Photophysical steps quenched

As in the case of photoisomerisations, the reaction can proceed either via the singlet or the triplet intermediate. The component B is part of the reaction in contrast to the sensitisation mechanism discussed above. In addition both pathways via the singlet or triplet state can be quenched. The photophysical steps are summarised in Table 3.2 and the reaction scheme is derived in Appendix 6.6.1.1. In the following examples this information is used to derive the time laws and the quantum yields for 4 types of photoaddition reactions according to either the normal addition reaction... 

Besides the given mechanism the stationary concentration of the excited photophysical intermediate is influenced in contact with a partner B. Energy transfer to an acceptor molecule B opens a new reaction channel, but does not form a new reaction product itself. Looking at the photoisomerisation, this energy transfer will reduce the concentration of the excited state. By this step the photoreaction is desensitised or quenched. This quenching can either happen in the singlet state A or at the triplet state A". Both mechanisms are discussed in the following examples. 

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