Comparison of the chemical structure of a conventional "linear" perylene bisimide with that of the new Z-shaped perylene bisimide.
There has been a considerable interest in the development of highly conjugated organic materials for use in molecular sensors and electronics, flat panel displays, solid-state lighting, and lightweight photovoltaics. Perylenes (see the preceding figure), primarily perylene bisimides, are one class of conjugated organics that has received particular attention for these applications. These compounds absorb and emit in the visible region of the spectrum and have large photoluminescence and electroluminescence efficiencies, making them well suited for many of the applications mentioned. All perylene bisimides reported to date have been linear systems prepared by conventional imidization chemistry.
In fiscal year 2005, researchers from the NASA Glenn Research Center and the Ohio Aerospace Institute (OAI) developed a new synthetic approach that enables the preparation of a novel class of Z-shaped perylene bisimides (see the preceding figure). This new approach offers greater flexibility in the types of perylene bisimides that can be prepared and enables the “tuning” of the electronic and optical properties of these molecules by the placement of appropriate groups on the sides and ends of the perylene. In addition, these bisimides can be readily incorporated into polymers both at the imide rings and on the pendant groups.
Like conventional linear perylene bisimides, these new Z-shaped systems have absorption in the visible region of the spectrum and exhibit intense fluorescence. An example of the absorption and emission spectra of one of these dyes is shown in the following figure. In solution and doped into a polystyrene film, this dye exhibits a bright lime-green fluorescence (see the inset). Unlike conventional perylene bisimides, a pure solid sample of this new bisimide has a reddish-orange fluorescence. This change in color is due to the formation of excited-state complexes in which the perylene molecules stack one on top of the other. It should be possible to exploit this behavior in the development of “molecular strain gauges” by incorporating these perylene stacks into a polymer film that could change color from orange to green when stretched.
Absorption and emission spectra of Z-shaped perylyene bisimide in dichloromethane. The inset shows fluorescence emission from the bisimide in a pure microcrystalline sample (left), in a polystyrene film (center), and in dichloromethane solution (right) excited with a hand-held, broadband ultraviolet source.
Long description of figure 2.
These materials are under further development for use in electroluminescent polymers for solid-state lighting and displays for spacecraft and aircraft, fluorescent dyes for chemical sensors, and electrically conductive polymers for use in molecular electronic devices.
Find out more about the research of Glenn’s Polymers Branch: http://www.grc.nasa.gov/WWW/5000/MaterialsStructures/polymers/
Glenn contact:
Dr. Michael A. Meador, 216-433-9518, Michael.A.Meador@nasa.gov
Ohio Aerospace Institute (OAI) contacts:
Dr. Daniel S. Tyson, 216-433-3188, Daniel.S.Tyson@nasa.gov; and Dr. Faysal Ilhan, 216-433-6094, Ulvi.F.Ilhan@nasa.gov
Authors:
Dr. Michael A. Meador, Dr. Daniel S. Tyson, and Dr. Faysal Ilhan
Headquarters program office:
Aeronautics Research
Programs/Projects:
Vehicle Systems, Exploration Systems
Last updated: October 16, 2006
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