Azulene is a pretty neat substance. As the name suggests, it displays a peculiar blue color. First synthesized in the 1930s, azulene has been used in medicine for its bioactive properties. Now azulene derivatives are being studied for use in organic electronics such as n-type semiconductors, solar cells and non-linear optics. This is made possible by the functionalization of the azulene ring. Odd-positions of the ring had been researched extensively for their high reactivity, though it was hard to select their functionality due to their electronic properties. Highly functionalized azulenes were enabled by cross-coupling reactions of even-numbered positions of azulenes. However, it has been difficult to synthesize these precursors.
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Source: Phys.org