Abstract A modular approach to azulene building blocks was developed starting from readily available aryl‐substituted cyclopentadiene and ortho‐haloaryl aldehyde by dehydration condensation followed by palladium‐catalyzed C?H coupling. It facilitates the synthesis of four nonalternant isomers of pentacene and hexacene, namely, dibenzoe,gazulene, benzo1,2‐f?:?5,4‐f′diazulene, benzo1,2‐f?:?4,5‐f′diazulene, and naphtho2,3‐f?:?6,7‐f′diazulene, which exhibit narrow band gaps with high stability in addition to protonation‐caused enhanced near‐infrared fluorescence. We discovered that in these isomers, i) constitutional isomerism influences significantly their photoelectric properties and ii) the elongation of the conjugation system does not necessarily lead to a narrowing in the band gap. Due to the easy modifiability of the nonazulene building blocks, this strategy can be extended to modularly prepare numerous multiazulene‐fused aromatics.
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