Subject: polyene spectra

From: Ulrike Salzner <[email-masked]>
Date: Fri, 01 Nov 2002 09:38:32 +0200

Hello,
in the literature it is commonly stated that UV absorbtion energies of 
polyenes with increasing chain lengths decrease approximately linearly 
when plotted against 1/n, the number of repeat units. Does anyone know 
where this has been stated for the first time and at which level of 
theory this is true exactly. I am writing a paper and I want to give a 
proper reference, however, usually people do not give a citation or they 
just cite their own previous papers. I suspect that the relationship 
does not necessarily hold when higher levels of theory are used and when 
the geometries are optimized. Can somebody comment on this?
Thanks in advance,
Ulrike Salzner

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From: "William F. Polik" <[email-masked]>
Date: Fri, 01 Nov 2002 10:04:28 -0500

Ulrike,

This is a very common physical chemistry experiment illustrating the 
Particle-in-a-Box that is described in most physical chemistry laboratory 
textbooks, as well as in several articles in the Journal of Chemical 
education over the last decade.

You can find several references to the older literature in Chapter 11 of 
Jaffe & Orchin, "Theory and Applications of UV Spectroscopy".  One article 
in particular that derives this result is
   H. Kuhn, Journal of Chemical Physics, vol 17, p. 1198 (1949)

At 02:38 AM 11/1/02, you wrote:
>where this has been stated for the first time and at which level of theory 
>this is true exactly. I am writing a paper and I want to give a proper 
>reference, however, usually people do not give a citation or they just 
>cite their own previous papers. I suspect that the relationship does not 
>necessarily hold when higher levels of theory are used and when the 
>geometries are optimized. Can somebody comment on this?

Will Polik

---

From: Brent Krueger <[email-masked]>
Date: Fri, 01 Nov 2002 12:36:38 -0500

Ulrike,

This is indeed a complicated problem.  The earlier work that Will mentions 
does verify the energy to 1/n relationship.  Note, however, that the 
transition observed in polyenes is generally S2 <--> S0 and I think that 
wasn't really understood at the time.

I believe real progress in understanding the nature of polyene electronic 
states (S0, S1, and S2) began in the early 70s.  See for instance:
    Hudson, B. S.; Kohler, B. E. Chem. Phys. Lett. 1972, 14, 299-304.
    Schulten, K.; Karplus, M. Chem. Phys. Lett. 1972, 15, 305-309.

A handy reference that reviews most of this "neo-early" work is:
    Hudson, B. S.; Kohler, B. E.; Schulten, K. In Excited States; Lim, E. 
C., Ed.; Academic Press: New York, 1982; Vol. 6, pp 1-95.

I must admit that I am not too up on current polyene work, but you should 
look up recent papers from Hsu and Head-Gordon and from the Robb group.

Cheers,
Brent

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____________________________________________
Brent P. Krueger

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