Triplet state table

In the presence of DNA in phosphate buffer solution (cdna = 2.5 x 10 mol 1 ), the dyes with alkyl meso-substituents (K3 and K4) exhibit relatively low and close kq values for long-lived components of the decay kinetics of their triplet states (Table 1). 

In general, the anisotropic dipole-dipole interaction between the two unpaired spins in the triplet state (Table 3) gives rise to a very broad EPR spectrum, with in the derivative representation characteristic peaks for directions of B parallel to the principal axes of the dipole-dipole interaction tensor D. For reaction centers the spectrum shows a peculiar distribution of lines that are in emission or in ab-... 

Larger 1 values than V9k f have been reported for several molecules with n,T7 lowest triplet states (Table 5). Since these generally do not exceed combinations of quenching via the singlet and triplet encounter pairs have been proposed (52,82-88). In view of the high A r, So values involved, even the value of benzophenone, which is nearly equal to (compare with value for anthracene in Tables 3 and 5), can be regarded as anomalously high if only the... 

The preceding orbital phase predictions of some topological units (like 1, 4-6) can be easily extended to more complex cychc diradicals [29], as shown in Fig. 12. On the basis of TMM sub-structure (1), diradicals 8-11 are predicted to be phase continuous in their triplet states. Such a triplet preference in their ground states is in agreement with calculation results and available experiments, as listed in Table... 

T gap (cf. references collected in Table 1). This correlates well with a disfavored cyclic six-orbital interaction by the phase discontinuity in the triplet state of 7 [29] (shown in Fig. 11). In addition, TME is an important topological unit which appears frequently in many non-Kekule diradicals (as exemplified by 15-17 in Fig. 13). 

Table 2 Energy differences between the lowest singlet and triplet states of the trimethylene-based 1,3-diradicals calculated by (6,6)CASSCF and (6,6) CAS-MP2 methods with the 6-3IG basis sets...

Table 5.6 Properties of three typical photoredox-active molecules. bpy denotes 2,2 bipyridine, TMPP is tetra N-methylpyridine porphyrin Amax is the wavelength of the absorption maximum, e is the extinction coefficient at Amax, cpT is the quantum yield of the formation of the excited triplet state, r0 is its lifetime, and E0 are standard redox potentials...

To obtain more information on this point, let us examine the data given in Table 3.6<42-47> for some substituted benzophenones. The data in Table 3.6 indicate that benzophenone derivatives having lowest triplet states of n->TT character undergo very efficient photoreduction in isopropyl alcohol. Those derivatives having a lowest it- -it triplet, on the other hand, are only poorly photoreduced, while those having lowest triplets of the charge-transfer type are the least reactive toward photoreduction. In additon, in some cases photoreduction is more efficient in the nonpolar solvent cyclohexane than in isopropanol. This arises from the solvent effect on the transition energies for -> , ir- , and CT transitions discussed in Chapter 1 (see also Table 3.7). 

The photodecarbonylation of a series of dibenzyl ketones was studied by Robbins and Eastman/63 The results of this study are presented in Table 4.5. The data in Table 4.5 indicate that the presence of a p-methyl or a p-methoxy group has little effect on the quantum yield for this reaction. p-Cyano groups, on the other hand, essentially totally eliminated the decarbonylation. Since the reaction could also be quenched (inefficiently) by benzonitrile or biphenyl, it was concluded that the decarbonylation occurs from a short-lived triplet state. The effect of the p-cyano groups then could result from internal triplet quenching. 

Table 6.1. The Spin-Orbit Functions of Different Triplet States That Are Below the Lowest Singlet State [1B3u(n, tt )] of Pyrazineam...

Triplet state (cont d) intersystem crossing quantum yields, table of, 239-240 lifetime, 12 lowest triplet energies of carbonyls, table of, 224-225 of hydrocarbons, table of, 226 of various organic molecules, table of, 227... 

The bond orders for both n- n and ir - n singlet and triplet states (PPP Cl calculation) indicate (Table 7.1) that the one excited state which is not ft/ bonding is the triplet state. Such bonding is predicted to be... 

In addition, it was observed that the sensitized photolysis produced the same distribution of products with the same efficiency (fingerprint characteristic of the triplet state). From quenching studies the specific rate constant for the rearrangement could be obtained. Phenyl migration rearrangement is of intermediate efficiency, interposed between the more efficient and less efficient type A processes (Table 7.4). The type of mechanism proposed for this transformation is as follows ... 

As mentioned briefly in Chapter 5, the photodimerization of acenaphthylene is subject to a very interesting heavy-atom solvent effect. The results of the photolysis of acenaphthylene in some heavy-atom solvents are given in Table 10.6.<4a) The data in Table 10.6 show that the heavy-atom solvents n-propyl bromide and ethyl iodide yield product ratios similar to that obtained in the sensitized photolysis, indicating a greater role of the triplet state in... 

Comparison of these experimental results with the calculated charge densities (S0 and Si) at the 2 and 3 positions (Table 11.5) shows that this is the expected result. Except for those compounds discussed below, the failure to observe quenching with triplet quenchers and reaction in the presence of a photosensitizer indicated singlet reactions. Compound (89) was found to also undergo benzophenone-photosensitized substitution, indicating that the triplet state of this compound is also reactive. The reaction, however, was less clean than that observed in the direct photolysis. Similarly, 1,6-dinitro-naphthalene was found to undergo both direct and benzophenone-photosensitized substitution ... 

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. 

ESR Spectra of Biradicals, Triplet States, and other S> 1/2 Systems Table 6.1 ESR data for some organic triplet-state molecules... 

Note For the triplet states the functions are given only for the Ms = 1 spin component. For all degenerate levels the a components (as given by the vector coupling coefficients of Table 2) are listed first, and these transform as +1 under oxz and the b components as - 1 under the same operation. 

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