Quantum yield defined

The efficiency of a photochemical reaction is expressed in terms of quantum yield ( ) defined as... 

The bis(aryl)azide sensitizers must be soluble in the resin, thermally stable, and sensitive to the desired wavelength of light. A commonly used compound is 2,6-bis(4-azidobenzylidene)cyclohexanone, which absorbs at 360 nm (see structure). Conjugation extension and other structural changes can shift the absorption maximum to longer wavelengths and allow access to the other mercury lines at 405 and 436 nm. A number of bis(aryl)azides are efficient photosensitizers (21). Quantum yields, defined as the number... 

The relative fluorescence quantum yield defined in Eq. (3.8) is the ratio of the stationary singlet excitation concentration in the presence of quenchers to the same concentration in their absence. By substituting into this definition N from Eq. (3.654a), we confirm that the fluorescence quantum yield obeys the Stem-Volmer law (3.363) with the same constant as in Eq. (3.364), but with the contact [Pg.339]

The existence of large quantum yields in certain photochemical reactions constitutes the most direct evidence for chain reactions. The quantum yield, defined as the number of molecules reacting for each photon of radiation absorbed, will be discussed in a later chapter where the matter of photochemical chains will be presented in more detail. 

The last decade of the twentieth century has been revolutionary in the study of molecular electron transfer processes. For the preceding century scientists have investigated three types of such processes transfer between a donor and an acceptor species, transfer between two sites on the same molecule and transfer between a molecular species in solution and a metal or a semiconductor electrode. The main observable in such studies is the electron transfer rate, though in studies of photoinduced electron transfer processes the quantum yield, defined as the number of electrons transfeiTed per photon absorbed, is also a useful observable. The invention of the tunneling microscope and later experimental developments have now made it possible to investigate another manifestation of electron transfer electronic conduction by a molecule connecting two bulk metal or semiconductor electrodes. In this... 

The quantum efficiency (p defined as the ratio of the number of electrons transferred across the interface, and of the number of photons absorbed by the adsorbed dye layer, is not easy to determine. This is on account of the problems of measuring the light absorption by one monolayer or separating it from the absorption by the dye solution. Therefore, many scientists prefer to give values of a quantum yield, defined as the number of injected electrons per incident photons which is easy to measure. These two quantum yields are related by the equation... 

This result simply due to the dielectric boundary conditions imposed on the radiated field of a molecule at the interface. Here 1/Tnr and 1/Tril<1 are the non-radiative and the radiative rates, respectively. The quantity in the brackets accounts for the proximity of the interface at a distance z from the molecule. Algebraic expressions for the weighting functions L zyL and LyfylL are known [114] and depend on z and the refractive index ratio of the two materials that form the interface. The parameter 6t is the angle enclosed between the emission dipole moment and the surface normal. The weighting functions approach unity for z > A. For a molecule adsorbed on a PMMA surface in air, the lifetime should be 2.7 times longer when its emission dipole moment is perpendicular to the interface than when it lies in the surface. Also, the fluorescence quantum yield, defined as = 1 — (t/ rnr), is affected by the location and orientation of the molecule. 

In every free radical experiment, you want to know the concentration of free radicals you have generated. In photochemistry, the yield of a species X is expressed by the quantum yield, defined as the number of species X formed per photon absorbed by the sample ... 

All the quantum yields defined so far cannot give a correct view of the photokinetics. light absorbed during the photoreaction changes and the photochemical process can combine more than one step of photochemistry. 

In photochemistry, the most important reaction parameter is quantum yield defined as... 

Synthetic quantum yield defined by Equation 26.4. Wavelength of light, m. 

Assuming all of the input energy could be used for photochemistry, it is apparent that an efficiency or quantum yield (defined as the number of molecules per photon undergoing change) of better than 0.3 is required in order to write information. Such quantum yields for photochemical reactions would be considered unusually high in the solid state. 

The quantum efficiency (or quantum yield) — defined as the probability that a particular type of event of photobiological or photochemical interest occurs as the result of absorption of a photon — should be independent of wavelength. 

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