Synthesis, characterization and photophysical properties of benzil-labelled polymers for studies of diffusion-limited interactions by phosphorescence quenching

A new technique for synthesizing benzil-labelled polystyrenes has been developed. This new procedure has advantages over an older synthesis by Horie and Mita in that it involves fewer and less complicated synthetic steps. In addition, the new synthetic pathway should allow for labelling of different sites on the polymer chain and for labelling of different polymers such as poly(methyl methacrylate). The phosphorescence lifetime of terminally benzil-labelled polystyrenes in cyclohexane was found to be approximately 85-90 μs at 25°C with the concentration of benzil at 10^-5 M and was independent of labelled polystyrene molecular weight and polystyrene concentration up to 150gl^-1. When used in phosphorescence quenching studies, these materials were found to exhibit non-single-exponential lifetimes in the presence of anthracene and azulene quenchers for a concentration of benzil label ≤10^-4 M. An explanation for this anomalous behaviour and a technique for decoupling these decays into two lifetimes has been proposed. This technique should allow for the study of diffusion-limited interactions occurring in higher-molecular-weight polymer systems where the label concentration ≤ 10^-4 M.