine and 4,4?-ditert-butyl-2,2?-bipyridine, and S Ã/S0/3,4-toluenedithiolate (tdt), meso -1,2-diphenyl-1,2-ethanedithiolate or 1,2-ethanedithiolate produce singlet oxygen with moderate efficiency [43]. In these complexes, the fraction of triplet states quenched by oxygen ranged from 0.11 to 0.20.…”

Photochemistry and Photophysics of Chromium(III) Complexes

“…Acetylacetonato complexes of Cr(III) are similarly effective photocatalysts for the oxygenation of α-pinene. The quantum yield of singlet oxygen generated in quenching of Cr(bpy) 3 3+ by molecular oxygen has recently been measured as 0.86, a greater efficiency than that for the popular oxygen-sensitizer Rose Bengal (φ = 0.80). The authors concluded that in the other 14% of quenching events, spin-catalyzed conversion to the ground states of Cr(bpy) 3 3+ and oxygen occurred.…”