Optical nuclear polarization via hyperfine relaxation. Polarization mechanism in anthracene/tetracyanobenzene charge-transfer crystals

Allgeier, J.; Macho, V.; Stehlik, D.; Vieth, Hans‐Martin; Auch, W.; Schütz, J.U. von

doi:10.1016/0009-2614(82)80185-1

Cited by 17 publications

(4 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…A numeric calculation of the excitonic ONP field dependence using the simple model described in Ref. 6 reproduced well the characteristic features for B II x*, y*, z*, but not the Fig. 3 (inset).…”

Section: Energy Levels and Excitation Schemementioning

confidence: 71%

See 1 more Smart Citation

Optical Nuclear Spin Polarization (ONP) Studies of Short‐Lived Excited Triplet States in Anthracene Crystals Doped with Phenazine. Structure and Mechanism of Reversible Photochemical H‐Transfer

Buntkowsky

Nack

Stehlik

et al. 1989

Israel Journal of Chemistry

Self Cite

View full text Add to dashboard Cite

Abstract. In anthracene crystals doped with phenazine two types of ONP active triplet states are identified: delocalized triplet excitons of anthracene and localized triplet states with small zero-field splitting and characteristic hyperfme interaction (hfi). All three basic ONP mechanisms can be demonstrated in one system with transfer of the photoinduced electron polarization (OEP) to the nuclear spins by (a) static hfi in the level crossing region (LAC-ONP), (b) time modulated hfi inducing electron-nuclear cross relaxation (Overhauser effect) and (c) rf saturation of forbidden transitions (RF-ONP, solid effect). The localized triplet states are identified as a radical pair product of a H-transfer photoreaction, in which an H atom is abstracted from an anthracene X-trap to the neighboring phenazine guest molecule, between two translationally equivalent lattice sites along the crystalline b-axis. Kinetic rates determined with RF-ONP techniques indicate a cyclic reaction with slow radical pair product formation and faster, spin selective, triplet product decay. Analogies are discussed with similar H-transfer reactions in doped fluorene. Whereas anthracene acts as H-acceptor when doped in fluorene, it becomes H-donor in the anthracene crystal doped with phenazine.

show abstract

Section: Energy Levels and Excitation Schemementioning

confidence: 71%

“…The most detailed analysis was done on the 1:1 charge transfer crystal anthracene/ TCNB. 6 It was shown that a broad field …”

Section: Separation Of Onp Active Triplet Statesmentioning

confidence: 99%

Optical Nuclear Spin Polarization (ONP) Studies of Short‐Lived Excited Triplet States in Anthracene Crystals Doped with Phenazine. Structure and Mechanism of Reversible Photochemical H‐Transfer

Buntkowsky

Nack

Stehlik

et al. 1989

Israel Journal of Chemistry

Self Cite

View full text Add to dashboard Cite

show abstract

“…By means of hyperfine coupling this order of electronic spins is partially transferred to neighboring nuclear spins. Particular transfer mechanisms are (a) mixing of state, (b) cross relaxation with joint electronic and nuclear spin flips, and (c) resonant irradiation of radio frequencies. , The short-lived T 1 state decays back into S 0 , but this process does not affect the nuclear spin orientation. Thus, we obtain ground-state spin polarization.…”

Section: Optical Nuclear Polarizationmentioning

confidence: 99%

Application of Optical Nuclear Polarization Enhanced ¹³C NMR

et al. 1998

View full text Add to dashboard Cite

A gain in detection sensitivity of more than 3 orders of magnitude has been achieved in high-resolution solid-state 13C NMR of monocrystalline fluorene doped with acridine by applying optical nuclear polarization (ONP) via excited triplet states to protons and transferring this proton polarization to the 13C nuclei. This sensitivity gain was utilized to measure the angular dependence (rotation pattern) of the 13C NMR lines. In this way the principal values and orientations of all 13C chemical shielding tensors were determined. While the 13C shielding tensor of the bridging methylene group exhibits only a small anisotropy, at the aromatic carbon positions the typical strong anisotropy is observed. All tensors belonging to the same molecule have one principal axis, perpendicular to the molecular plane, in common, showing that in the crystal lattice the fluorene molecule is in a planar configuration. The experimental data are compared to ab initio calculations employing optimized geometries and gauge included atomic orbitals density functional theory (GIAO DFT). The orientations of all calculated tensors are in excellent agreement with the experimental data. On an absolute scale the calculated shielding parameters reproduce the experimental values reasonably well. A significant improvement of the calculated eigenvalues is achieved by shifting the tensors employing data from calculations of benzene and methane.

show abstract

“…Second, electron spin relaxation occurs in the excited triplet state. There are in principle three different ( 4) relaxation rates, one for each .pairing of electron spin sublevels. Third, decay from the excited triplet state to the ground singlet state may again be selective, in the sense that the three electron spin sublevels may decay at different rates • .…”

mentioning

confidence: 99%

Time-resolved optical nuclear polarization by rapid field switching

Tycko

Pines

Stehlik

1982

Chemical Physics Letters

Self Cite

View full text Add to dashboard Cite

Optical nuclear polarization via hyperfine relaxation. Polarization mechanism in anthracene/tetracyanobenzene charge-transfer crystals

Cited by 17 publications

References 18 publications

Optical Nuclear Spin Polarization (ONP) Studies of Short‐Lived Excited Triplet States in Anthracene Crystals Doped with Phenazine. Structure and Mechanism of Reversible Photochemical H‐Transfer

Optical Nuclear Spin Polarization (ONP) Studies of Short‐Lived Excited Triplet States in Anthracene Crystals Doped with Phenazine. Structure and Mechanism of Reversible Photochemical H‐Transfer

Application of Optical Nuclear Polarization Enhanced ¹³C NMR

Time-resolved optical nuclear polarization by rapid field switching

Contact Info

Product

Resources

About

Optical nuclear polarization via hyperfine relaxation. Polarization mechanism in anthracene/tetracyanobenzene charge-transfer crystals

Cited by 17 publications

References 18 publications

Optical Nuclear Spin Polarization (ONP) Studies of Short‐Lived Excited Triplet States in Anthracene Crystals Doped with Phenazine. Structure and Mechanism of Reversible Photochemical H‐Transfer

Optical Nuclear Spin Polarization (ONP) Studies of Short‐Lived Excited Triplet States in Anthracene Crystals Doped with Phenazine. Structure and Mechanism of Reversible Photochemical H‐Transfer

Application of Optical Nuclear Polarization Enhanced 13C NMR

Time-resolved optical nuclear polarization by rapid field switching

Contact Info

Product

Resources

About

Application of Optical Nuclear Polarization Enhanced ¹³C NMR