Quantum Yields of Free Radicals in Nonviscous Solutions

1 Quantum Yields of Free Radicals in Nonviscous Solutions 

The quantum yield of the formation of free radicals 0 jiss in the photodissociation step is an important characteristic of a PI. A large family of Pis manufactured by Ciba Additives under the names Irgacure and Darocur have a benzoyl fragment in their molecular structure  

These molecules have a high quantum yield for the formation of their triplet state and usually rapidly dissociate into free radicals in the triplet state undergoing 

This is termed the Norrish I type process for ketones.  

There can be a substantial difference in the reactivity of n,n and n,n excited triplet states in a-cleavage. These differences are experimentally characterized by Tj (triplet lifetime) or (the dissociation rate constant) for a-cleavage. In general, aromatic ketones with n,n lowest triplet states undergo much faster a-cleavage and have shorter triplet lifetimes than ketones with n,n states. The latter may be dubbed inefficient PIs.  

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