Chemically induced dynamic electron polarization. II. A general theory for radicals produced by photochemical reactions of excited triplet carbonyl compounds

Wong, S. K.; Hutchinson, D. A. W.; Wan, J. K. S.

doi:10.1063/1.1679355

Cited by 157 publications

(42 citation statements)

References 26 publications

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“…Although in general, 0i contains nine different elements for each triplet species, in the case of CW detection, only matrix elements, which correspond to the coherence generated between levels 1 and 2 of the triplet and levels 2 and 3 of the triplet (under high magnetic field), are important for the line shape calculation (5). Thus, for the case of thermal triplets, 0i can be taken as: ͪ [24] which means that the population difference between levels 1 and 2 is (almost) equal to the population difference between levels 2 and 3. For photoexcited triplets, with spin polarization, the population difference between the levels is far from being equal.…”

Section: Triplet Line Shape Simulationmentioning

confidence: 99%

“…Apart from its relative simplicity, the advantage of the method presented here is that more involved and generalized cases of exchange processes, with or without rotation, can be treated accordingly. In the most generalized case, each species may have its own ZFS parameters (D and E), anisotropic spin relaxation times (T 1x , T 1y , T 1z , T 2x , T 2y , T 2z ), and anisotropic selective levels' population (A x , A y , A z to the triplet X, Y, and Z levels, respectively) (24). In addition, each species may have its own orientation in the magnetic field.…”

Section: Triplet Line Shape Simulationmentioning

confidence: 99%

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Triplet line shape simulation in continuous wave electron paramagnetic resonance experiments

Blank¹,

Levanon²

2005

Concepts Magn. Reson.

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ABSTRACT:We present a simple yet powerful method of simulating continuous wave electron spin resonance line shape of triplets in frozen and liquid solutions. The analysis enables one to consider cases such as immobilized triplets with random distribution, anisotropic slow and fast rotation of the triplet molecules, exchange between triplets with different Hamiltonians, anisotropic relaxation rates, and triplets with non-Boltzmann population distribution of the spin levels. Theoretical basis for the method is provided, along with several examples of simulated and experimental spectra for various physical conditions. A short "Matlab" routine, which can be used in the numerical spectra simulation, is given in the Appendix.

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Section: Triplet Line Shape Simulationmentioning

confidence: 99%

Section: Triplet Line Shape Simulationmentioning

confidence: 99%

Triplet line shape simulation in continuous wave electron paramagnetic resonance experiments

Blank¹,

Levanon²

2005

Concepts Magn. Reson.

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“…In our analysis we neglect any decay between the sublevels and consider separate decay rates k x;y;z from each sublevel to the singlet ground state. The decay rates and the initial populations n x;y;z are each properties of the triplet eigenstates at zero applied magnetic field (T x;y;z ), and so can be used to determine the resulting decay rates and populations at any applied magnetic field by writing the in-field eigenstates (T þ;0;À ) in the appropriate basis [21]. Using this approach, we simultaneously fit the decay traces of flash delay (h À T À =2 À À -echo) and inversion recovery (h À t À À T À =2 À À -echo) experiments at four fields, using one set of parameters: p x :p y :p z ¼ 0:46:0:54:0:00 and x ¼ ð0:50 AE 0:02Þ ms, y ¼ ð0:58 AE 0:02Þ ms, z ¼ ð0:020 AE 0:003Þ ms (20 K), where i ¼ 1=k i .…”

