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Michael R. Wasielewski - One of the best experts on this subject based on the ideXlab platform.
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Spin PolarizatIon Transfer from a Photogenerated Radical Ion Pair to a Stable Radical Controlled by Charge RecombinatIon
The journal of physical chemistry. A, 2017Co-Authors: Noah E. Horwitz, Brian T. Phelan, Jordan N. Nelson, Catherine M. Mauck, Matthew D. Krzyaniak, Michael R. WasielewskiAbstract:PhotoexcitatIon of electron donor–acceptor molecules frequently produces Radical Ion pairs with well-defined initial spin-polarized states that have attracted significant interest for spintronics. Transfer of this initial spin polarizatIon to a stable Radical is predicted to depend on the rates of the Radical Ion pair recombinatIon reactIons, but this predictIon has not been tested experimentally. In this study, a stable Radical/electron donor/chromophore/electron acceptor molecule, BDPA•–mPD–ANI–NDI, where BDPA• is α,γ-bisdiphenylene-β-phenylallyl, mPD is m-phenylenediamine, ANI is 4-aminonaphthalene-1,8-dicarboximide, and NDI is naphthalene-1,4:5,8-bis(dicarboximide), was synthesized. PhotoexcitatIon of ANI produces the triRadical BDPA•–mPD+•–ANI–NDI–• in which the mPD+•–ANI–NDI–• Radical Ion pair is spin coupled to the BDPA• stable Radical. BDPA•–mPD+•–ANI–NDI–• and its counterpart lacking the stable Radical are found to exhibit spin-selective charge recombinatIon in which the triplet Radical Ion pair ...
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structure and dynamics of photogenerated triplet Radical Ion pairs in dna hairpin conjugates with anthraquinone end caps
Journal of the American Chemical Society, 2012Co-Authors: Raanan Carmieli, Yasuhiro Kobori, Amanda L Smeigh, Sarah Mickley M Conron, Arun K Thazhathveetil, Masaaki Fuki, Frederick D Lewis, Michael R. WasielewskiAbstract:A series of DNA hairpins (AqGn) possessing a tethered anthraquinone (Aq) end-capping group were synthesized in which the distance between the Aq and a guanine-cytosine (G-C) base pair was systematically varied by changing the number (n – 1) of adenine-thymine (A-T) base pairs between them. The photophysics and photochemistry of these hairpins were investigated using nanosecond transient absorptIon and time-resolved electron paramagnetic resonance (TREPR) spectroscopy. Upon photoexcitatIon, 1*Aq undergoes rapid intersystem crossing to yield 3*Aq, which is capable of oxidizing purine nucleobases resulting in the formatIon of 3(Aq–•Gn+•). All 3(Aq–•Gn+•) Radical Ion pairs exhibit asymmetric TREPR spectra with an electron spin polarizatIon phase pattern of absorptIon and enhanced emissIon (A/E) due to their different triplet spin sublevel populatIons, which are derived from the corresponding non-Boltzmann spin sublevel populatIons of the 3*Aq precursor. The TREPR spectra of the 3(Aq–•Gn+•) Radical Ion pairs d...
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intersystem crossing involving strongly spin exchange coupled Radical Ion pairs in donor bridge acceptor molecules
Journal of Physical Chemistry A, 2012Co-Authors: Michael T Colvin, Annie Butler Ricks, Amy M Scott, Michael R. WasielewskiAbstract:Intersystem crossing involving photogenerated strongly spin exchange-coupled Radical Ion pairs in a series of donor–bridge–acceptor molecules was examined. These molecules have a 3,5-dimethyl-4-(9-anthracenyl)-julolidine (DMJ–An) donor either connected directly or connected by a phenyl bridge (Ph), to pyromellitimide (PI), 1 and 2, respectively, or naphthalene-1,8:4,5-bis(dicarboximide) (NI) acceptors, 3 and 4, respectively. Femtosecond transient optical absorptIon spectroscopy shows that photodriven charge separatIon produces DMJ+•–PI–• or DMJ+•–NI–• quantitatively in 1–4 (τCS ≤ 10 ps), and that charge recombinatIon occurs with τCR = 268 and 158 ps for 1 and 3, respectively, and with τCR = 2.6 and 10 ns for 2 and 4, respectively. Magnetic field effects (MFEs) on the neutral triplet state yield produced by charge recombinatIon were used to measure the exchange coupling (2J) between DMJ+• and PI–• or NI–•, giving 2J > 600 mT for 1–3 and 2J = 170 mT for 4. Time-resolved electron paramagnetic resonance (TREP...
