Dynamic Spin Polarization Research Articles

Intrinsic Enhancement Factors of the Spin−Orbit Coupling Mechanism Polarization in the Duroquinone−N,N-Dimethylaniline Derivative Systems

Dynamics of the electron spin polarization of the quinone anion radical generated from the photoinduced electron transfer between duroquinone (DQ) and N,N-dimethylaniline (DMA) as well as its p-halogen substituents (4XDMA) has been investigated by using transient absorption and FTEPR spectroscopies. The radical yield decreased with increasing atomic number of the halogen in the donor. The intrinsic enhancement factors of net absorptive polarization due to the spin−orbit coupling mechanism (SOCM) of VSOCM = 2, 17, and 25 were determined in the unit of thermal equilibrium polarization at room temperature for the DQ-4ClDMA, DQ-4BrDMA, and DQ-4IDMA systems, respectively. The net absorptive spin polarization observed has been discussed in terms of SOC interaction of the triplet contact radical ion pair (CRIP) state with the ground state, which is coupled with the singlet CRIP states in the solvent coordinate.

From regular to erratic quantum dynamics in long spin 1/2 chains with an XY Hamiltonian

The dynamics of spin polarization driven by the XY Hamiltonian of a linear spin 1/2 chain of arbitrary length N was studied analytically and numerically. For an initial state with polarization localized on a single spin, I jz , the dimension of the accessible Liouville subspace grows with N 2. The polarization propagates along the chain in the form of spin-wave packets that gradually split into sub-packets bouncing back and forth at the ends. The initially regular appearance turns at longer times into an erratic behavior due to the complex interference of the spin-wave packets. Even for large N and long times the density operator exhibits large-amplitude fluctuations about its long-term average, which is non-ergodic in the sense that it is dependent on the initial conditions of the dynamics.

Spin Identification of Polyionic High-Spin Aryl-Based Heteroatomic Systems by 2D Electron Spin Transient Nutation (2D-ESTN) Spectroscopy

Molecular design, generation, and spin identification of polyionic high spins with heteroatomic π-conjugation are described. The molecular design was based upon the π-topological pseudo-degeneracy of HOMO's for high-spin polycations and LUMO's for high-spin polyanions. The pseudo-degeneracy originates in heteroatomic perturbation and high spin preference in their ground state is driven by meta- or 1,3,5-connectivity of heteroatomic sites giving rise to additive dynamic spin polarization. Polyionic high spins were generated by chemical oxidation or reduction in solution. Thus, the polyions were observed in a rigid glass solution containing reaction mixture. For such complex spin systems their reliable spin identification is essential and, therefore, we employed field-swept 2D electron spin transient nutation (2D-ESTN) spectroscopy. In this work, we have developed such a 2D-ESTN spectroscopy as deserves to enhance spectral resolution in complex spin mixture of non-oriented systems. An unequivocal and facile spin identification of the polyions was carried out, demonstrating that the topological version of the molecular design has been established for polyionic high-spin preference in heteroatomic π-conjugation. It has turned out that the 2D-ESTN spectroscopy is feasible for high spin mixture of any kinds and provides us with direct experimental discrimination between high spins of different spin multiplicities.

Syntheses of Model Oligomers for Polyionic Organic Ferromagnetics and their High-Spin Characterization by FT Pulsed Esr/Electron Spin Transient Nutation (Estn) Spectroscopy as a Novel Experimental Technique

