“…As far as we investigated, there were no exception results of the −Δ G CR dependence of the J in the bimolecular electron transfer systems. There are many other CIDEP studies reported about the signs of the exchange interaction generated by the triplet precursor electron transfer reactions in the polar solvents as listed in Table . ,,− Similar dependence of the signs of the exchange interaction on the −Δ G CR is also seen in the previously reported systems. 5 CW-TREPR spectra observed at 0.5 μs after the laser excitation of the systems of (a) N- methylphenothiazine (3 mM)−1,2,4,5-TCNB (5 mM) in 4:1 v/v mixture of DMSO and glycerol and (b) N -methylphenothiazine (3 mM)−1.4-DCNB (5 mM) in DMSO.…”
Section: Resultssupporting
confidence: 76%
“…There are many other CIDEP studies reported about the signs of the exchange interaction generated by the triplet precursor electron transfer reactions in the polar solvents as listed in Table 3. 9,11,[28][29][30][31] Similar dependence of the signs of the exchange interaction on the -∆G CR is also seen in the previously reported systems.…”
Photoinduced electron transfer reactions were studied by using the continuous wave time-resolved electron paramagnetic resonance and Fourier-transformed electron paramagnetic resonance spectroscopy in polar solvents. The chemically induced dynamic electron polarization was investigated in both singlet and triplet precursor intermolecular electron transfer systems. The signs of the exchange interaction, which are defined by the energy differences between the singlet and triplet radical ion pairs, depended on the free energy changes for the charge recombination processes. The results are interpreted in terms of the mechanism that the spin selective stabilization and destabilization are caused by the perturbation through the electronic coupling from the ground state and the locally excited triplet state of the donor-acceptor pair at the equilibrium nuclear coordinate. In the singlet precursor electron transfer systems, the positive exchange interaction resulted from the selective triplet stabilization in the radical ion pair, when the ion pair state crossed with the locally excited triplet state at the normal region. In the triplet precursor electron transfer systems, the negative exchange interaction resulted from the selective singlet stabilization when the ion pair state crossed with the singlet ground state at the normal region. When the free energy change is larger than about 1.8 eV, the positive exchange interaction resulted from the spin-selective destabilization in the singlet ion pair, since the level crossing occurs at the inverted region.
“…As far as we investigated, there were no exception results of the −Δ G CR dependence of the J in the bimolecular electron transfer systems. There are many other CIDEP studies reported about the signs of the exchange interaction generated by the triplet precursor electron transfer reactions in the polar solvents as listed in Table . ,,− Similar dependence of the signs of the exchange interaction on the −Δ G CR is also seen in the previously reported systems. 5 CW-TREPR spectra observed at 0.5 μs after the laser excitation of the systems of (a) N- methylphenothiazine (3 mM)−1,2,4,5-TCNB (5 mM) in 4:1 v/v mixture of DMSO and glycerol and (b) N -methylphenothiazine (3 mM)−1.4-DCNB (5 mM) in DMSO.…”
Section: Resultssupporting
confidence: 76%
“…There are many other CIDEP studies reported about the signs of the exchange interaction generated by the triplet precursor electron transfer reactions in the polar solvents as listed in Table 3. 9,11,[28][29][30][31] Similar dependence of the signs of the exchange interaction on the -∆G CR is also seen in the previously reported systems.…”
Photoinduced electron transfer reactions were studied by using the continuous wave time-resolved electron paramagnetic resonance and Fourier-transformed electron paramagnetic resonance spectroscopy in polar solvents. The chemically induced dynamic electron polarization was investigated in both singlet and triplet precursor intermolecular electron transfer systems. The signs of the exchange interaction, which are defined by the energy differences between the singlet and triplet radical ion pairs, depended on the free energy changes for the charge recombination processes. The results are interpreted in terms of the mechanism that the spin selective stabilization and destabilization are caused by the perturbation through the electronic coupling from the ground state and the locally excited triplet state of the donor-acceptor pair at the equilibrium nuclear coordinate. In the singlet precursor electron transfer systems, the positive exchange interaction resulted from the selective triplet stabilization in the radical ion pair, when the ion pair state crossed with the locally excited triplet state at the normal region. In the triplet precursor electron transfer systems, the negative exchange interaction resulted from the selective singlet stabilization when the ion pair state crossed with the singlet ground state at the normal region. When the free energy change is larger than about 1.8 eV, the positive exchange interaction resulted from the spin-selective destabilization in the singlet ion pair, since the level crossing occurs at the inverted region.
“…7a) may be due to a slow reaction of the excited triplet state of 4,5-DCPA with alcohol. Ir the triplet relaxes before it reacts with alcohol in this system, then the radical species is observed with a weak absorptive polarization [27]. This mechanism is supported by the slow rise of the absorptive signal due to the slow reaction of the excited triplet state of 4,5-DCPA.…”
Section: 5-dichlorophthalic Anhydride In 2-propanolmentioning
The photoreduction of phthalic anhydride (PA), 3,6-dichlorophthalic anhydride (3,6-DCPA), 4,5-dichlorophthalic anhydride (4,5-DCPA) and tetrachlorophthalic anhydride (TCPA) in 2-propanol has been studied with time-resolved electron paramagnetic resonance. The chemically induced dynamic electron polarization spectra show that the reaction takes place through the excited triplet states. From PA, cyclohexadienyl-type hydrogen adduct and ketyl radicals were observed, whereas 3,6-DCPA produced the 3,6-DCPA anion and hydrogen adduct radicals. With 4,5-DCPA only the anion radical appeared, whilst the TCPA system showed no apparent anion and adduct radical formation. These data show that the hydrogen adduct formation occurs at the 4 position in the benzene ring, but that 4,5-DCPA and TCPA do not undergo this reaction. The anion radicals of PAs are formed in subsequent deprotonation reactions of the ketyl radicals. We propose that the hydrogen adduct radical formation in PA and 3,6-DCPA takes place through direct hydrogen abstraction by the excited triplet molecules, in competition with similar abstraction by the carbonyl group to form the ketyls.
“…One of the most interesting features of the SCRP is the effect of the relative motion of the two radicals upon the spin dynamics by way of the exchange and the spin dipole-dipole interactions. The fluctuation of the exchange interaction caused by repetitive radical re-encounter that induces so called S-T dephasing [23][24][25][26][27] , can not be expected in the system of a fixed complex structure.…”
Section: ) Discussion Of the Complex Radical Pairmentioning
The photochemical reactions of methylene blue (MB) included in water soluble sulfonated calix[n]arenes (n=4, 6, 8) are studied using a time-resolved ESR method. The CIDEP (chemically induced dynamic electron polarization) spectra show the formation of the complex radical pair composed of the MB monocation radical and calixarene (phenoxyl-type) radical. The lifetime and broadened spectral shape are dependent on the size of the calixarene and are due to the longitudinal and transverse relaxation mainly induced by the tumbling motion of the radical pair with the spin dipole-dipole interaction. The pair dissociates in a few hundreds of nanoseconds in cases of n = 6 and 8.
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