[Meter]

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.

[Babcock_Hall]

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.

[Meter]

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".

[Corribus]

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.