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Topic: Resources that explain conjugated systems and HOMO/LUMO gap  (Read 1166 times)

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Offline Meter

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Hello.

I need some good sources that explain why the HOMO/LUMO gap tends to decrease when the scope of a conjugated system increases. Preferably also something which uses other examples than ethene/butadiene. It needs to be something I can cite as a source for an oral presentation.

Any help?

Thanks.
« Last Edit: June 12, 2021, 02:22:17 PM by Meter »

Offline Babcock_Hall

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Re: Resources that explain conjugated systems and HOMO/LUMO gap
« Reply #1 on: June 12, 2021, 02:57:10 PM »
Would an introductory quantum chemistry textbook have something?  I am thinking along the lines of a particle-in-a-box treatment.

Carotenoids typically have between 9 and 13 conjugated bonds.  There are some complications that affect the wavelength, such as the geometry of the double bond and substituents.

Offline Meter

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Re: Resources that explain conjugated systems and HOMO/LUMO gap
« Reply #2 on: June 12, 2021, 03:04:31 PM »
Would an introductory quantum chemistry textbook have something?  I am thinking along the lines of a particle-in-a-box treatment.

Carotenoids typically have between 9 and 13 conjugated bonds.  There are some complications that affect the wavelength, such as the geometry of the double bond and substituents.
It's hard to say, as I don't own a quantum chemistry textbook yet. What I really would like is an online source, like a .pdf article or similar. I found a good explanation on stackexchange, but if I'm asked for a source, I really don't wanna say "some stranger who got a lot of upvotes".

Offline Corribus

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Re: Resources that explain conjugated systems and HOMO/LUMO gap
« Reply #3 on: June 16, 2021, 03:59:21 PM »
It's a bit of a strange thing to ask a reference for. There are a lot of simple quantum models that show the bandgap decreases; none of them is "the reason". Most of them reproduce the broad observation, but fail pretty spectacularly in important details. A physical chemistry or even general chemistry textbook would probably be your best bet because the particle in the box model is often crudely applied to conjugated polyenes in these courses.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

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