Intersystem crossing quantum yields, table

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... 

Intersystem crossing quantum yields determined by the methods discussed in this section and other methods<24) are presented in Table 5.6. 

Table 5.6. Intersystem Crossing Quantum Yields for Various Organic Molecules...

Representative values of intersystem crossing quantum yields obtained in this manner are shown in Table IV (Hammond et al., unpublished results). 

For the photodiagnostic use of these compounds, a high quantum yield of fluorescence, r, is desirable. The metal complexes of the common first-row transition metals are not suitable, because they show very low 4>f values. On the other hand, porphyrin complexes of d° and d10 elements show appreciable fluorescence, although generally less than that of the metal-free compounds, presumably because of the heavy-atom effect (e.g., TPP ZnTPP, Table 5). The further operation of the heavy-atom effect, which increases the rate of intersystem crossing (/cisc) by... 

Using the values of quantum yields and fluorescence lifetime, rate constants on the state were obtained. The results are summarized in "Table III". As seen in "Table III", no isotope effect is observed in the rate constants for the fluorescence and intersystem crossing. On the other hand, in the case of TPP the rate constants of internal conversion show a large isotope effect that of D2TPP is... 

Table 22. Excited State Parameters of the Helicenes. Quantum yield of fluorescence (

In Table 1 we have collected data on measured lifetimes and quantum yields in various solvents for [Ru(bpy)3]2+. Also included is a calculated quantum yield from the observed lifetime, assuming a constant value for the radiative lifetime (14 ps174,192)). Demas and Crosby188 have argued that the intersystem crossing efficiency to populate the emitting MLCT triplet is unity and should be independent of solvent Bolletta et al.193)... 

Table 9 Quantum Yield of 02 Generation (ISc) by Isomeric Bis-Adducts (34,35,36)...

Table I shows that in either dioxane or acetonitrile the quantum yield for degradation of I, is unaffected by the presence of 0.1 M of triplet quencher, either sorbic acid, naphthalene or cyclohexadiene. In ethanol, triplet quenchers reduce < >d from 0.34 to 0.14. Quantum yields for intersystem crossing, as determined by a laser opto-acoustic technique ( ), were 0.36 in ethanol and 0.59 in dioxane. These results agree with our earlier report (3), and indicate that significant reactivity occurs from St of I in protic solvents, and that reaction occurs exclusively from Sx in aprotic solvents. While triplet quenching experiments cannot rigorously exclude participation by short-lived higher triplet states, Palm et al (9) have obtained conclusive evidence from CIDNP experiments for singlet-state participation in a series of aryloxy-acetophenones. Note that the triplet state of I is formed in aprotic solvents, and that in deaerated solutions at room temperature it decays by first-order kinetics with a lifetime of 200 ns (3). Remarkably, despite having lifetimes about 100 times longer than other, differently-substituted, aryloxyacetophenones (the longer lifetimes may...

Thiopyrylium salts not only absorb in the visible region but also exhibit considerable fluorescence emission such that they have value as photosensitizers. The fluorescence properties of several thiopyrylium salts have been studied and are collated in Table 12. Although the fluorescence (Amax) is red-shifted by 30-60 nm compared with the corresponding pyrylium salts, the quantum yields ((pf) are appreciably lower, attributed to the higher efficiency of the forbidden singlet-triplet transition because intersystem crossing is efficient <1995BCJ2791>. 

The bridged cyclohexenediones whose photoisomerization to cyclobutanediones have been observed are summarized in Table II where it can be seen that a wide variety of compounds undergo this reaction. In all cases where the point has been checked, quantum yields for disappearance of starting material and for formation of product were identical. The series of compounds, entries 13-17, were of interest since they involve unsubstituted (entry 13), tetrachloro (14, 16) and tetrabromo (15, 17) isomers where heavy atom effects on intersystem crossing rates might be manifested in quantum yield variations. As can be seen in the Table, the results do not permit such an interpretation. 

Since the quantum yield for disappearance of ketone (triplet ketone nor the primary radical pair PhCH2CO CH2Ph is scavenged. As stated above, the proposed mechanism for the photolysis of DBK in micellar solution is illustrated in Fig. 5 13,21). The micellar environment inhibits the diffusion of radicals to the bulk aqueous phase the radical pair s distance maximum separation is maintained to a few tens of angstroms or less. The amount of escape being reduced, the radicals can then undergo more efficient intersystem crossing and recombination. 

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