Photoinduced electron tunneling reactions in chemistry and biology

Zamaraev, K. I.; Khairutdinov, R. F.

doi:10.1007/3-540-55117-4_4

Cited by 12 publications

(19 citation statements)

References 272 publications

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“…Note that in the experiment performed at 253 K within a given time range, the recombination rate exhibits a long-time behavior close to ∼ t –1 , as predicted theoretically for the tunneling recombination of geminate ion pairs in the absence of diffusion (see eq below). This agrees with experiments at very low temperature, when the fluorescence intensity decay from irradiated polyethylenes can be proportional to t –1 even at a time scale of minutes.…”

Section: Results and Discussionsupporting

confidence: 77%

“…The nature of these peculiarities is not clear at this stage. Qualitatively, the discussed positive field effect appears to be similar to that observed in studies of ion pair recombination in low-temperature glasses: turning on the external electric field after the creation of ion pairs results in a transitory increase in recombination fluorescence intensity . Such an electric field effect was explained by the field increasing the tunneling recombination rate for some ion pairs, which otherwise would recombine much later.…”

Section: Results and Discussionsupporting

confidence: 76%

“…In all cases, at t > 20 ns the I ( t ) dependence was of a nonexponential, hyperbolic form that is typical of nonhomogeneous intratrack recombination of RIPs. , As the fluorescence time of the luminophore used was short, about 1 ns, to a first approximation the fluorescence intensity was directly proportional to the RIP recombination rate. Within the limits imposed by the method of single photon counting, that is, with a ∼10% probability of registering a photon after the excitation pulse, the shape of the kinetic curves was found to be independent of the intensity of X-ray irradiation.…”

Section: Results and Discussionmentioning

confidence: 89%

“…The concentration variations had a noticeable effect only on the signal-to-noise ratio in the calculated kinetic curves for the secondary RIP recombination rate after their normalization to the maximum. The mentioned weak dependence of the shape of recombination kinetics on acceptor concentration originated from the universality of asymptotic behavior of such kinetic curves and, consequently, on initial distance distribution in the pairs composed of primary radical cations and dopant radical anions. An increase in electron mobility also weakly affects this distribution at a given electron scavenging radius, and the weak effect of the kinetics on the electron mobility was confirmed by the simulations.…”

Section: Results and Discussionmentioning

confidence: 99%

“…Two other approaches focusing on investigations of charge carrier migration and recombination should be mentioned here. One is based on measurements of the luminescence that appears upon ion recombination. − Another utilizes the detection of radiation-induced conductivity of polymers, ,,, in particular by using time-of-flight measurements, which allow determining the sign of charge carriers as well as their mobility. Typically, these approaches are used to provide data on the energy of charge carriers trapped in polymers, but it is difficult to use these data to identify the charge carriers that contribute to the detected signals.…”

Section: Introductionmentioning

confidence: 99%

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Radiation-Induced Fluorescence from Doped Polyolefins on a Nanosecond Time Scale: Kinetics of the Processes Involving Geminate Radical Ions

2019

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The delayed radiation-induced fluorescence from polyethylene and its alkyl-and fluorine-substituted analogues doped with aromatic luminophores was studied in the time range of 1−1000 ns. Qualitative analysis of the effects of a magnetic field on the fluorescence decay indicated that, in all polyolefins studied, the main portion of the fluorescence observed arose from the recombination of geminate spincorrelated radical ion pairs (RIPs). In the case of polyethylene, this conclusion was supported by observing the effect of an external electric field on the fluorescence decay. It was shown by comparison with the computer simulation of intratrack recombination that the tunneling character of the RIP recombination, which had an asymptotic time dependence of the geminate recombination rate close to t −1 , was typical of most studied polyolefins at temperatures below 273 K in the time range studied. The increase to room temperature and above caused a gradual transition to a regime where the geminate recombination rate was mainly determined by the migration of RIP partners with time dependence close to t −3/2 . The low estimate of the electron transfer distance upon the ion recombination in this regime was about 2 nm. In polyethylenes, exposed to an irradiation of 0.3−0.4 MGy, the role of charge carrier diffusion became hardly noticeable because of the cross-linking of polyethylene chains and the increase in polymer matrix stiffness. Oxygen, dissolved in a polymer doped with aromatic molecules, caused quenching of the recombination luminescence due to electron transfer from the dopant radical anion to the oxygen molecules. At room temperature, typical distances for such electron transfer were estimated to be ∼1.5 nm.

