Polyazaacene and Cyclazaacene Precursors Synthesized by Dehydration Condensation from a Versatile Bis‐
α
‐diketone Unit Having an Anthracene Skeleton (Polyazaacene and Cyclazaacene Precursors Synthesized by Dehydration Condensation from a Versatile Bis‐ α ‐diketone Unit Having an Anthracene Skeleton)