Section: Fig 1 (Color Online) (A)mentioning

confidence: 99%

Entangling Remote Nuclear Spins Linked by a Chromophore

et al. 2010

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Molecular nanostructures may constitute the fabric of future quantum technologies, if their degrees of freedom can be fully harnessed. Ideally one might use nuclear spins as low-decoherence qubits and optical excitations for fast controllable interactions. Here, we present a method for entangling two nuclear spins through their mutual coupling to a transient optically excited electron spin, and investigate its feasibility through density-functional theory and experiments on a test molecule. From our calculations we identify the specific molecular properties that permit high entangling power gates under simple optical and microwave pulses; synthesis of such molecules is possible with established techniques. DOI: 10.1103/PhysRevLett.104.200501 PACS numbers: 03.67.Bg, 03.67.Lx, 31.15.EÀ, 33.40.+f Molecules are promising building blocks for quantum technologies, due to their reproducible nature and ability to self-assemble into complex structures. However, the need to control interactions between adjacent qubits represents a key challenge [1][2][3][4]. We here describe a method for optical control of a nuclear spin-spin interaction that presents several advantages over conventional NMR quantum processors: the spin-spin interaction can be switched, the gates are faster, and the larger energy transitions facilitate polarization transfer onto the nuclear spins. After explaining the theory behind our method, we present an experimental study of a test molecule, and show with density-functional theory that an entangling gate could be achieved.We consider two nuclear spin qubits labeled n and n 0 and one mediator e. The mediator possesses a paramagnetic excited state jei with spin one character and a diamagnetic, spinless ground state j0i. The two nuclear qubits do not interact with each other directly, but both couple to the excitation via an isotropic hyperfine (HF) coupling with generally unequal strengths A and A 0 , see Fig. 1(a). The Hamiltonian in a magnetic field is given by (@ ¼ 1):where S z;i and S i are the Pauli spin operators and ! i denotes the respective Zeeman splittings (i ¼ n, n 0 , e). D is the zero-field-splitting (ZFS). ! 0 denotes the optical frequency corresponding to the creation energy of the excitation. Let us first analyze the case of a symmetric (homonuclear) system with ! n ¼ ! n 0 and A ¼ A 0 . Using degenerate perturbation theory and assuming that the electronic Zeeman splitting is much larger than that of the nuclei, ! n ( ! e and the ZFS, D ( ! e , we obtain an effective Hamiltonian by approximating H sym : ¼ hejHjei; thus,where V ¼ ðjc 1 ijc 2 i Á Á Á jc 12 iÞ is the matrix of the approximate eigenvectors up to first order and the E i (i ¼ 1; . . . ; 12) are the eigenenergies up to second order. This reveals that the time evolution of the entire system can be

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“…In fact, these triplets appear asa result of the intramolecular nonradiative transitions from the excited singlet state. In the molecular frame these transitions are spin-selective and the triplet states are born with polarized spins (see, e.g., [4][5][6]). …”

Section: Introductionmentioning

confidence: 99%

Time-resolved EPR study of electron spin polarization and spin exchange in mixed solutions of porphyrin stable free radicals

et al. 2003

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The time-resolved electron paramagnetic resonance (EPR) spectra are studied in the temperature range of 110-300 K for two mixed solutions of porphyrins, ZnTPP and H2TPP, in toluene and the stable free radical 2,2,6,6-tetramethyl-l-piperidinyloxyl (TEMPO). The EPR spectra and their kinetic behavior were studied for concentrations of TEMPO vafied in the interval from 0.51 to 7.68 mM, while the porphyrin concentration was fixed as I mM. The EPR spectra of triplet-state porphyrins and free radicals manifest the chemically induced spin polarization. For the relatively short-lived radical-triplet pairs, with the perturbation theory up to the fourth order, the theoretical expressions ate obtained for the triplet and radical spin polarization induced by the enhanced intersystem crossing (ISC) due to the interaction of excited singlet-state porphyrins with free radicals and by the triplet quenching by free radicals. The time-dependent EPR spectra of the t¡ are simulated taking into account the spin-lattice relaxation. Ir is shown that the variation of the triplet EPR spectra shape, when the time of observation increases, arises from the spin-lattiee relaxation kineties. The kinetic behavior of the TEMPO EPR spectrum was simulated on the basis of the kinetie scheme suggested earlier in the literature. The triplet spin-lattice relaxation time, the tate of the ISC and the lifetime of the excited singlet state were estimated by fitting the kinetic curves for the triplet EPR spectra intensity. For the mixed porphyrin-TEMPO solutions, a possible set of the rate constants of important bimolecular proeesses were determined. For this set of parameters, it turns out that the spin polarization transfer has a smaller rate constant than the rate constant of the diffusion collisions of the triplet and radical. It appears that the rate constant of the ISC catalyzed by radieals is relatively high in the solutions close to the melting point of the solvent and in the soft-glassy state. In the triplet porphyrins the initial spin pola¡ induced by the spin-selective ISC was found to exceed the equilibrium spin polarization by up to two orders of magnitude.

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Chemically induced dynamic electron polarization. II. A general theory for radicals produced by photochemical reactions of excited triplet carbonyl compounds

Cited by 157 publications

References 26 publications

Triplet line shape simulation in continuous wave electron paramagnetic resonance experiments

Triplet line shape simulation in continuous wave electron paramagnetic resonance experiments

Entangling Remote Nuclear Spins Linked by a Chromophore

Time-resolved EPR study of electron spin polarization and spin exchange in mixed solutions of porphyrin stable free radicals

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