Broad‐Band Visible‐Light Excitable Room‐Temperature Phosphorescence Via Polymer Site‐Isolated Dye Aggregates

Abstract Organic room‐temperature phosphorescent (RTP) materials are useful in optical imaging and sensing technologies. However, most organic phosphors, including red‐light emitting dyes, exhibit unusually large Stokes shifts, and require excitation with ultraviolet radiation, the high energy of which can induce substantial photo damage. Here a design concept of using dihydroxy‐functionalized naphthalenediimide (NDI, λ_abs < 400 nm) is demonstrated to initiate ring‐opening polymerizations of L‐lactide (PLA) and ε‐caprolactone (PCL), resulting in a linear polymer NDI‐PLA2/NDI‐PCL2. With the right combination of substituents, the design simultaneously realizes broadband visible light absorption (λ_abs = 450–650 nm) and near‐infrared RTP (λ_RTP = 700 nm) with millisecond‐long lifetimes. Polymer site isolations of the aggregation‐prone NDI phosphors may prevent aggregation‐caused quenching of RTP common in bulk, by forming various microscopic ground‐state aggregates, which exhibit triplet‐emitting states lower than that of the individual phosphor. The method can potentially be expanded onto other molecular RTP systems.