This paper deals with syntheses and unequivocal spin identification of prototypical model oligomers for the π-topological version of an approach to purely organic polyionic polymer ferromagnets, emphasizing that molecular design exploits the topological super pseudo-degeneracy of π-bonding and π-antibonding molecular orbitals (π-HOMOs and π-LUMOs) appearing close to zero energy in heteroatomic π-conjugated organic systems, for polycationic and polyanionic organic polymeric high spins, respectively. The oxidation and reduction states of the oligomers designed according to the topological approach are expected to undergo dynamic spin polarization, leading to high-spin ground states for both polycationic and polyanionic model oligomers. One-dimensional and two-dimensional star-burst polycationic model oligomers with heteroatoms participating in π-conjugation were designed and synthesized. Their electronic high-spin ground states have been identified by means of Two-Dimensional Electron Spin Transient Nutation (2D-ESTN) spectroscopy based on an FT pulsed ESR technique to which recently we have exerted ourselves in order to obtain technical advances in molecular spin science underlying the research field of molecule-based magntics. In this study, the polyketone-based polyanionic high-spin species have been generated also by a dry process, i.e., electron doping by γ-irradiation in organic glasses.

Molecular Designs for Polyionic Organic Ferromagnetics in Terms of Band Structure Calculation/ Crystal Orbital Approach; Exploitation of Topological Super Pseudo-Degeneracy of π-Bco's and π-Abco's with Hetero-Atomic Perturbation

One of the highlighted conceptual advances in organic magnetics and molecule-based magnetism has been that the use of topological-symmetry requirement in the π-electron network of “open-shell homoatomic neutral hydrocarbon systems” gives rise to the unlimited number of the degeneracy in non-bonding molecular orbitals (coined as topological degeneracy). This paper deals with the π-topological version of an approach to purely organic polyionic polymer ferromagnets, emphasizing that molecular design exploits the topological super pseudo-degeneracy of π-bonding and π-antibonding crystal orbitals (π-BCOs and π-ABCOs; it-bands) appearing close to zero energy in heteroatomic π-conjugated organic systems, for polycationic and polyanionic organic polymer ferromagnets, respectively. The appearance of the BCOs and ABCOs close to zero energy as well as their pseudo-degeneracy is due to heteroatomic perturbation. Their super degeneracy arises from the topological nature of the π-conjugated electron network of the elaborate molecular design. Oxidation and reduction states of polymers designed according to the topological approach are expected to undergo the additive operation of dynamic spin polarization, leading to high-spin ground states for polycationic and polyanionic model polymers, respectively. One-dimensional and two-dimensional star-burst model oligomers with heteroatoms in π-conjugation were designed as prototypical examples. Also, description of ferromagnetic or antiferromagnetic spin alignment depending on the topological symmetry in π-conjugation is given in terms of dynamic spin polarization.

X- and W-Band Time-Resolved Electron Paramagnetic Resonance Studies on Radical-Excited Triplet Pairs between Metalloporphyrins and Axial-Ligating Nitroxide Radicals

A chemically induced dynamic electron spin polarization (CIDEP) study has been accomplished on radical-excited triplet pairs (RTP) in systems of metalloporphyrins, MgTPP, ZnTPP, and ZnOEP, and pyridine-substituted nitronyl nitroxide radicals, nit-R (R = o-py, m-py, and p-py), by X- (9.5 GHz) and W-band (95 GHz) time-resolved electron paramagnetic resonance (TREPR) in solution. Axial-ligations between the porphyrins and the radicals were ascertained from visible absorption spectra except for the nit-o-py system. The TREPR spectra were composed of two signals, which were assigned to those of the ground (D0) state of the radical and the excited quartet (Q1) state of the RTP. These components showed two kinds of CIDEPs in different time regions. The polarizations of the Q1 state were attributed to radical−triplet pair mechanisms (RTPMs) with singlet and triplet precursors. In the nit-p-py and the nit-m-py systems, the polarizations of the radical were generated via an electron spin polarization transfer (ESPT...

