Molecular Oxygen in Organic Luminescent Adlayers: Coupled Sorption, Diffusion, Excited-State Quenching, and Recovery

Organic luminescent adlayers are versatile platforms for oxygen sensing. Their optical responses can be tuned through molecular structure, excited-state pathway, host environment, solid-state packing, and film morphology. In such adlayers, however, the film-level emission response cannot be ascribed to any single parameter. External oxygen partial pressure, local oxygen concentration, and intrinsic bimolecular quenching efficiency each contribute. Oxygen must first partition from the gas phase into the adlayer and diffuse through morphology-dependent pathways. It then reaches oxygen-accessible luminescent sites and quenches short- or long-lived excited states. During recovery, it diffuses back to the interface and desorbs. This review surveys these coupled processes, focusing on the physical chemistry that links external pO2to the local oxygen concentration near luminescent sites. We contrast the typically modest oxygen response of short-lived prompt fluorescence with that of longer-lived and triplet-involved emissive pathways, and examine how microheterogeneity, nonlinear Stern–Volmer behavior, and photooxidation complicate film-level calibration. By coupling sorption, diffusion, excited-state quenching, and recovery, this review provides a physically grounded basis for designing and assessing reversible, reproducible, and application-specific oxygen-sensing luminescent films.