Planar Cyclooctatetraenes and Related Ring Systems: Antiaromaticity and Applications

Antiaromaticity of planar cyclooctatetraene (COT) is high based on magnetic criteria of aromaticity in contrast to its small antiaromatic destabilization. The planar structures of typical COTs are the transition states of the dynamic processes and hence hardly accessible by spectroscopic means. However, some molecules have been designed to have a planar COT core. The planar structure of the COT core potentially causes a narrow HOMO–LUMO (H–L) gap, which is expected to be useful for various applications. In this chapter, the syntheses, antiaromaticity, and optical and electronic applications of planar COTs and related ring systems are reviewed.