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direct observatIon of the preference of hole transfer over electron transfer for Radical Ion pair recombinatIon in donor bridge acceptor molecules
Journal of the American Chemical Society, 2008Co-Authors: Zachary E X Dance, David W Mccamant, Michael J Ahrens, Mark A Ratner, Annie Butler Ricks, Amy M Vega, Michael R. WasielewskiAbstract:Understanding how the electronic structures of electron donor−bridge−acceptor (D−B−A) molecules influence the lifetimes of Radical Ion pairs (RPs) photogenerated within them (D+•−B−A-•) is critical to designing and developing molecular systems for solar energy conversIon. A general questIon that often arises is whether the HOMOs or LUMOs of D, B, and A within D+•−B−A-• are primarily involved in charge recombinatIon. We have developed a new series of D−B−A molecules consisting of a 3,5-dimethyl-4-(9-anthracenyl)julolidine (DMJ-An) electron donor linked to a naphthalene-1,8:4,5-bis(dicarboximide) (NI) acceptor via a series of Phn oligomers, where n = 1−4, to give DMJ-An-Phn-NI. The photoexcited charge transfer state of DMJ-An acts as a high-potential photoreductant to rapidly and nearly quantitatively transfer an electron across the Phn bridge to produce a spin-coherent singlet RP 1(DMJ+•-An-Phn-NI-•). Subsequent Radical pair intersystem crossing yields 3(DMJ+•-An-Phn-NI-•). Charge recombinatIon within the ...
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time resolved epr studies of photogenerated Radical Ion pairs separated by p phenylene oligomers and of triplet states resulting from charge recombinatIon
Journal of Physical Chemistry B, 2006Co-Authors: Zachary E X Dance, David W Mccamant, Michael J Ahrens, Mark A Ratner, Michael R. WasielewskiAbstract:PhotoexcitatIon of a series of donor−bridge−acceptor (D−B−A) systems, where D = phenothiazine (PTZ), B = p-phenylene (Phn), n = 1−5, and A = perylene-3,4:9,10-bis(dicarboximide) (PDI) results in rapid electron transfer to produce 1(PTZ+•−Phn−PDI-•). Time-resolved EPR (TREPR) studies of the photogenerated Radical pairs (RPs) show that above 150 K, when n = 2−5, the Radical pair−intersystem crossing mechanism (RP−ISC) produces spin-correlated Radical Ion pairs having electron spin polarizatIon patterns indicating that the spin−spin exchange interactIon in the Radical Ion pair is positive, 2J > 0, and is temperature dependent. This temperature dependence is most likely due to structural changes of the p-phenylene bridge. Charge recombinatIon in the RPs generates PTZ−Phn−3*PDI, which exhibits a spin-polarized signal similar to that observed in photosynthetic reactIon-center proteins and some biomimetic systems. At temperatures below 150 K and/or at shorter donor−acceptor distances, e.g., when n = 1, PTZ−Phn−3...
Irina G Irtegova - One of the best experts on this subject based on the ideXlab platform.
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bis toluene chromium i 1 2 5 thiadiazolo 3 4 c 1 2 5 thiadiazolidyl and 1 2 5 thiadiazolo 3 4 b pyrazinidyl new heterospin s1 s2 1 2 Radical Ion salts
Inorganic Chemistry, 2013Co-Authors: Nikolay A Semenov, Nikolay A Pushkarevsky, Elizaveta A Suturina, Elena A Chulanova, Natalia V Kuratieva, Artem S Bogomyakov, Irina G IrtegovaAbstract:Bis(toluene)chromium(0), Cr0(η6-C7H8)2 (3), readily reduced [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazole (1) and [1,2,5]thiadiazolo[3,4-b]pyrazine (2) in a tetrahydrofuran solvent with the formatIon of heterospin, S1 = S2 = 1/2, Radical-Ion salts [3]+[1]− (4) and [3]+[2]− (5) isolated in high yields. The salts 4 and 5 were characterized by single-crystal X-ray diffractIon (XRD), solutIon and solid-state electron paramagnetic resonance, and magnetic susceptibility measurements in the temperature range 2–300 K. Despite the formal similarity of the salts, their crystal structures were very different and, in contrast to 4, in 5 anIons were disordered. For the XRD structures of the salts, parameters of the Heisenberg spin Hamiltonian were calculated using the CASSCF/NEVPT2 and broken-symmetry density functIonal theory approaches, and the complex magnetic motifs featuring the dominance of antiferromagnetic (AF) interactIons were revealed. The experimental χT temperature dependences of the salts were simulated us...
Elena A Chulanova - One of the best experts on this subject based on the ideXlab platform.
