Cryogenically Flexible Phosphorescent Organic Crystals that Transmit Self-Sustained Persistent Luminescence with Spatiotemporal Control.

Abstract

Concomitant long-lived phosphorescence and cryogenic elasticity in soft matter is an immensely challenging endeavor due to the contrasting effect of low temperatures on these properties. While the low temperature normally extends and enhances phosphorescence, it typically compromises mechanical elasticity by freezing the molecular motion, inevitably leading to brittleness and cracking of soft materials. In this work, we posit that the emerging class of organic crystals can overcome this intrinsic disparity and describe an organic crystalline material that meets both requirements─an exceptional elasticity of its crystals at 77 K and ultralong afterglow of up to about 30 s, the longest lifetime of a flexible organic crystal reported to date. The material, triphenylene, was prepared as elastic crystals, where the molecular rigidity and dense packing enable reversible lattice deformation and mechanical robustness on cooling, while they also result in prolonged phosphorescence at low temperatures. Crystals of this material act as dynamic phosphorescent waveguides, with their emission persisting in low temperatures and dark, demonstrating both sustained signal transmission capabilities and a unique opportunity for spatiotemporal control of the optical output. At a conceptual level, the results introduce organic crystals for time-encoded biological information transmission, providing a novel material platform for flexible, lightweight optical devices and sensors that can function in extreme environments.