Spectral photochemical

Table 8.7. Spectral, Photochemical, and Kinetic Parameters of the Photochromic Reactions of bis-Spirocyclic Compounds 21 and 22 (toluene, 24°C) and their Protonated Forms (Formed by an Addition of 3-5 mol of Trifluoroacetic Acid)54...

Porter and Spear have reported the mass spectrum of aziridine 8 ) which shows HC=NH+ as the base peak in addition to peaks which correspond to (M—1)+, (M—2)+ and CH3. The mercury sensitized photolysis of aziridine 8 ) gives predominantly ethylene and nitrene. This heteroatom effect does not apply to the mass spectral photochemical correlation for ethylene oxide, which shows very similar behavior in both systems.82)... 

The McLafferty rearrangements is the mass spectrometric analog of the Norrish type II photochemical cleavage of ketones. The relationship between these two processes is easily the most extensively studied of aU mass spectral photochemical correlations. In addition to the well known reaction of aldehydes, ketones, and esters, Eq. (62), many analogous y-hydrogen... 

An illustration of the technological significance of the relaxation phenomenon can be taken from photographic chemistry. Dyes of the cyanine class where Y = S, 0, CH—CH— n = 0,1,2,3...X = haUde, etc, are used as spectral sensitizers to extend photochemical response of the photographic silver hahdes, which only absorb blue and ultraviolet light, into the visible spectral regime. 

The reverse reaction, the photochemical ring opening of sphopyranes (22b), takes place by absorption ia the short-wave uv region of the spectmm and the merocyanine isomer (22a) is obtained. The electron transition of (22a) is ia the visible spectral region, whereas (22b) is colorless. As a result, the dye solution can change from colorless to a colored solution (87,88). These photochromic reactions can be used for technical appHcations (89). 

There are correlations between mass spectral fragmentations and thermal and photochemical fragmentations and rearrangements see Sections 4.02.1.2.1 and 4.02.1.2.2. 

Gonzalez, D. S., Sawyer, A., and Ward, W. W. (1997). Spectral perturbations of mutants of recombinant Aequorea victoria green-fluorescent protein (GFP). Photochem. Photobiol. 65 21S. 

Lecuyer, B., and Arrio, B. (1975). Some spectral characteristics of the light emitting system of the polynoid worms. Photochem. Photobiol. 22 213-215. 

Lee, J., and Seliger, H. H. (1965). Absolute spectral sensitivity of phototubes and the application to the measurement of the absolute quantum yields of chemiluminescence and bioluminescence. Photochem. Photobiol. 4 1015-1048. 

Viviani, V. R., and Bechara, E. J. H. (1995). Bioluminescence of Brazilian fireflies (Coleoptera Lampyridae) Spectral distribution and pH effect on luciferase-elicited colors. Comparison with Elaterid and phengodid luciferases. Photochem. Photobiol. 62 490-495. 

Spectral Transparence Starting from 230 nm HN—< CH3 4-Toluidino p-Naphthoxy Substituent Photoactive from the First Excited Singlet State Polymers Photochemically Active from the First Excited Singlet State of the Phosphorus Substituents - " - "... 

Spectral Transparence Starting from 230 nm 4-Hydroxy-Azobenzene Presence of a Thermally and Photochemically Isomerizable Azo Group Trans-Cis Photoisomerization Photochromism ... 

Phosphorus-containing pesticides la 254 Phosphorus insecticides lb 83 Phosphorus pesticides lb 32 Photochemical activation lb 13 Photochemical reactions lb 15,17 Photodiodes la 24,29 Photo effect, external la 24 -, internal la 24, 29 Photo element la 24,29 Photography, exposure times la 137 -, instmmentation la 137 Photomultiplier la 25ff -, disadvantages la 27 -, energy distribution la 26 -, head on la 27 -, maximum sensitivity la 28 -, side on la 27 -, spectral sensitivity la 28 -, window material la 28 Photocells la 25 Phloxime lb 116... 

The state of research on the two classes of acetylenic compounds described in this article, the cyclo[ ]carbons and tetraethynylethene derivatives, differs drastically. The synthesis of bulk quantities of a cyclocarbon remains a fascinating challenge in view of the expected instability of these compounds. These compounds would represent a fourth allotropic form of carbon, in addition to diamond, graphite, and the fullerenes. The full spectral characterization of macroscopic quantities of cyclo-C should provide a unique experimental calibration for the power of theoretical predictions dealing with the electronic and structural properties of conjugated n-chromophores of substantial size and number of heavy atoms. We believe that access to bulk cyclocarbon quantities will eventually be accomplished by controlled thermal or photochemical cycloreversion reactions of structurally defined, stable precursor molecules similar to those described in this review. 

Direct photochemical reactions in the stratosphere induced by far ultraviolet solar light are well known to be important for the chemistry of the atmosphere. However, only a small fraction of the solar energy flux is in this spectral region. 

Air or water cooled mercury discharge lamps find many uses, one of the more obvious of which is the study of photochemical reactions. These lamps are usually made of vitreous silica because of its low thermal expansion, high melting point and its transparency to ultraviolet radiation. Their operating pressure has a profound effect on the spectral distribution of the radiation produced and therefore it is important to consider the requirements in the design of such lamps. 

Much attention has been devoted to the development of methods to generate quinone methides photochemically,1,19-20 since this provides temporal and spatial control over their formation (and subsequent reaction). In addition, the ability to photogenerate quinone methides enables their study using time-resolved absorption techniques (such as nanosecond laser flash photolysis (LFP)).21 This chapter covers the most important methods for the photogeneration of ortho-, meta-, and para-quinone methides. In addition, spectral and reactivity data are discussed for quinone methides that are characterized by LFP. 

The observed spectral changes suggest the following photochemical cross-linking mechanism for oligoorganoepoxystannanes ... 

However, examination of the spectral properties of the starting ketones and isolated photoproducts indicated that the product distribution was determined by the photochemical properties of the molecules rather than their relative thermodynamic stabilities. These workers proposed that these... 

The rate of photolytic transformations in aquatic systems also depends on the intensity and spectral distribution of light in the medium (24). Light intensity decreases exponentially with depth. This fact, known as the Beer-Lambert law, can be stated mathematically as d(Eo)/dZ = -K(Eo), where Eo = photon scalar irradiance (photons/cm2/sec), Z = depth (m), and K = diffuse attenuation coefficient for irradiance (/m). The product of light intensity, chemical absorptivity, and reaction quantum yield, when integrated across the solar spectrum, yields a pseudo-first-order photochemical transformation rate constant. 

Andersson, P.O., T. Gilbro, and L. Fergusson. 1991. Absorption spectral shifts of carotenoids related to medium polarizability. Photochem. Photobiol. 54 353-360. 

The mass spectral fragmentation of the adducts (72), (73), and (78) occurs by the loss of ketene from the molecular ion, and in accord with this and the results of other research groups 119-122>, both (72) and (73) form ketene and (79) both thermally and photochemically. 

Photochemical changes in both II and the acetoxy derivative have been monitored in fluid solution and incorporated in a polymer film. Fig. 5 shows the spectral changes accompanying photochemical transformation of the acetoxy derivative. Then changes may be interpreted in terms of scheme 3, which proposes a photochemical 1,3 acyl shift to form "in situ" an ultraviolet stabilizer chromophore which also has a carbonyl functionality. 

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