Excited-state lifetimes intramolecular radiationless

The results obtained are discussed on the basis of a postulated mechanism which consists of a number of elementary transformations (steps), each of which is characterized by a rate constant [33]. In the relation between the experimental and mechanistic quantities, the experimental data generally appear as ratios of the value obtained in the absence of the quencher to the value obtained in the presence of a given amount of quencher. Consider for example the very simple scheme of figure 1, where k,., and k are first order rate constants for luminescence, intramolecular reaction and radiationless deactivation of the excited state, and k is the second order rate constant of the quenching reaction. In the absence of the quencher B the lifetime of the excited state is given by... 

The various rate constants are indicated beside the corresponding arrows. kj, kg and are the first-order rate constants for radiationless deactivation of the excited state, photonic emission and intramolecular chemical transformation respectively. The intrinsic lifetime Tq of the excited state Ais ... 

In Sections 7.3 and 7.4, the temperature dependence of radiationless transitions and the effect of deuteration on the lifetimes of excited electronic states are examined. In Section 7.5, a contribution to time-resolved spectroscopy is presented. In that section, we will discuss a problem dealing with transport phenomena of electronic excitations in doped molecular crystals. The theory of singlet excitation energy transfer uses an effective Hamiltonian to account for intramolecular excited-state depopulation and energy transfer by multistep migration among guest molecules. 

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