Recent progress in luminescent liquid crystal materials : design, properties and application for linearly polarised emission

Luminescent liquid crystal (LC) materials have attracted significant interest for organic optoelectronic applications, especially for linearly polarised emission, because of their combination of ordered alignment and luminescence property. Since the first demonstration of polarised organic light-emitting diodes (OLEDs) in 1995, remarkable progress has been made with polarised electroluminescence because of the continuous advances in the design of suitable LC materials. In this Review, we summarize luminescent LC materials with representative examples based on fluorescent materials, phosphorescent materials, and lanthanide complexes. The structure-property relationships for polarised emission and, when available, electroluminescence of these materials are presented and discussed, with a focus on phosphorescent metallomesogens. We also present the rationale behind the design and development of luminescent LC materials for high efficiency polarised OLEDs, along with the challenges ahead to achieve efficient devices.