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Section: Results and Discussionsupporting

confidence: 77%

Section: Results and Discussionsupporting

confidence: 76%

Section: Results and Discussionmentioning

confidence: 89%

Section: Results and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Radiation-Induced Fluorescence from Doped Polyolefins on a Nanosecond Time Scale: Kinetics of the Processes Involving Geminate Radical Ions

2019

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ChemInform Abstract: Photoinduced Electron Tunneling Reactions in Chemistry and Biology

Zamaraev

Khairutdinov

1993

ChemInform

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Photochemical and photophysical properties ofmeso-tetraferrocenylporphyrin. Quenching ofmeso-tetraphenylporphyrin by ferrocene

et al. 1999

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hA. N. Nesmeyanov Institute of Organoelement Compounds. Russian Academy of Sciences, 28 uL Vavilova, 117813 Moscow. Russian Federation. Fax: + 7 (095) 135 5085 h was found that the quantum yield of the fluorescence of meso-tetraferrocenylporphyrin Key words: meso-tetraferrocenylporphyrin, meso-tetraphenylporphyrin, ferrocene, fluorescence, nanosecond laser photolysis.The photochemical and photophysical properties of porphyrins have been studied in detail in development of photocatalytic processes and studies of electron transfer reactions in biological and artificial systems. I-6 Great attention was paid to porphyrin dyads and triads, molecular systems in which the tetrapyrrole cycle is covalently linked through a molecular bridge or without it with electron donors or acceptors such as viologen, quinones, C60, etc. 7-18 These molecularly organized systems imitate directed electron transfer in biological objects and are of interest for photocatalysis and devices that convert light energy into electric energy.New porphyrin molecules that can be considered as porphyrin dyads in which the tetrapyrrole cycle is covalently linked in the meso-position with metallocenes, in particular, with fcrrocene (FcH), directly tg.z~ or through various bridges, CHa--CHa, 21 trans-CH=CH 21 and eis-CH=CH, zl and -~O-were recently synthesized, z2,z3 A high quantum yield ofcha~e separation and efficient light conversion in photogalvanic cells were observed for the porphyrin linked with Fc through the phenoxyl bridge. ~ In this work, we studied the photochemical and photophysical properties of porphine covalently linked in meso-positions with four Fc groups, meso-tetraferrocenylporphyrin (TFcP). Quenching of singlet-and triplet-excited meso-tetraphenylporphyrin (TPP) by FcH was also studied to reveal the character of the interaction of excited porphine with Fc groups. ExperimentalThe following reagents were used: acetonitrile and toluene (Fluka, for HPLC analysis) as solvents, TPP (Fluka, without TFcP TPP additional purification), and ferrocene (Fluka). The latter was recrystallized four times from methanol lbllowed by vacuum sublimation. Synthesis of TFcP has been described in detail in previous works. 19"20

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Photoinduced electron tunneling reactions in chemistry and biology

Cited by 12 publications

References 272 publications

Radiation-Induced Fluorescence from Doped Polyolefins on a Nanosecond Time Scale: Kinetics of the Processes Involving Geminate Radical Ions

Radiation-Induced Fluorescence from Doped Polyolefins on a Nanosecond Time Scale: Kinetics of the Processes Involving Geminate Radical Ions

ChemInform Abstract: Photoinduced Electron Tunneling Reactions in Chemistry and Biology

Photochemical and photophysical properties ofmeso-tetraferrocenylporphyrin. Quenching ofmeso-tetraphenylporphyrin by ferrocene

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