Red and Near-Infrared Emissive Organic Crystals: Molecular Design and Optoelectronic Applications

Red-emissive organic materials play a pivotal role in optoelectronics, including displays, optical communications, organic lasers, and biomedicine, owing to their high penetration and low scattering properties. However, conventional polymer and thin-film emitters often face efficiency losses at long wavelengths and limited operational stability. Organic molecular crystals have emerged as promising alternatives by offering high purity, low defect density, and unique optical anisotropy. Among them, red-emissive organic molecular crystals (ROMCs) remain relatively underdeveloped compared to their blue and green counterparts. Moreover, the inherent brittleness of most crystals poses significant challenges for their integration into flexible and wearable devices. This review highlights recent advances in the design and development of ROMCs, emphasizing molecular and crystal engineering strategies to overcome photophysical limitations and impart mechanical flexibility. Emerging applications in organic lasers, optical waveguides, and bioimaging are discussed, alongside key challenges and future research directions. By bridging fundamental understanding and practical deployment, this perspective offers a comprehensive roadmap for the rational design of flexible, red-light-emitting crystalline materials for next-generation optoelectronic platforms.