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Amorphous Organic LED's . Light-emitting diodes (LEDs) are the basis for many useful products including the screens on laptops computers and digital watches. Injecting electrons and holes into a compound allows for electrons and holes to combine. As the electron moves to its ground state, a photon of light is emitted (fig. 1). An ideal LED emits an equal amount of photons for every electron injected into the device. 
All LEDs that are currently in use are fabricated from inorganic compounds. We are attempting to synthesize an organic compound to be fabricated as an LED due to the advantages that they have over inorganic based LEDs. Firstly, they can be easily spin-caste into thin films, which offers a huge advantage over inorganic compounds. The compound can actually be spun-cast directly onto the substrate of the device (fig. 2). This allows for inexpensive an easy processing. Organic polymers are flexible. This allows for compounds that can be directly spun-cast onto a flexible plastic sheet that can then be illuminated. Another advantage is that these organic compound based devices can be fabricated by delivering the organic layer with an inkjet printer allowing for ultra high resolution and superior patterning. Finally, organic based LEDs have a much higher photoluminescence and quantum yield than inorganic based LEDs, potentially leading to a brighter more efficient device. Organic based LED devices do have some disadvantages, however. They are generally less stable. Each device must either be encapsulated to keep it from breaking down from contact with oxygen, or some other means of preservation to keep it operating properly. Small organic molecules tend to be crystalline, which reduces emission yields. The current research is geared towards working around these disadvantages, further encouraging the synthesis of the target compound -- tetrahedral fluorene. The target compound is a relatively small molecule rather than a polymer. The advantage of synthesizing a small molecule instead of a polymer is that the molecular weight of the compound will be known. The exact structure of the compound will be known, unlike the case with polymers, where they can vary in size, and the exact structure is impossible to know. The Bazan group previously discovered that conjugated molecules with tetrahedral geometry are resistant to crystallization, thus solving the problem that small molecules tend to be crystalline. By arranging the target compound in tetrahedral geometry, the Bazan groups' discovery will be used in the synthesis of the compound to optimize its LED characteristics. Return to the RISE 2000 project list |
