Highly Polarized Red Emission From Organic Semiconductor Single Crystals

Organic semiconductor single crystals (OSSCs) represent ideal platforms for intrinsically polarized light emission, holding immense promise for stereoscopic displays, quantum communication, and biomedical sensing. However, realizing highly polarized emission in the long‐wavelength red regime from OSSCs remains a formidable challenge. Here, we reveal that intrinsic polarization‐red emission in OSSCs is governed by the synergistic interplay between molecular anisotropy and supramolecular packing. We establish a unified design strategy that integrates three critical elements: a linear π‐conjugated backbone with a high aspect ratio, supramolecular architectures that enforce horizontal alignment of transition dipoles, and donor‐acceptor engineering tailored for targeted spectral red‐shifting. Guided by these principles, we identify 2,7‐bis(4‐methoxyphenyl)‐9 H ‐fluoren‐9‐one (BMeOPhFO) single crystals as a model emitter, delivering highly intrinsically polarized red emission with a record photoluminescence polarization ratio (PR) of 97.4. Linearly polarized light‐emitting diodes fabricated using BMeOPhFO single crystals achieve a remarkable electroluminescence PR of 62.7. Furthermore, by incorporating a semi‐transparent electrode to construct an optical microcavity, we enhance the PR to 228.1 while narrowing the emission linewidth to a full width at half maximum of 7.8 nm. This work provides robust design guidelines for achieving highly polarized long‐wavelength emission in OSSCs, paving the way for next‐generation polarized optoelectronic devices.