Analysis of singlet oxygen transport from air to surface by phosphorescence-slope inflection angle (SIA) approach

Singlet oxygen (¹O₂) is a reactive species that plays a role in environmental and biological surface chemistry; however, the mechanisms of the association of airborne ¹O₂ at the air/surface interface are poorly known. Here, we help resolve this problem using ¹O₂'s near-infrared (NIR) phosphorescence and geometric analysis based on the slope inflection angle (θ) of air-to-particle transfer. This offers insight into ¹O₂-surface binding as opposed to conventional kinetic analysis. Two 9,10-disubstituted anthracene quenchers were adsorbed to the particle surface, producing θ ranging from ~91° (greater quenching) to ~99° (less quenching) due to the reduction of airborne ¹O₂ lifetime (τ_airborne) by 43% to 95%. A more efficient (lower θ) ¹O₂ quenching is observed in the order dimethylanthracene-coated particle > anthracene dianion-coated particle > native silica. The anthracene dianion charges and surface silanols did not enhance the ¹O₂ surface quenching. Indeed, the quenching of airborne ¹O₂ by native silica was minimal, in which a slight reduction in its surface lifetime (τ_surf) was observed (0-5%). This θ approach opens up opportunities in fields such as surface oxidation processes in nanoplastics, which is an emerging concern.