Polarized light, photochemistry

F. Dorr, Polarized light in spectroscopy and photochemistry . Reference T. Excited State Geometries... 

Stumpe and co-workers [50] have investigated the photochemistry of SCLC poly(olefin sulfone)s such as 20 and a copolymer with the same main chain but with 95% of the cinnamate groups replaced with saturated tetradecyl groups. As cast or heat-treated thin films of the polymers were irradiated at 313 nm using both nonpolarized and linearly polarized light. Initial irradiation led to an initial increase in the absorbance of the films at 280 nm followed by a decrease. The... 

Artificial myoglobins prepared with modified and metalloporphyrins. Biochemistry, 9,2268-2275. Dorr, F. (1971). Polarized light in spectroscopy and photochemistry, in A.A. Lamola (ed.), Creation and Detection of the Excited States, pp. 53-122, Dekker, New York. 

Buchardt O (1974) Photochemistry with circularly polarized light. Angew Chem Int Ed Engl 13 179-185... 

Direct Asymmetric Photochemistry with Circularly Polarized Light... 

Asymmetric photochemistry with circularly polarized light (CPL), based on NCD, is well-established and has been extensively reviewed [25,26]. The Cr(III)tris-... 

Polarized light absorption orients both isomers of photisomerizahle chromo-phores, and quantified photo-orientation both reveals the symmetrical nature of the isomers photochemical transitions and shows how chromophores move upon isomerization. Photo-orientation theory has matured by merging optics and photochemistry, and it now provides analytical means for powerful characterization of photo-orientation by photoisomerization. In azobenzenes, it was found that the photochemical quantum yields and the rate of the cis—>trans thermal isomerization strongly influence photo-... 

Rau, H., Direct Asymmetric Photochemistry with Circularly Polarized Light. In Inoue, Y., Ramamurthy, V. (eds), Chiral Photochemistry, Vol. 11, Marcel Dekker, New York, 2004, pp. 1 44. 

The gas phase photochemistry of acetic acid has been studied by ab initio methods. The photochemical decomposition of aliphatic amino acids using circularly polarized light has been reported. Many examples were cited. A typical result is shown in Scheme 3 for the decomposition of valine in aqueous HCl solution. Pyrene has been established as the most effective polycyclic arene sensitizer for the photochemical decomposition (irradiation at 366 nm) of N-phenylglycine. The introduction of electron-donating groups into the aryl ring of the glycine also enhances the rate of decomposition. ... 

Photochemistry induced by circularly polarized light has been shown to make possible both partial chiral resolution and racemization of rhodamine 69. It has been found that the rate of racemization can be measured for rapidly inverting molecules of these types in achiral solvents. 

RRKM calculations on triplet species in diazirine photolysis,647 BEBO calculations on the activation energies for hydrogen-transfer reactions,648 stereochemistry as a probe for photochemical reaction mechanisms,649 photochemistry with polarized light,550 dimer formation,651 the formation of molecular complexes,552 hydrogen bonding in electronically excited states,553 and the interactions between excited-state aromatic molecules and 02654 have been the subjects of recent theoretical treatments. 

Interest in aromatic chemistry continues at the same high level as in recent years. Substitution and cyclization processes are two areas which have attracted considerable attention over the past year. Pertinent here, as elsewhere in this volume, are the reviews on photochemistry with circularly polarized light by Buchardt,1 and the photochemistry of carbonium ions by Cabell-Whiting and Hogeveen.2 Current literature describing light-induced reactions of pyrroles has also been briefly reviewed.8... 

This chapter focuses on this particular family of photochromic systems. As presented elsewhere in this book, azobenzene-containing materials experience reorganizations at different length scales in response to light of the appropriate wavelength. The photochemistry of azobenzene molecules will be described. The main types of azobenzene polymeric architectures will be presented as well as associated synthetic methods. A brief overview of the photoresponse of azobenzene polymers when exposed to linearly polarized light in their absorption bands will be presented. Special emphasis will be... 

I.r. laser techniques have been used to study [Fe(CO)4] in a nitrogen matrix at 20 K. Surprisingly, the quantum yield for intramolecular isomerization is greato-than the quantum yield for formation of [Fe(CO)4(N2)]. Photolysis of matrix isolated [Mo(CO)s] in the presence of Na at 20 K affords [Mo(CO)5Na)]. Under similar conditions, the analogous chromium and tungsten complexes have been detected by i.r. and Raman techniques. The photochemistry of [O(C0)5] and related species in matrices has been studied via polarized light spectroscopy. A mechanism has been proposed which accounts for almost all the experimental data on matrix-isolated [M(CO)s] (M=Cr, Mo, or W), [M(CO)5(Na)], and [M(CO)4(CS)]. Reactions occur via the following steps ... 

The essentials of a quantum mechanical treatment of the interaction of electromagnetic radiation with molecules is described in the first chapter, and the second one deals with supramolecular photochemistry, with particular emphasis on energy and electron transfer with a description of the Marcus theory. The following chapters are devoted to the different photochemical and photophysical techniques spectrophotometry and spectrofluorimetry, actinometry, absorption and luminescence techniques with polarized light excitation, time-resolved absorption and luminescence spectroscopy, down to femtosecond resolution. Each... 

The fundamental measurement in photochemistry/femtochemistry is the measurement of the yield Y per absorbed photon for the photochemical reaction (or equivalently cross section ), often as a function of optical wavelength ha>, absorbed optical fluence Fa, angle of incidence of the light to the surface d, and polarization of the light relative to the surface normal , i.e., as Y hot),FOJ,6i,POJ). A good indicator for hot electron (or more generally hot carrier) induced photochemistry is when the variation of (/ , ()i, ) parallels that for absorption of the light in the metal substrate. Direct adsorbate photochemistry behaves quite differently when the transition dipole is perpendicular to the surface [129]. There is, however, some... 

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