Quantum yield data

Quantum yield data for several processes that occur on photolysis of 5-4-methyl-1-phenyl-l-hexanone have been determined. The results are tabulated below for benzene as solvent. 

Tabu 6.6. Isomerization Quantum Yield Data for Compounds (7), n = 1-4... 

A short summary of quantum yield data is given in Table 9.1. Equations (9.11) and (9.12) can be easily derived from the suggested mechanism ... 

Region B 1600-2100 A. Quantum yield data for the photolysis of pure N20 in this wavelength region are summarized in Table 10. The widely accepted [Pg.70]

Region C 1380-1600 A. The absorption spectrum is highly structured in this region138, so that significant participation of electronically excited N20 is a distinct possibility. Quantum yield data (Table 10), however, suggest that the... 

Fig. 6 Typical PET probes (a) and representative fluorescence light-up responses toward selected metal ions in tabulated (b) and graphical form (c trace 1 = 14, trace 2 = 14-(Zn2+)2, trace DMA = 9,10-dimethylanthracene in MeCN). Color code coordinating atoms in blue, atoms which take part in the complexation and show (main, in 14) PET activity in orange, fluorophore in green. Lincoln and co-workers have demonstrated that the attachment of two dimethylamino groups through propylene spacers to the 9,10-positions of anthracene has a more than 100-fold weaker PET activity than the attachment through methylene spacers [62]. The blue N atoms in 14 are thus predominantly responsible for coordination. For symbols, see Fig. 3. Quantum yield of 14 in MeCN estimated from intensity readings published in [61] and quantum yield data of the parent compound without active PET, DMA, published in [63]. (Reprinted in part with permission from [61]. Copyright 1988 American Chemical Society)...

The rate of disappearance of the diazo compound, e.g. the quantum yield of the photolysis, should be independent of the nature and concentration of the reactants. This is the kinetic criterion for the intermediacy of a free carbene. The quantum yield data of diazo compound photolyses are shown in Table 1. Carbenes are named in the usual way by using... 

Fig. 12. Quantum yield data for CH4 and H2 production from the borazine-CHsBr reaction. In des nated runs added gases were CO2 and Xe. Points with vertical arrows represent true 184.9 nm yields, corrected for the CH3Br absorption at 253.7 nm...

Quantum yield data for photochemically initiated ligand exchange reactions of a number of chromium(III) complexes having ligand fields of effective Oh symmetry are given in Table III. These data show that... 

Experimentally, while the determination of absorption cross sections is fairly straightforward, measuring primary quantum yields is not, due to interference from rapid secondary reactions. As a result, in cases where quantum yield data are not available, calculations of maximum rates of photolysis are often carried out in which it is assumed that (A) = 1.0. It should be emphasized in such cases that this represents only a maximum rate constant for photolysis the true rate constant may be much smaller, even zero, if photophysical fates of the excited molecule such as fluorescence or quenching predominate. 

For the following problems, where necessary use absorption cross sections and quantum yield data found in the relevant sections of Chapter 4. 

Figure 4. Determination of G(s) and G(x) for PTBIPK. Table II. Summary of Quantum Yield Data...

From the quantum yield data of Table I we can estimate the ratio of kg/(k7 + kH). For these experiments at relatively low light intensities the butyl radical consumption by oxygen is complete, and it is highly likely that Reactions 7 and 8 are the major paths by which it reacts for these conditions. 

The effects of substituents and solvent polarity on the luminescence properties also have been evaluated for of a series of bichromophoric anthronyl-substituted anthracenes 98 and 99. It can be concluded from the quantum yield data summarized in Table 20 for spiro-substituted compounds 98a e that, dependent on solvent polarity, two different modes of intramolecular interactions between the electronically excited anthracene chromophore and the ground state ketone typically are operative, and both types of interaction result in fluorescence quenching. In nonpolar solvents, fluorescence quenching apparently involves endothermic intramolecular... 

Photoexcitation of lepidopterene 118 (L Y = H in cyclohexane solution results in cycloreversion and gives the electronically excited product E whose deactivation to ground state is characterized by the structureless emission around 600 nm (see Figure 32). The quantum yield of the E emission is 0.58 (0.80), while that of the emission from the locally excited state L is only 0.005 (0.016). (The lower quantum yield data have been reported by... 

