Formulation of a Composite System of Liquid Crystals and Light-Emitting Semiconductor Quantum Rods : From Assemblies in Solution to Photoaligned Films

The ability of strongly emitting semiconductor quantum rods (QRs), when macroscopically aligned, to emit linearly polarized light makes them the perfect candidate for liquid crystal (LC) display backlights. Macroscopic QR ordering is previously demonstrated by photoalignment of QR composites with polymerizable LC monomers. In this study, it is demonstrated that the optimum concentration of LC monomers and core/shell CdSe/CdS QRs enabling someone to achieve their uniform homogeneous orientation in photoaligned films strongly depends on the lengths and aspect ratios of the QRs. By aligning QRs with different aspect ratios ranging from 3 to 10, the best performance is achieved for shorter QRs with lengths of 11 and 31 nm as compared to longer QRs with a length of 50 nm. While high-aspect-ratio QRs are expected to show higher emission anisotropy, formulation of such QRs in composite films is challenging, due to the increasing effect of clustering, resulting in QR films with poorly polarized emission. This study provides insights into the challenges and underlying forces governing the fabrication of composite LC/QR films with homogeneous distribution of QRs and uniform alignment of these emitters, which is important for development of energy-efficient LC displays.