Synthesis, Spectroscopy, and Morphology of Tetrastilbenoidmethanes.
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Low band gap molecular and polymeric organic materials are currently being considered for the active component in a variety of optoelectronic devices, most notably as the emissive layer in light-emitting diodes. 1 It is generally believed that the morphology adopted by these materials plays a fundamental role in defining their bulk performance. For example, completely amorphous and ultrapure thin films appear to provide the longest device lifetimes, combined with the highest efficiency and emissive brightness. 2 While sufficiently pure films of low molecular weight fluorescent compounds can be obtained by sublimation under high vacuum, these tend to recrystallize over time, thus precipitating device failure. 3 Luminescent polymeric materials can be designed to remain amorphous, even at elevated temperatures, but they are more difficult to obtain in high purity. 4,5 Furthermore, the close association of polymer chains in the solid state can lead to crystalline domains. 6 Ordered polymer regions appear to reduce emission efficiency by promoting low-energy nonor weakly emissive excimer or aggregate states. 7 Ultimately, because of facile energy migration, these low-energy sites can dominate the optical properties, even when present in small concentration. 8