Table IV summarizes the quantum yield data for interconversion of XIA and XIB by visible and ultraviolet radiation...

TABLE 9. Kinetic and Quantum Yield Data for the Reactions of Singlet and Triplet Diphenylvinylene Carbonate with Vinyl Ethers9... 

Stern-Volmer constant from product quantum yield data and limiting quantum yield for triplet sensitized reactions. 

Both the fluorescence and intersystem crossing of lt -amine exciplexes can be quenched by added amine (116). Rate constants for exciplex quenching obtained from fluorescence or t-1 isomerization quantum yield data decrease with amine a-alkylation ... 

TABLE 12. Quantum Yield Data for Reactions of trans-Sti1bpne with Tertiary Amines3... 

Rate constants for quenching of 1-7 by methanol and acetic acid in hexane solution from fluorescence quenching and quantum yield data are 10 M l-s-l-. Limiting quantum yields for adduct formation are 0.1. The observation of reactions of protic solvent with 1-7 but not 1-t may reflect the longer lifetime and/or enhanced reactivity of the cyclic molecule. While photo-induced nucleophilic addition is a common reaction of aryl olefins, it is normally observed to occur only under conditions of electron-transfer sensitization (139). Under these conditions, it is the aryl olefin cation radical which undergoes nucleophilic attack. The reaction of 1-7 with protic solvents appears to be the only reported example of nucleophilic trapping of an aryl olefin it,it singlet state (140). 

Constants or lifetimes of the excited states are important parameters since the reactivities of these energy states depend on them. Rate constants of various photophysical and photochemical processes can be adduced from quantum yield data only if the mean radiative lifetimes (t0) are known. The defining relationships are (Section 5.3)... 

The quantum yield data for polymer 5 in Figure 3 has an exponential dependence on the inverse temperature, and activation parameters were... 

Podoll et al. (1986) used the quantum yield data of Dulin et al. (1986) for a water acetonitrile solution to calculate seasonal half-life values for dissolved 2,3,7,8-TCDD at 40 degrees north latitude in clear nearsurface waters. Photolysis half-lives for dissolved 2,3,7,8-TCDD in sunlight range from 118 hours in winter, to 51 hours in fall, to 27 hours in spring, to 21 hours in summer (Podoll et al. 1986). Choudhry and Webster (1989) studied photolysis of a series of CDDs in a water acetonitrile solution (2 1 v/v). 

The Rh(III)- and lr(lll)-ammines undergo efficient photosubstitution in marked contrast to the Co(III) analogues as mentioned above. However, the efficient photosubstitution found for the second and third row metal systems does appear to obey the essential rationalizations outlined in the models for LF substitutional reactivity. Two sets of complexes seem to behave quite nicely in this regard C4v, Rh(NH3)s X2+ 58) and DAh trans-M(en)2Xl (M = Ir, Rh X = Cl, Br, I).59,6°) In both sets of complexes the lowest excited state is likely one which features population of the d22(a ) orbital. Consistent with this fact, the photosubstitution chemistry can be viewed as resulting from loss of a ligand on the z-axis. For the Rh(III)-amines a dissociative mechanism is suggested for Cl photoaquation by the quantum yield data in Table 8.60) The... 

Cl, Br, I).68b) Some quantum yield data for these reactions are shown in Table 12 and some electronic spectra are given in Fig. 2. Despite the remarkable similarity in the... 

Styrylpyridine photochemistry has been important in one other system. The photoprocesses in the complexes W(CO)sX (X = pyridine, 2-styrylpyridine, and 4-styrylpyridine) have been investigated.129 Unlike the XRe(CO)3(taz s-styryl-pyridine)2 and Ru(II)-styrylpyridine complexes having lowest IL and CT states, respectively, the W(CO)5X complexes have lowest LF excited states with only a small contribution from W - pyridyl CT. The one-electron diagram for low-spin d6, Cnv complexes shown in Scheme 7 is appropriate here. Both photosubstitution and photoisomerization reactions are found for the W(CO)5X complexes and some quantum yield data are found in Table 23.129 The data show that substitution efficiencies for... 

Table 5 Emission, lifetime, and quantum yield data of complexes 46, 51, and 52 measured at 298 K in dichloromethane...

Table 9 Reaction Mechanism for the 03/H202/UV System Elementary Reactions, Reaction Rate Constant, and Quantum Yield Data ... 

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