Past exam of the chemistry course of the year 3 of the natural sciences course of the University of Cambridge / 2022 / Paper 2A / Section A / 16 / c

A quencher-independent intersystem-crossing rate adds to the unquenched decay rate:The normalized Stern-Volmer equation retains the same form, so intersystem crossing does not bias $k_Q$ if the actual unquenched lifetime is used. It reduces ${\varphi }_0$ below one and changes the slope through ${\tau }_0$; assuming ${\tau }_0=1/k_F$ would then give the wrong result. A quencher that itself changes intersystem crossing or returns triplet population to the singlet requires a larger kinetic scheme.