Zero-Field Optically Detected Magnetic Resonance ODMR

Zero-Field Optically Detected Magnetic Resonance (ODMR) 

This work verifies El-Sayed s earlier suggestion that and Sn,x T . are at least one order of magnitude more probable than 

Work on intermolecular energy transfer at low temperature from a donor (D) to an acceptor (A) has indicated that if a donor is prepared such that its triplet state has a unique spin direction, the acceptor will also have a unique and predictable direction when both donor and acceptor are oriented in a single crystal.  

Phosphorescence microwave multiple resonance studies are likely to grow in importance in the next ten years as more systems are studied. 

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Optically detected magnetic resonance (ODMR) has yielded valuable information about dynamics of long-lived pholoexcitations of conjugated polymers. The technique relies upon the paramagnetic interaction of excitations with an applied magnetic field. For a particle with non-zero spin, placed in a magnetic field, the Hamiltonian is ... 

Fig. 9. ODMR investigations at T = 1.4 K of Pd(2-thpy)2 dissolved in an n-octane Shpol skii matrix. Concentration = 10 mol/1 cw excitation Ag c = 330 nm (30.3 x 10 cm 0- Detection of the emission at 18418 cm (Tj —> Sq transition), (a) Zero-field ODMR (optically detected magnetic resonance) spectrum (b) Zero-field microwave recovery ODMR signal after pulsed microwave excitation with a microwave frequency of 2886 MHz. The best fit of the recovery signal is obtained with Eq. (4). (Compare Ref. [61])...

Optical detection of magnetic resonance (ODMR) was attempted for measurements of the pH effects on the triplet state of purine to investigate the protonation site of purine at low temperatures (78JA7131). The ODMR spectrum did not show the presence of more than one triplet state at liquid helium temperatures. Since the protonated tautomers 1H,9H (3a) and H,1H (3b) have similar bond structures, their triplets should have similar zero-field parameters and are thus not easy to distinguish by ODMR. 

This mechanism leads to a highly spin-polarized triplet state with a characteristic intensity pattern in the EPR spectrum, which is observed by time-resolved techniques (either transient or pulse EPR). The zero field splitting (ZFS) of the triplet state, which dominates the EPR spectrum, is an important additional spectroscopic probe. It can also be determined by optical detection of magnetic resonance (ODMR), for a review of the techniques involved and applications see reference 15. These methods also yield information about dynamical aspects related to the formation, selective population and decay of the triplet states. The application of EPR and related techniques to triplet states in photosynthesis have been reviewed by several authors in the past15 22-100 102. The field was also thoroughly reviewed by Mobius103 and Weber45 in this series. 

UV spectra were obtained with a Varian spectrometer (Cary 15 and 17). Fluorescence, phosphorescence spectra, and the zero-field splitting parameters D and E of the triplet state were determined at 1.3K with an apparatus (31) for optical detection of magnetic resonance (ODMR) which was similar to the one described by Zuclich et al. (32). 

If the separation among the sublevels is in the range of microwave frequency, sublevel properties can be obtained by observing the effect of microwave resonance on the emission from this state. The zero-field splitting is of the order of microwave frequency for most of rr/r states. Thus, the sublevel properties can be obtained by analyzing the effect of microwave resonance on the phosphorescence intensity. The method is called phosphorescence-microwave double resonance (PMDR) or optical detection of magnetic resonance (ODMR). 

Knowledge of the magnetic (and optical) properties of triplet states has been greatly enhanced by the development of zero-field (zf) resonance techniques, especially those employing optical detection. In what follows, we review the selection rules which govern the transitions in the zf experiment. We then present recent results from this laboratory on the lowest (nTc ) states of 1-halonaphthalenes and discuss in some detail the analysis of these spectra and their significance with respect to the intramolecular heavy-atom effect on the properties of the parent molecule. Next, we survey some representative results from other laboratories, including zf EPR, ODMR, ENDOR, and ELDOR experiments, and close with a brief description of other zf applications. 

Spin selective information on the lowest triplet state decay was obtained by optical detection of magnetic resonance transitions between the spin components of the T state of FBP in n-octane. Because of the absence of phosphorescence at these conditions, the ODMR signals were detected via changes in the 5i->5o fluorescent intensity [6, 29], Our calculations reproduce the fluorescent frequency and radiative constant rather well. In order to complete the interpretation of the microwave-induced fluorescent ODMR measurements [6, 29] one has to calculate the zero-field splitting in the T state and hyperflne coupling between electron and nuclear spins. 

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