Photochemical and photophysical properties

The photochemistry of transition metal 1,3-diketone chelate complexes has been known for some time [30,31], and their photophysical and photochemical properties and photocatalytic activity in different chemical reactions were reviewed in 1990 by Marciniak and Buono—Core [32]. Further discussion on the photochemistry of meta] chelate will not take place here since this subject is out of the scope of this chapter. 

Redox participants are chosen to facilitate spectroscopic, biochemical and electrochemical probing of DNA CT. These include metallointercalators, organic intercalators, and modified bases that possess useful, well-described, and varied redox, photophysical and photochemical properties (Table 1). Our probes are readily incorporated into DNA assemblies where CT distances ranging from 3.4 to 200 A and driving forces spanning over two volts can be modulated with certainty. Most importantly, all redox probes which afford fast and/or efficient CT through DNA are well-coupled to the 7r-stack. 

In Chapter 2 we discussed a number of techniques used to study the various photophysical and photochemical processes occurring in anthracene and similar molecules. In that discussion we were primarily interested in the singlet state. In this chapter we will discuss some of the techniques available for studying the photophysical and photochemical properties of the triplet state. Most of our discussion will be directed to the photochemistry of simple ketones. 

Foote, C.S. Photophysical and Photochemical Properties of Fullerenes. 169,347-364 (1994). Fossey, J., Sorba, J., and Lefort, D. Peracide and Free Radicals A Theoretical and Experimental Approach. 164, 99-113 (1993). 

The scientific group from Turkey62 studied photophysical and photochemical properties and behaviour of an azlactone derivative, 4-(p-N,N - dimethylaminophenylmethylene)-2-phenyl-5-oxazolone in sol-gel... 

With the aim of mimicking, on a basic level, the photoinduced electron-transfer process from WOC to P680+ in the reaction center of PSII, ruthenium polypyridyl complexes were used (182-187) as photosensitizers as shown in Fig. 19. These compounds are particularly suitable since their photophysical and photochemical properties are well known. For example, the reduction potential [Rum(bpy)3]3+/-[Run(bpy)3]2+ (bpy = 2,2 -bipyridine) of 1.26 V vs NHE is sufficiently positive to affect the oxidation of phenols (tyrosine). As traps for the photochemically mobilized electron, viologens or [Co(NH3)5C1]2+ were used. 

Foote CS (1994) Photophysical and photochemical properties of fullerenes. Top Curr Chem 169 347-363. 

Based on a large body of experimental and theoretical work, the following rules have been found most important in obtaining desirable photophysical and photochemical properties of transition metal complexes. 

Fullerene Ceo is an electron-deficient compound with rich photophysical and photochemical properties. Moreover, the triplet-excited state of Ceo is formed almost quantitatively and, in the presence of molecular oxygen, energy transfer from the triplet-excited... 

By using high intensity flash lamps and laser sources, photophysical and photochemical properties of the triplet states can be studied. These sources also help to study emission from upper excited state. 

For these reasons, and the relative ease with which the complexes are prepared, an increasing number of studies have been performed on the photophysical and photochemical properties of such complexes. Though most of the studies in this area have been performed on dinuclear ruthenium complexes, an increasing number of Ru/Os and Os/Os dimers have been studied in recent years (228, 541-552) and this subject has been reviewed (222). 

The three forms of Pr differing in molecular weight exhibit very similar photophysical and photochemical properties [7,113,114], regarding the shape of the stationary red fluorescence and excitation spectra, the triexponential emission decay function and its component composition, the emission parameters (cf. tJ, 3>f(expti.corr) cf- also Aussenegg et al. [139]), the heat release (a) by the P and I700 species, and the total photochemical quantum yield ( r-/r) (Table 1). 

The insensitivity of so many of the photophysical and photochemical properties to proteolytic degradation down to about half of the original molecular weight is remarkable. It is particularly noteworthy when the location of the bilatriene chromophore near the N-terminus—one of the sites of preferential endogenous proteolytic attack—is taken into account and also the fact that the photochromic behavior of chromopeptides obtained by further protein degradation progressively deteriorates and is eventually lost [8b],... 

Hybrid Orbitals. Orbitals, as one-electron energy levels, and corresponding wavefunctions are mathematical concepts only states are physically observable. Nevertheless, the simple picture of orbitals as the rungs of an energy ladder is very helpful, and is in many cases sufficient to account for the photophysical and photochemical properties of molecules. In more accurate pictures of orbitals it is necessary to consider their interactions, as they are not really totally independent. In this respect the concept of hydrid orbitals is important such hybrid orbitals are formed from a combination of elementary orbitals defined by their quantum numbers n, /, and m. The best... 

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