Influence of the atmosphere on the phosphorescence of a brominated diphenylphosphine oxide–ethyl naphthaleneimide dyad

The molecular dyad diphenylphosphine–ethyl bromine naphthaleneimide (Br-DPPENI) emits strong fluorescence and phosphorescence. We studied the intensity and lifetime of the phosphorescence of Br-DPPENI embedded in PMMA films in atmospheres of air, He, Ar, N₂, and O₂ as a function of pressure between vacuum and ambient pressure (1 bar). The experiment was performed in the frequency domain with a two-channel lock-in amplifier, and the data were analyzed with the polar plot or phasor technique. Reversible shortening of the lifetime due to triplet–triplet annihilation was found in the presence of atmospheric or pure oxygen. With small modulation frequencies, an additional slow component of the phosphorescence dynamics is observed, which is ascribed to the diffusion of oxygen into the sample films.