Electronic Structures of Ions ofm-Phenylenebis(Phenylmethylene). I - UHF Studies -

We study the electronic states of monocation and monoanion of m -phenylenebis (phenylmethylene) in the unrestricted Hartree-Fock (UHF) approximation. We use the model in which the intraatomic Coulomb and exchange interactions on carbenes and the transfer and Coulomb interactions between n and π electrons are added to the Pariser-Parr-Pople (PPP) model. It has the quintet ground state in the neutral state, due to the dynamic spin polarization (DSP) in the π system and the exchange interaction between n and π electrons on carbene sites. The bond angles on carbenes are optimized with the Hellmann-Feynmann condition showing that the lattice polaron effect on ionization is small below 2°. If the ions are planer, they have the doublet ground state, but if we take into account the twisting around the carbene bonds due to steric hindrance, they have the quartet ground state, indicating importance of the n-π mixing. The UHF ground state with S z =3/ 2 is of broken symmetry. The injected charge is localized on a ca...

Electronic Structures of Ions ofm-Phenylenebis (Phenylmethylene). II - The Electron Correlation Effects -

m -Phenylenebis (phenylmethylene) ( m -PBPM) has the quintet ground state in the neutral state, due to the dynamic spin polarization (DSP) in the π system and exchange interaction between n and π electrons on carbenes. The experimental results by the ESR show that both monocation and monoanion of m -PBPM have the quartet ground state. We calculate the electronic structures of the ions with the unrestricted Hartree-Fock (UHF) and resonating Hartree-Fock (Res HF) methods. We use the model that includes only n and π electrons developed in a previous paper. The broken spatial and spin symmetries of the UHF solutions are restored by the Res HF calculations of electron correlation effects. In the UHF approximation, the doped charge is always localized on a carbene and the adjacent phenylenes as a spin density wave (SDW) polaron. The n spins on the right and left carbenes are parallel and antiparallel in the quartet and doublet states, respectively. Due to this fact, the stabilization by the quantum motion of th...

Molecular design for polyionic organic ferromagnets and syntheses of model oligomers; Exploitation of topological superdegeneracy of π-BCO's and π-ABCO's, and high spin characterization by FT pulsed ESR/ESTN spectroscopy as a novel experimental technique

The conceptual proposals of organic magnetism/molecule-based magnetism in terms of non-charged open-shell units were made as early as 1960's. One of the highlighted advances has been that the use of topological-symmetry requirement in the electron network of it-conjugated homoatomic neutral hydrocarbon systems gives rise to the unlimited number of the degeneracy in non-bonding molecular orbitals (coined as topological degeneracy). This paper deals with the π-topological version of an approach to purely organic polyionic polymer ferromagnets, emphasizing that molecular design exploits the topological pseudo superdegeneracy of π-bonding and -antibonding crystal orbitals (π-BCOs and π-ABCOs; π-bands) appearing close to zero energy in heteroatomic π-conjugated organic systems, for pofycationic and poryanionic organic polymer ferromagnets, respectively. The appearance of the BCOs and ABCOs close to zero energy as well as their pseudo degeneracy is due to heteroperturbation. Their superdegeneracy arises from the topological nature of the electron network of π-conjugation. Oxidation and reduction states of polymers designed according to the topological approach are expected to undergo dynamic spin polarization, leading to high-spin ground states for porycationic and poryanionic model porymers, respectively. One-dimensional and two-dimensional star-burst model oligomers with heteroatoms in π-conjugation were designed and synthesized Their electronic high-spin ground states have been identified by means of Electron Spin Transient Nutation (ESTN) spectroscopy based on FT pulsed ESR technique to which recently we have exerted ourselves in order to obtain technical advances in molecular spin science underlying the research field of molecule-based magnetism. Most of the poryionic high-spin species have been generated by wet processes, i.e., chemical reaction in solution. In this study, the poryketone-based poryanionic high-spin species have been generated also by a dry process, i.e., electron attachment via γ-irradiation in organic glasses.

