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

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.