Triplet states detection

Mg(Etio I), IL, 3IL Nitroaromatics Benzene Formation of both singlet and triplet exciplexes (A — Q) suggested three-component exciplexes (Q — A — Q) in triplet state detected [35-37]... 

The method of triplet state detection in dye labelled proteins by fluorescence recovery spectroscopy has been described in a paper presenting this new method . ... 

Fig. 15a,b. a Optically detected microwave recovery transients for the three zero-field ODMR transitions of [Rh(thpy)2(bpy)j in the excited triplet state. Detection is at 520.7 nm. b Optically detected adiabatic rapid passage transients for the three zero-field ODMR transitions of [Rh(thpy)(phpy)(bpy)]+ in the excited triplet state. Detection is at 519.9 nm, T= 1.4 K... 

Corin, A. K Blatt, E. Jovin, T. M. Triplet-state detection of labeled proteins using fluorescence recovery spectroscopy. Biochemistry 1987, 26, 2207-2217. 

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. 

The comparatively small size of the simplest carbene (methylene) ensures that it has a definite mobility in frozen inert matrices, which leads to the formation of dimerization products under these conditions. It became possible only in 1981 to detect in the spectra of the diazomethane photolysis products bands at 1115 cm (Ar matrix) and 1109 cm (Xe matrix) which were attributed to the deformation vibration of methylene in its ground triplet state (Lee and Pimentel, 1981). 

Fujii, R. et al., Cis-to-trans isomerization of spheroidene in the triplet state as detected by time-resolved absorption spectroscopy, J. Phys. Chem. A, 106, 2410, 2002. Montenegro, M.A. et al., Model studies on the photosensitized isomerization of bixin, J. Agric. Food Chem., 52, 367, 2004. 

The measurement of Tg is straightforward when Trp<triplet lifetime can be shortened by addition of triplet quenchers, and the values of Tg for PPVK and CoPT(l) have been obtained using this approach (6). Figure 2 shows a typical trace corresponding to the decay of the biradical from PTVK, as monitored at l 15nm. The triplet state is in this case too short lived to be detectable the residual absorbance observed after decay of the biradical is due to the enol. 

The fluorescent components are denoted by I (intensity) followed by a capitalized subscript (D, A or s, for respectively Donors, Acceptors, or Donor/ Acceptor FRET pairs) to indicate the particular population of molecules responsible for emission of/and a lower-case superscript (d or, s) that indicates the detection channel (or filter cube). For example, / denotes the intensity of the donors as detected in the donor channel and reads as Intensity of donors in the donor channel, etc. Similarly, properties of molecules (number of molecules, N quantum yield, Q) are specified with capitalized subscript and properties of channels (laser intensity, gain, g) are specified with lowercase superscript. Factors that depend on both molecular species and on detection channel (excitation efficiency, s fraction of the emission spectrum detected in a channel, F) are indexed with both. Note that for all factorized symbols it is assumed that we work in the linear (excitation-fluorescence) regime with negligible donor or acceptor saturation or triplet states. In case such conditions are not met, the FRET estimation will not be correct. See Chap. 12 (FRET calculator) for more details. 

The detection of zero-field splitting for dianions of [18] or [21] is very important it reveals not only the existence of a triplet state, but it also provides information on the mode of spin density distribution. Even more... 

Any unsaturated molecule has diradical as well as singlet (nonradical) states. Usually one of the non-radical states will have a decisively lower free energy than the most stable of the diradical states, in which case the substance is not paramagnetic. Special circumstances can make the diradical state the ground state then the singlet state is an excited one. Some substances have detectable amounts of both forms in equilibrium. It is unknown whether the radical-like reactions of some compounds are characteristic of their singlet states directly or due to an undetectable amount of a more reactive triplet state in equilibrium. 

Both l3A"-4b and 23A"-4b are predicted to be minima on the potential surface at the CASSCF level.61 This is in contrast with the situation for 4a, where one triplet state is calculated to be a transition state for pseudorotation of the other.55-57 A derivative of triplet 4b has been implicated in solution trapping experiments,49 but there have been no reports of the direct observation of 4b. Facile intersystem crossing from the triplet ground state (13A") to the open-shell singlet state ( A"), followed by vibrational relaxation to one of the enantiomers of 3b (Fig. 12), would be expected to rapidly depopulate the 13A" state of 4b. Thus, direct detection of triplet 4b may prove to be much more difficult than detection of 4a was.lla... 

Menadione (79) has been shown by Krishna et al. to act as a photosensitizer for thymine degradation. Spin-trapping experiments with several nucleosides showed that the photosensitizations occurred by electron transfer from the substrate to the excited triplet state of menadione to form the cation radical of the substrate and the anion radical of menadione, both of which were detected... 

This photoreaction has been investigated by laser flash photolysis58 and quantum yield measurements that identify the triplet state (r = 6 nanoseconds) as the reactive species, and show intermediate 82 is sensitive to hydroxylic molecules, but the logical precursor biradical intermediate 81 could not be detected owing to a short lifetime (equation 48). 

A new triplet diradical is detected by ESR from the photolysis of 2-nitrobiphenyl106 (equation 85). The spectrum shows a temperature dependence which implies that the observed triplet state is a ground state. 

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