Time‐Resolved (CW) Electron Paramagnetic Resonance Spectroscopy: An Overview of the Technique and Its Use in Organic Photochemistry

Abstract— Steady‐state and time‐resolved electron paramagnetic resonance (TREPR) experiments are described. Comparison of the TREPR continuous wave method to other time domain EPR techniques such as Fourier transform EPR (FT‐EPR) is made, and the advantages and disadvantages of each are presented. The role played by several mechanisms of chemically induced dynamic electron spin polarization (CIDEP) in the appearance of the spectra is explained. The advantages of using higher frequency spectrometers than the standard X‐band (9.5 GHz) are presented and discussed. Examples are presented that are relevant to organic photochemistry and electron donor‐acceptor chemistry. The use of TREPR to study polymer photodegradation, polymer chain dynamics, free radical initiator chemistry and biradical spin exchange interactions is described. Emphasis is placed on magnetic field effects studied by multiple frequency TREPR in these systems. Finally, several future directions in the field are discussed in terms of new developments in microwave and magnetic field technology.

Spin polarization of photoelectrons from zinc atoms in the autoionization region

We have measured the energy dependence of the dynamical spin-polarization parameters for photoelectrons from zinc atoms in the wavelength region from 100 nm to 115 nm. The pronounced structure near the resonances found in previously measured absorption spectra also occurs in the spin-polarization parameters. From the experimental results the dipole transition matrix elements including the relative phase shift difference have been determined. The data are also compared with an existing R-matrix calculation and a new calculation employing semi-empirical Slater - Condon parameters.

Ferromagnetic intermolecular interaction of the cation radical of m-N-methylpyridinium nitronyl nitroxide. A CASSCF study

Semi-empirical APUHF and ab initio UNO CASSCF/4-31G calculations have been carried out for the dimer of m-N-methylpyridinium nitronyl nitroxide cation ( m-MPYNN +) extracted from its experimental crystal structure in order to elucidate the origin of the large ferromagnetic effective exchange integral | J ab|. It is found that the sign of the calculated J ab is positive, and its magnitudes are 6.51 and 3.96 cm −1 by these methods, which correspond to about 80 and 50% of the experimental value, respectively. The dynamic spin polarization plays an important role in determining the sign of J ab, whereas the short intermolecular contact induced by the Coulombic attraction is reponsible for the large J ab. Implications of the calculated results are discussed in relation to the possibilities of high- T c organic ferromagnets and organic helimagnets.

Photodegradation of Alternating p-tert-Butylstyrenyl- and exo-Norbornyl-CO Copolymers Studied by Multiple-Frequency Time-Resolved Electron Paramagnetic Resonance Spectroscopy

The photodegradation of two alternating R-CO copolymers (R= p-tert-butylstyrenyl and exo-norbornyl) was studied using time-resolved EPR spectroscopy at two different frequencies, X-band (9.5 GHz) and Q-band (35.1 GHz), and by product analysis. For the tert-butylstyrenyl-CO copolymer the EPR spectra displayed strong chemically induced dynamic spin polarization (CIDEP) expected fort triplet-born radical pairs from the Norrish I α-cleavage reaction. Simulation of the spectra allowed unambiguous assignment of the radicals present as early as 200 ns after the laser flash

Theoretical Approaches to Molecular Magnetisms: Through-Bond Couplings Between Triplet Carbenes and Related Species

Abstract Ab initio post Hartree-Fock calculations were carried out for polyradical species formed by the through-bond couplings between organic radical groups such as triplet carbenes. Detailed numerical results indicate that the dynamic spin polarization (SP) rules proposed previously are applicable to qualitative predictions of the ground spin states of these species. On the other hand, the spin derealization (SD) mechanism is operative in the case of polyradicals linked with hetero atoms such as oxygen and nitrogen atoms. The ionized states of polycarbenes and polyenes are also investigated in relation to possibilities of organic magnetic conductors. Computational results are compatible with experimental results available.

