Tuning Quantum-Dot Organization in Liquid Crystals for Robust Photonic Applications

• Published in: Chemphyschem Vol. 15; no. 7; pp. 1413 - 1421
• Main Authors: Rodarte, Andrea L., Nuno, Zachary S., Cao, Blessing H., Pandolfi, Ronald J., Quint, Makiko T., Ghosh, Sayantani, Hein, Jason E., Hirst, Linda S.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 19.05.2014; WILEY‐VCH Verlag; Wiley; Wiley Subscription Services, Inc
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Fluorescence; ligand exchange; Ligands; Liquid crystals; Materials science; Nanoscale materials and structures: fabrication and characterization; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Other topics in nanoscale materials and structures; Photoluminescence; Physics; Quantum dots; Structure of solids and liquids; crystallography; Quantum dots; Photoluminescence; Fluorescence; Ligands; ligand exchange; Liquid crystals; Nanostructured materials; quantum dots; photoluminescence; liquid crystals; fluorescence
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.201301007

Mesogenic ligands have the potential to provide control over the dispersion and stabilization of nanoparticles in liquid crystal (LC) phases. The creation of such hybrid materials is an important goal for the creation of soft tunable photonic devices, such as the LC laser. Herein, we present a comparison of isotropic and mesogenic ligands attached to the surface of CdSe (core‐only) and CdSe/ZnS (core/shell) quantum dots (QDs). The mesogenic ligand′s flexible arm structure enhances ligand alignment, with the local LC director promoting QD dispersion in the isotropic and nematic phases. To characterize QD dispersion on different length scales, we apply fluorescence microscopy, X‐ray scattering, and scanning confocal photoluminescent imaging. These combined techniques demonstrate that the LC‐modified QDs do not aggregate into the dense clusters observed for dots with simple isotropic ligands when dispersed in liquid crystal, but loosely associate in a fluid‐like droplet with an average interparticle spacing >10 nm. Embedding the QDs in a cholesteric cavity, we observe comparable coupling effects to those reported for more closely packed isotropic ligands. Dots with liquid‐crystalline ligands are synthesized and dispersed in the nematic and cholesteric phases at different concentrations. Fluorescence microscopy, scanning confocal photoluminescence microscopy, and X‐ray diffraction reveal details of the quantum‐dot (QD) cluster packing. Spectroscopic measurements demonstrate the applicability of the QDs for photonic applications.