Azulene - an interesting blue organic compound

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Azulene is a bicyclic organic compound found in certain blue mushrooms and sea creatures, notable for its unique structure resulting from the fusion of cyclopentadiene and cycloheptatriene rings. It features a 10 pi electron system, distinguishing it from compounds like indole. Recent discussions highlight azulene's ability to defy Kasha’s Rule due to its excited-state (anti)aromaticity, which may have implications for solar power technology. Its blue color is unexpected for a conjugated system of this size, challenging conventional assumptions in chemistry. Azulene's intriguing properties have garnered attention in scientific research, indicating its potential for future applications.
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I was reading an article about some interesting features of azulene, a bicyclic organic compound that is apparently present in some blue mushrooms and sea creatures. So, I decided to learn more out of curiosity.

Azulene is usually viewed as resulting from fusion of cyclopentadiene and cycloheptatriene rings. Like naphthalene and cyclodecapentaene, it is a 10 pi electron system.
https://en.wikipedia.org/wiki/Azulene

It is different than indole - https://en.wikipedia.org/wiki/Indole

Excited-State (Anti)Aromaticity Explains Why Azulene Disobeys Kasha’s Rule​

https://pubs.acs.org/doi/10.1021/jacs.3c07625

Knowledge of how the renegade azulene can flout the rules may help scientists harness its energy for solar power tech, according to Popular Mechanics.
. I'm not going to link to the article, since the comment seems overly speculative for now. Suffice it to say that azulene has attracted some attention in the chemistry research area.
 
Chemistry news on Phys.org
Surprising that this is blue. Usually conjugated systems of this size would be yellow/orange. Just goes to show that intuition sometimes leads to spurious conclusions.
 
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