Design of Donor Oligomers to Produce Parallel Spins Upon Charge Transfer

Abstract We design covalently bonded dimers of donor molecules to give parallel spin coupling owing to the dynamic spin polarization of linking bonds if the donors become cation radicals upon charge transfer. We show the triplet nature of the ground state of the dications of the dimers by UHF calculations in the PPP model.

Viscosity dependence of chemically induced dynamic electron spin polarization generated by the radical-triplet pair mechanism

Chemically induced dynamic electron spin polarization generated through the interaction between the excited singlet and triplet molecules with nitroxide radicals is measured in several solvents and micellar solutions. The relative intensity of net polarization is more enhanced than hyperfine-dependent polarization in highly viscous solvents and micellar solutions. The enhancement of net polarization is interpreted by the mixing of |Q-3/2> and |D1/2> states in the radical-triplet pair mechanism (RTPM) due to the slack motion of radical-triplet pairs. These results verify that net and multiplet polarizations are independently generated in RTPM

Time development of Electron Spin Polarization in magnetically coupled, spin correlated radical pairs

A general description of the Electron Spin Polarization (ESP) dynamics is presented for photoinduced correlated radical ion spin pairs with particular significance to the respective primary processes in photosynthetic reaction centers. It applies to different coupling situations for the pair spins. The main emphasis is given to the role of coherence effects. It is predicted that a regular direct detection EPR experiment in the linear response regime, combined with the zero quantum coherence generated by the photoreaction in a weakly coupled spin pair, will reveal intensity oscillations with a beat frequency ω determined by the spin coupling and the g-factor difference of the coupled radical spins. Conditions are specified for the experimental observation of the predicted coherence phenomena.

The double (or dynamic) spin polarization in π diradicals

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe double (or dynamic) spin polarization in π diradicalsPadeleimon Karafiloglou Cite this: J. Chem. Educ. 1989, 66, 10, 816Publication Date (Print):October 1, 1989Publication History Received3 August 2009Published online1 October 1989Published inissue 1 October 1989https://doi.org/10.1021/ed066p816RIGHTS & PERMISSIONSArticle Views654Altmetric-Citations41LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

Pressure effects on the electron spin relaxation of several radicals in solution

The pressure effect on the decay rate of chemically induced dynamic electron spin polarization (CIDEP) was investigated on several free-radical intermediates in photolysis, and the spin-lattice relaxation times for these radicals were estimated from the decay rates of CIDEP signals at various pressures. The spin-lattice relaxation rates were retarded by increasing external pressure. From the pressure dependence of the spin-lattice relaxation rates the activation volume was estimated. The activation volumes of these radicals divide into two groups; ≈30 cm 3 mol −1 for negative ions and ≈10 cm 3 mol −1 for neutral radicals.

On the observables associated with zero and intermediate applied external field muon spin rotation

For zero and intermediate applied external fields, the dynamics of the static spin polarization associated with muons which have thermalized in the allowed stopping sites of a given solid is expressed in terms of counter and crystal frame spherical harmonic tensor expansions of the second-rank dynamical motion tensor. Coefficients of these expansions, usually termed relaxation functions, are related to observable longitudinal, co-planar transverse and perpendicular transverse relaxation functions which can be measured simultaneously using the skewed field technique. Since the motion tensor is of second rank then, in general, nine observable relaxation functions exist. This stands in contrast to the traditional high-field longitudinal and transverse techniques employed in muon spin rotation (ΜSR) experiments wherein only three of the nine observable relaxation functions are non-zero. These traditional experiments, usually employing different apparatus, are carried out separately. Even when the other six relaxation functions are identically zero in zero and intermediate applied field experiments, they still contain information about the stopping probabilities or the dynamical symmetries associated with the muon sites, that is, that such symmetries are not present or that the sites with these symmetries are orientated in such a way that the statistical sums of their relaxation functions are zero. Thus these relaxation functions can then be used asexperimental confirmation of expected stopping probabilities associated with one type of site for which there are different orientations or for aligned sites with appropriate dynamical symmetries.