Insights Into the Mechanism of Energy Transfer with Poly(Heptazine Imide)s in a Deoximation Reaction

Abstract

Following our previous studies on potassium poly(heptazine imide) (K‐PHI), that is, catalyzed photooxidative [3+2] aldoxime‐to‐nitrile addition to form 1,2,4‐oxadiazoles, we discovered that electron‐rich oximes yield the parent aldehydes instead of target products. In this work, the mechanism of this singlet oxygen‐mediated deoximation process was established using a series of control reactions and spectroscopic measurements such as steady‐state and time‐resolved fluorescence quenching experiments. Additionally, the singlet‐triplet energy gap value was obtained for K‐PHI in suspension, and the reaction scope was broadened to include ketoximes.

Insights into the Role of Graphitic Carbon Nitride as a Photobase in Proton‐Coupled Electron Transfer in (sp3)C−H Oxygenation of Oxazolidinones

“…The phosphorescence peak of lower intensity at ≈540 nm was measured by gating the emission from 40–100 μs with the pulsed xenon lamp. Singlet–triplet energy gap (Δ E ST ), determined as a difference between steady‐state fluorescence and tr‐PL maxima in Figure 5d, is 0.33 eV, which is consistent with the one reported earlier for K‐PHI [42, 45] . A relatively low Δ E ST indicates that the triplet excited state has an energy comparable to the singlet and, in combination with the lifetime exceeding the μs range, we conclude that it is beneficial for the cleavage of C−H bond in oxazolidinones.…”

“…Singlet-triplet energy gap (ΔE ST ), determined as a difference between steady-state fluorescence and tr-PL maxima in Figure 5d, is 0.33 eV, which is consistent with the one reported earlier for K-PHI. [42,45] A relatively low ΔE ST indicates that the triplet excited state has an energy comparable to the singlet and, in combination with the lifetime exceeding the μs range, we conclude that it is beneficial for the cleavage of CÀ H bond in oxazolidinones. The presence of the substrate 1 b and/or O 2 does not quench neither the singlet nor the triplet excited state of mpg-CN (Supporting Information Discussion 1).…”

Einblicke in die Rolle von Graphitkohlenstoffnitrid als Photobase beim protonengekoppelten Elektronentransfer bei der (sp3)C−H‐Oxygenierung von Oxazolidinonen

“…Die Singulett-Triplett-Energielücke (ΔE ST ), die als Differenz zwischen der stationären Fluoreszenz und dem tr-PL-Maxima in Abbildung 5d bestimmt wurde, beträgt 0.33 eV, was mit der für K-PHI berichteten Energielücke übereinstimmt. [42,45] Auf der Nanosekunden-Zeitskala ist das Verhalten des angeregten Zustands von mpg-CN ähnlich wie das von K-PHI, [42] wie die Spuren bei 605, 960 und 1170 nm zeigen (Abbildung 5f). Ähnlich wie bei der tr-PL-Studie zeigte die TAS keine Unterschiede in den elektronischen Signaturen und der Dynamik der angeregten Zustände von mpg-CN, sowohl Singulett als auch Triplett, bei Anwesenheit oder Abwesenheit von O 2 und 1 b (ergänzende Diskussion 1).…”

Light as a Tool in Organic Photocatalysis: Multi‐Photon Excitation and Chromoselective Reactions

“…[47] Recently, the KÀ PHI photocatalyst was shown to activate the substrate even under red light in the deoximation reaction (Figure 10c). [48] The irradiation with longer wavelength was used to improve selectivity for some substrates, such as aliphatic ketoximes. While the reaction was shown to be mostly photochemical under 465 nm irradiation, the photocatalytic mechanism was proved for 625 nm irradiation.…”

“…Recently, the K−PHI photocatalyst was shown to activate the substrate even under red light in the deoximation reaction (Figure 10c) [48] . The irradiation with longer wavelength was used to improve selectivity for some substrates, such as aliphatic ketoximes.…”