The active role of excited states of phenothiazines in photoinduced metal free atom transfer radical polymerization: singlet or triplet excited states?

Abstract

The active role of phenothiazine excited states in photoinduced metal-free atom transfer radical polymerization (ATRP) was investigated by using laser flash photolysis, fluorescence, phosphorescence and electron spin resonance spectroscopy. Weak fluorescence emission and short lifetimes of the singlet excited state (2.01 ns) together with high intersystem crossing quantum yields (∼0.6) and long triplet lifetimes (40 μs) indicate efficient intersystem crossing into the triplet state and its dominant role in a degenerative electron transfer process in photoinduced metal free ATRP.