Photoelectron and Triplet Energy Transfer

Triplet excited state quenching by photoelectron transfer (PET) and energy transfer (ET) play a central role in biological photosynthesis, visual transduction, organic photochemistry, semiconductor photocatalysis and imaging. PET and ET across the insulating walls of a hemicarcerand have recently been studied in order to improve our understanding of these photophysical processes.  

Equations 9.1 and 9.2 schematically describe energy and electron transfer quenching of an incarcerated triplet excited state HostOG(Tl) with a bulk phase quencher Q  

ET proceeds by a Dexter electron exchange mechanism and is a weakly coupled non-adiabatic process. Its rate constant kET can be approximated by the Golden Rule  

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The charge transfer transitions are expected to be mainly L —> M ttu - ( + l)s and % (n+ l)p. The experimental ionization potential of acetylene is 11.41 eV, both vertical and adiabatic since the first vibronic band in the photoelectron spectrum is also the most intense The asymptotic charge transfer energies are then the difference between this IP and appropriate EA of each metal ion, and are the same for both triplet and singlet electronic states. These are tabulated in Table 20. 

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