Polymorph-tuned photoinduced red luminescence and room-temperature phosphorescence in macrocyclic molecular crystals

Despite the increasing demand, fabricating organic functional molecular crystals with highly tunable photoluminescent properties in the same system remains a significant challenge. Here, we demonstrate that photoinduced red emission and room-temperature phosphorescence (RTP) can be effectively regulated via crystal-polymorph modulation in a macrocyclic diphenylamine[3]arene (DPA[3]) compound. During crystal growth, kinetic control directs DPA[3] molecules to adopt distinct stacking motifs, resulting in two polymorphs (Type A and Type B) with divergent luminescent properties. Type A crystals exhibit photoinduced red emission extending to 630 nm, while Type B crystals show long-lived green RTP (lifetime >450 ms) after ultraviolet light excitation. Notably, thermal treatment of Type A crystals induces a partial polymorphic evolution toward the Type B crystals. Experimental and calculation analyses reveal that paired DPA[3] molecules in Type A form a columnar packing motif, which may facilitate photoinduced electron transfer to generate charge transfer intermediates for red luminescence. In contrast, Type B crystals feature a more distorted herringbone stacking motif with a tighter molecular stacking structure, enabling stabilizing triplet excitons that support efficient RTP. Our findings present an effective strategy for achieving single-component materials with multiple luminescent functionalities by regulating the aggregate state. Molecular crystals with luminescent properties are desirable, but tuning of properties within one system is challenging. Here, the authors report crystals with photoinduced red emission and room temperature phosphorescence regulated by polymorph modulation.