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bis toluene chromium i 1 2 5 thiadiazolo 3 4 c 1 2 5 thiadiazolidyl and 1 2 5 thiadiazolo 3 4 b pyrazinidyl new heterospin s1 s2 1 2 Radical Ion salts
Inorganic Chemistry, 2013Co-Authors: Nikolay A Semenov, Nikolay A Pushkarevsky, Elizaveta A Suturina, Elena A Chulanova, Natalia V Kuratieva, Artem S Bogomyakov, Irina G IrtegovaAbstract:Bis(toluene)chromium(0), Cr0(η6-C7H8)2 (3), readily reduced [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazole (1) and [1,2,5]thiadiazolo[3,4-b]pyrazine (2) in a tetrahydrofuran solvent with the formatIon of heterospin, S1 = S2 = 1/2, Radical-Ion salts [3]+[1]− (4) and [3]+[2]− (5) isolated in high yields. The salts 4 and 5 were characterized by single-crystal X-ray diffractIon (XRD), solutIon and solid-state electron paramagnetic resonance, and magnetic susceptibility measurements in the temperature range 2–300 K. Despite the formal similarity of the salts, their crystal structures were very different and, in contrast to 4, in 5 anIons were disordered. For the XRD structures of the salts, parameters of the Heisenberg spin Hamiltonian were calculated using the CASSCF/NEVPT2 and broken-symmetry density functIonal theory approaches, and the complex magnetic motifs featuring the dominance of antiferromagnetic (AF) interactIons were revealed. The experimental χT temperature dependences of the salts were simulated us...
Elizaveta A Suturina - One of the best experts on this subject based on the ideXlab platform.
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bis toluene chromium i 1 2 5 thiadiazolo 3 4 c 1 2 5 thiadiazolidyl and 1 2 5 thiadiazolo 3 4 b pyrazinidyl new heterospin s1 s2 1 2 Radical Ion salts
Inorganic Chemistry, 2013Co-Authors: Nikolay A Semenov, Nikolay A Pushkarevsky, Elizaveta A Suturina, Elena A Chulanova, Natalia V Kuratieva, Artem S Bogomyakov, Irina G IrtegovaAbstract:Bis(toluene)chromium(0), Cr0(η6-C7H8)2 (3), readily reduced [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazole (1) and [1,2,5]thiadiazolo[3,4-b]pyrazine (2) in a tetrahydrofuran solvent with the formatIon of heterospin, S1 = S2 = 1/2, Radical-Ion salts [3]+[1]− (4) and [3]+[2]− (5) isolated in high yields. The salts 4 and 5 were characterized by single-crystal X-ray diffractIon (XRD), solutIon and solid-state electron paramagnetic resonance, and magnetic susceptibility measurements in the temperature range 2–300 K. Despite the formal similarity of the salts, their crystal structures were very different and, in contrast to 4, in 5 anIons were disordered. For the XRD structures of the salts, parameters of the Heisenberg spin Hamiltonian were calculated using the CASSCF/NEVPT2 and broken-symmetry density functIonal theory approaches, and the complex magnetic motifs featuring the dominance of antiferromagnetic (AF) interactIons were revealed. The experimental χT temperature dependences of the salts were simulated us...
Nikolay A Pushkarevsky - One of the best experts on this subject based on the ideXlab platform.
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bis toluene chromium i 1 2 5 thiadiazolo 3 4 c 1 2 5 thiadiazolidyl and 1 2 5 thiadiazolo 3 4 b pyrazinidyl new heterospin s1 s2 1 2 Radical Ion salts
Inorganic Chemistry, 2013Co-Authors: Nikolay A Semenov, Nikolay A Pushkarevsky, Elizaveta A Suturina, Elena A Chulanova, Natalia V Kuratieva, Artem S Bogomyakov, Irina G IrtegovaAbstract:Bis(toluene)chromium(0), Cr0(η6-C7H8)2 (3), readily reduced [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazole (1) and [1,2,5]thiadiazolo[3,4-b]pyrazine (2) in a tetrahydrofuran solvent with the formatIon of heterospin, S1 = S2 = 1/2, Radical-Ion salts [3]+[1]− (4) and [3]+[2]− (5) isolated in high yields. The salts 4 and 5 were characterized by single-crystal X-ray diffractIon (XRD), solutIon and solid-state electron paramagnetic resonance, and magnetic susceptibility measurements in the temperature range 2–300 K. Despite the formal similarity of the salts, their crystal structures were very different and, in contrast to 4, in 5 anIons were disordered. For the XRD structures of the salts, parameters of the Heisenberg spin Hamiltonian were calculated using the CASSCF/NEVPT2 and broken-symmetry density functIonal theory approaches, and the complex magnetic motifs featuring the dominance of antiferromagnetic (AF) interactIons were revealed. The experimental χT temperature dependences of the salts were simulated us...