Protection of densely populated excited triplet state ensembles against deactivation by molecular oxygen.

This critical review discusses different approaches towards protection of photoactive materials based on triplet excited state ensembles against deactivation by molecular oxygen though quenching and photooxidation mechanisms. Passive protection, based on the application of barrier materials for packaging, sealing, or encapsulation of the active substances, which prevent oxygen molecules from penetration and physical contact with excited states and active protection, based on the application of oxygen scavenging species are compared. Efficiencies of different approaches together with examples and prospects of their applications are outlined.