Measuring Cumulative Exposure to Oxygen with a Diphenylphosphine-Alkyl Naphthaleneimide Luminescence Turn-On Dyad

2-(2-Diphenylphosphanylethyl)benzo[de]isoquinoline-1,3-dione is a poorly luminescent, photoinduced-electron-transfer (PET) dyad, NI-(Ph)₂P:, in which the luminescence of its naphthaleneimide (NI) part is quenched by the lone-pair electrons of the phosphorus atom of the (Ph)₂P: group. Photoinduced oxidation of (Ph)₂P: to (Ph)₂P=O by molecular oxygen regenerates the luminescence of the NI group, because the oxidized form (Ph)₂P=O does not serve as a quencher to the NI system. The oxidation of (Ph)₂P: is thermally inaccessible. The NI-(Ph)₂P: system was applied to monitoring the cumulative exposure of oxidation-sensitive goods to molecular oxygen. The major advantage of this new PET system is that it reacts with oxygen only via the photoinduced channel, which offers the flexibility of monitoring the cumulative exposure to oxygen in different time periods, simply by varying the sampling frequency. Electronic-energy calculations and optical spectroscopic data revealed that the luminescence turn-on upon reaction with molecular oxygen relies on a PET mechanism.