Wavelength dependent photoreaction

Lambrych KL, JP Hassett (2006) Wavelength-dependent photoreactivity of mirex in Lake Ontario. Environ Sci Technol 40 858-863. 

A wavelength-dependent photoreaction has been described in thecarbonyl-containing thiiran (131)113 irradiation at X = 254 nm gave the alkene (132), whereas irradiation at X > 280 nm gave products 133 and 134 arising by Type I cleavage, followed either by elimination of carbon monoxide or by cyclization to the oxacarbene. 

The eight-coordinate (fi complexes [Mo(CN)g]" and [W(CN)g] undergo two wavelength-dependent photoreactions. Photolysis in the short-wavelength (254 nm) region leads to efficient photoelectron production from an excited state assigned as CTTS in character. Irradiation... 

Murata, S., Kobayashi, I., Kongou, C., Miyata, M., Matsushita, T., and Tomioka, H., Remarkable wavelength-dependent photoreactions of the bis(diazo)ketone having inequivalent diazo groups studies in fluid solutions and in low-temperature matrixes, /. Org. Chem., 65, 6082, 2000. 

Wavelength-Dependent Composition of the Equilibrium Photoreaction Mixture of 2-Diphenyl-l,3-indanedione (44 Rj. = R2 = C6H5) in Benzene1811... 

Metal perturbation of IL photochemistry appears to be less important in [Ru(bipy)2(h- n.s-4-stilbazole)2]2+ and [Ru(bipy)2(cw-4-stilbazole)2]2+. Both complexes undergo wavelength-dependent isomerization of the coordinated stilbazole ligands as the only important photoreaction."4 This wavelength dependence has beep attributed to the presence of two different types of reactive excited states, aRu-t stilbazole CT state which favors formation of the trans isomer and a higher energy IL state localized on stilbazole which decays with nearly equal probability to the two isomers. The latter pathway is qualitatively similar to the isomerization process that obtains upon direct photolysis of the free ligand. Thus coordination to Ru has not altered the characteristic photoreaction mode of the stilbazole molecule. 

The work reports wavelength dependent quantum yields for the photoreaction and photosubstitution yields for the Os(III) complex are much lower than those of the iron or ruthenium analogs. The authors also report that the complexes exhibit weak luminescence in the green the Os(III) complex has a reported emission yield of 0.008 [35]. 

Evidence has been provided that adsorption of several (t] -arene)tricarbonylchromium(O) complexes on to silica gel can perturb the electronic structure of these complexes and the quantum efficiencies with which they undergo photodecomposition. The steric constraint imposed by the support also seems to influence the photoreactivity of these complexes. M(CO)4(bipym) (where M = Cr or W, bipym = 2,2 -bipyrimidyl) and (W(CO)4]2(bipym) both have a lowest MLCT state, and on irradiation CO is lost. Wavelength-dependent quantum yields have been obtained for this transformation and at 366 nm = 2.4x 10 quanta/min for Cr-bipym, 2.5 x 10 quanta/min for W-bipym, and 1.1 x 10 quanta/min for W-bipym-W." Correlations have been described between the MLCT absorption energies of a series of M(CO)4 diimine complexes and Reichardt s solvent parameters (Et), and Kamlet s and Taft s solvent polarity scale Paramagnetic complexes... 

Intramolecnlar.—The photochemical reactivity of dienone (1) has been shown to be associated with the Si or the T2 state, since the photoreactions undergone cannot be quenched or sensitized. The reactions are wavelength dependent such that at 313 nm initial Norrish Type I fission is followed by radical recombination (as was established by deuterium labelling studies) to give the... 

In contrast to the typical behavior of organic compounds discussed above, many photoreactions of transition metal complexes have wavelength-dependent quantum yields (7). Generally, these wavelength effects have been interpreted in terms of more than one reactive excited state of the photolyzed species. The photoreactivity of V(CO) L (L = amine), for example, has been interpreted in this manner with the previously mentioned model of substitutional photoreactivity proposed by Wrighton et al. (42, 49,73). Assuming ligand dissociation to be the only primary photochemical process (Section III-B-1), photolysis of W(C0)5L could produce three primary products ... 

The quantum yield is the fraction of absorbed radiation that results in photoreaction. According to the Kasha-Vavilov law, the quantum yield for a photoreaction in solution in which only a single substance is the chromophore (e.g., direct photoreactions) is generally wavelength-independent, although there are some exceptions. With indirect photoreactions in natural waters, a mixture of chromophores is involved. Thus, the apparent quantum yield for an indirect photoreaction in a natural water sample usually is significantly wavelength-dependent. 

Various approaches have been used to model the rates of photoreactions in aquatic environments [3-6,8-10,67,68,139-141]. To illustrate the utility of the modeling approach, the wavelength dependence for CO photoproduction fluxes simulated for a mid-latitude location is shown in Figure 5. Quantum yield spectra that are shown in Figure 4 were used in these calculations. The equations and assumptions involved in these calculations are discussed in more detail in... 

The photochemistry of vitamin D (see also Special Topic 6.4 above and Scheme 6.8) has also played a central role in the development of modern organic photochem-istry.564,598,617 618 The concept of non-equilibration of excited rotamers (NEER Section 6.1.1) has been used to explain the excitation-wavelength dependence of E Z isomerization (Section 6.1.1) of previtamin D3 (41).619 Whereas the quantum yield for E Z isomerization decreases with increasing wavelength, the formation efficiencies of the 6jt-electron conrotatory ring-closure products, diastereomeric 7-dehydrocholester-ol (provitamin D) (64) and lumisterol (65) (Scheme 6.22), increase dramatically. This was found to occur on the basis of a participation of both the Si and S2 excited states in the photoreaction.620 For example, the quantum yields of 64 and 65 formation were [Pg.244]

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