ODMR

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. 

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 ... 

The ODMR spectrometer resembles the PA spectrometer shown in Figure 7-1, with the sample placed in a microwave cavity between the pole pieces of an electromagnet. The sample is constantly illuminated by the pump and probe beams amplitude-modulated microwaves arc coupled into the cavity through a waveguide. Changes Si in PL or ST in probe transmission are delected by lock-in am-... 

Figure 7-33. ODMR spectra of pristine and C o-doped DOO-PPV. Inset hall-field signal of doped sample.

Do results obtained from ODMR or OPNMR of semiconductor nanostructures such as quantum wells have relevance to the nanoscopic semiconductors synthesized and studied by chemists ... 

Optically detected magnetic resonance (ODMR) studies of -iT-conjugated polymer-based hght emitting diodes (LEDs) J. Shinar Organic Electroluminescent Materials and Devices, S. Miyata and H.S. Nalwa, Eds., Gordon and Breach, Amsterdam, pp.177-202... 

D was determined by measuring the Ams = 2 EPR transition, where ms is the spin quantum number. Several years later, D and E were obtained directly by observation of the Ams = 1 EPR signals/33 1 In 1973, Zuclich et alP redetermined the triplet-state splitting parameters of tyrosine using optically detected magnetic resonance (ODMR) spectroscopy. 

The most direct demonstration of triplet-triplet energy transfer between the aromatic amino acids is the ODMR study by Rousslang and Kwiram on the tryptophanyl-tyrosinate dipeptide.(57) Since the first excited singlet state of tyrosinate is at lower energy than that of tryptophan, it is possible to excite tyrosinate preferentially. The phosphorescence of this dipeptide, however, is characteristic of tryptophan, which is consistent with the observation that the triplet state of tyrosinate is at higher energy than that of tryptophan, making tryptophan the expected triplet acceptor. 

Phosphorescence and ODMR are additional spectroscopies that can be used to investigate intramolecular interactions that affect tyrosine residues in proteins and polypeptides/215,216) An example is tyrosine and tyrosinate in horse liver alcohol dehydrogenase.(202) The same approach has been used to study the role of tyrosine in the mechanism of action of carboxypeptidase B.(21/,218) jn botli these proteins, as in other proteins which contain both... 

In 1979, Ross et al 22i" measured the ODMR of tyrosine in glucagon and the derivative [12-homoarginine]glucagon to examine the effect of chemical modification of a lysine residue adjacent to Tyr-10 and Tyr-13. The guanidinated analogue had lower potency than glucagon in a fat cell hormone receptor assay. Since the tyrosine ODMR and other spectral properties of the polypeptide, including circular dichroism, were essentially identical, it was... 

The kinetic decay rate constant of the y-triplet level determined by ESE measurements and reported in Table I can be converted to the equivalent lifetime. This lifetime equals 1 05 ms for TPP in a 1 1 mixture of toluene and ethanol as the solvent. This is consistent with ODMR measurements (13) of the same level for TPP in n-octane where the lifetime equaled 1.45 ms. 

As in the case of hexafluorobenzene solvent anion, EPR and ODMR spectroscopies suggests that no dimerization of monomer radical anions of benzene and toluene occur in liquid benzene and/or in alkane solutions of benzene (whereas the radical cation of benzene is known to dimerize rapidly). The conductivity studies also indicate that there is no volume change associated with the dimerization [45]. 

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. 

The main result of the early EPR and ODMR work was a reduction of the ZFS parameters D( and when comparing monomeric 3BChl and the 3P state of the primary donor in bRCs (for a collection of data see reference 22). This has been interpreted as resulting from a delocalization of the triplet exciton in the BChl-dimer. However, due to the complexity of the electronic system, that could also involve charge transfer states, a final quantitative conclusion has been difficult. From a determination of the triplet axes in bRC single crystals104 107 it was concluded that in R. sphaeroides the triplet is indeed delocalized whereas in B. viridis it seems to be located on one monomeric BChl b half. 

The zero field splittings of similar Rh3 + and Ir3 + complexes fit well into this picture. For the 3LC emitter [Rh(bpy)3] (C104)3 ODMR measurements gave a ZFS of 0.12 cm 1 [71] and for [Ir(5,6-(CH3)2-phen)2Cl2] which also shows a 3LC type luminescence a ZFS of 3 cm 1 was derived from Zeeman experiments [72],... 

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