Cryogenically Flexible Organic Single-Crystal Heterostructures via Molecular Alloying for Advanced Optical Tuning

Organic single-crystal heterostructures (OSCHs) constitute a promising platform for advanced flexible optoelectronics, yet imparting mechanical flexibility to these multiblock systems, especially given the susceptibility to failure at the interfaces between individual crystal segments, remains challenging. This obstacle is particularly aggravated at cryogenic temperatures, where the freezing of vibrational motion may cause brittleness and lead to mechanical failure. Herein, we describe an epitaxial growth strategy using molecular alloys for the fabrication of crystals of cryogenically flexible two-color (blue–cyan–blue) triblock heterostructures, prepared by growing triphenylene (TP) segments onto perylene (PER)-doped alloy seed crystals via crystallization under controlled cooling. The compatibility between the host and guest molecules provides interfaces with low defect densities. Analysis of the crystal structure reveals an abundance of weak intermolecular interactions that are thought to enable the reversible elastic deformation observed at both 298 and 77 K, thereby preventing cracking. Simultaneously, efficient Förster resonance energy transfer (FRET) between TP and PER enables continuous emission tuning and doping-ratio-controlled programmability of the optoelectronic properties. The resulting heterostructures not only support low-loss active optical waveguiding and programmable multichannel optical logic and information encoding but also remain fully operational for optical transduction during bending under cryogenic conditions. This work establishes a general molecular alloying approach to structures that integrate low-temperature mechanical compliance with sophisticated photonic functionalities, providing a pathway to deformable, multiemissive optoelectronics elements that remain operational in extreme environments.