Chemically Induced Electron and Nuclear Polarization

Scavenging of Organic C-Centered Radicals by Nitroxides

“…Using Kaptein rules, , the products can be identified and the various reactions involved can be unveiled. Moreover, the time-resolved CIDNP version allows measurements of reaction rate constants with microsecond time resolution. − Using the example of N53 and R1, Fischer et al showed that the TR-CIDNP experiments are suitable for the determination of the k c values. The experimental setup for TR-CIDNP has been described in detail .…”

“…Laser flash photolysis of degassed dialkyl ketone solutions inside the NMR spectrometer probehead provides a convenient, clean, and “instantaneous” source of C-centered radicals. The NMR spectra of the reaction products are recorded in the absence and in the presence of nitroxide and at different time delays between the laser pulse and radio frequency pulse τ 0 . − The measurements of the CIDNP intensity of the alkoxyamine on time delay τ 0 provide the observed alkoxyamine formation rate constant k obsd . The dependence of k obsd on the nitroxide concentration provides the value of k c , and that can be obtained using eq displayed in section .…”

Direct Observation of All Open-Shell Intermediates in a Photocatalytic Cycle

“…This observation indicates that radical cation R1• originates from the geminate radical pairs generated by excited-state SET, which provides direct evidence for the electron transfer step (Figure C). Remarkably, the observed absorption/emission (A/E)-type polarization pattern in both cases (see Figure S7 for detailed analysis) indicates that photoinduced SET with both photocatalysts occurs through the formation of an initial singlet radical pair ( 1 RP) − supported by a triplet quenching experiment (Figure S15). Thus, the singlet excited states of both [Ir­(dF-CF 3 -ppy) 2 (dtbbpy)]­PF 6 and 4CzIPN had a significant contribution to their photoredox activity in this reaction, which is in line with a recent study on the photoinduced SET between 4CzIPN and azide anion .…”