Nanocrystal/J-aggregate constructs : chemistry, energy transfer, and applications
Author(s)Walker, Brian J. (Brian Jacob)
Massachusetts Institute of Technology. Dept. of Chemistry.
Moungi G. Bawendi.
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The interaction of light with matter is one of the most central subjects to modern chemistry. Two types of materials, semiconductor nanocrystals and J-aggregates of cyanine dyes, have been developed chiefly due to their potential for interacting with light in interesting and productive ways. At the same time, existing spectroscopy and microscopy tools enable the study of these photonic materials, their dynamics, and their interactions. Although semiconductor nanocrystals and J-aggregates have complementary physical properties, the coupling between them requires new methods to control the interface between the organic (J-aggregate) and inorganic (nanocrystal) material. This thesis is about the interfacial chemistry, photophysical characterization, and selected applications of J-aggregated cyanine dyes conjugated with semiconductor nanocrystals. Chapter 1 begins with a brief review of J-aggregates and semiconductor nanocrystals together with referrals to other scources and motivation for the present work. Because the electronic excited states of both J-aggregates and semiconductor nanocrystals are characterized by a bound electron-hole pair, they can be grouped under the class of excitonic materials, and the coupling of J-aggregates with excitonic inorganic materials is reviewed. To control J-aggregate/nanocrystal interactions, it is important to preserve the aggregate structure while achieving favorable energy transfer. This challenge is the subject of Chapters 2 and 3, in which new ligand chemistry was developed to achieve near-unity energy transfer efficiency from the J-aggregates to the nanocrystal quantum dots in solution (Ch. 2) and in a solid state thin film (Ch. 3). These hybrid J-aggregate/nanocrystal constructs result in emission enhancement through energy transfer across the organic/inorganic interface, with the strongly-coupled J-aggregates serving as optical antennae to the nanocrystals. In the process, it was discovered that the ligand directs formation of J-aggregates onto the nanocrystal surface. In Chapter 4, the template-directing ligand is used on semiconductor nanowires grown from solution to realize a new photodetector design. Here, the excitation energy transfers from J-aggregated dyes to the nanowires, enhancing the photocurrent of the device and creating an artificial solid-state photodetector whose self assembly and aggregated antenna molecules are analogous to a photosynthetic light harvesting complex. Additionally, the nanowire/J-aggregate self-assembly generalizes to J-aggregates of three different color dyes (red/green/blue), providing a wavelength selectivity absent in biological light harvesting. In Chapter 5, the kinetics of indium phosphide (InP) semiconductor nanocrystal synthesis is discussed. InP is benficial for nanocrystal applications in biology or display technologies, as it does not contain lead or cadmium. However, the molecular mechanism of InP nanocrystal synthesis had been essentially unexplored. By studying the reaction kinetics of InP synthesis, a mechanism is proposed for InP. As in the case of the chemistry described in Chapters 2-4, it is clear that non-covalent interactions are vital to achieving control during nanocrystal synthesis.
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2011.Vita. Cataloged from PDF version of thesis.Includes bibliographical references (p. 119-128).
DepartmentMassachusetts Institute of Technology. Dept. of Chemistry.
Massachusetts Institute of Technology