Strong Aggregate Emission of Perylene Diimide in Solid State Enabled by Polymerization-Mediated Charge Transfer

The molecular engineering of fluorescent organic/polymeric materials, specifically those emitting in the deep red to near-infrared spectrum, is vital for advancements in optoelectronics and biomedicine. Perylene-3,4,9,10-tetracarboxylic acid diimide (PDI), a well-known fluorescent scaffold, offers high thermal and photophysical stability but suffers from fluorescence quenching in solid or aggregate states due to intense π-π interactions. To mitigate this, simple and versatile methods for strong PDI aggregate emission without extensive synthetic demands or adverse effects on photophysical properties are highly desirable but still lacking. In this study, we report a straightforward strategy to enhance the solid-state emission of PDI by introducing through-space charge transfer (TSCT) via controlled radical polymerization, which can efficiently distort the typical face-to-face PDI stacking, enabling greatly enhanced deep red emission. This is achieved by growing electron-donating star-shape styrenic (co)polymers from a multidirectional electron-accepting PDI initiator. A photoluminescent quantum yield of up to 45% in solid films was realized, at emissions wavelengths ranging from 625 to 655 nm (1.89–1.98 eV). The incorporation of polycyclic aromatic monomers further shifted the emission into the near-infrared region, albeit with a reduced intensity. Overall, the emission of the PDI-based TSCT polymers can be systematically manipulated by leveraging the balance between PDI stacking and the TSCT degree, as confirmed by both experimental study and theoretical calculations. Our approach circumvents complex synthetic procedures, offering highly emissive materials with large Stokes shifts and showing broad potential for optoelectronic technology.