Azulene - an interesting blue organic compound

[Astronuc]

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.

 

[Mayhem]

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.