Wednesday, October 17, 2012

Superlatives: Kings of Polyene Mountain

(Thanks to BRSM, for unwittingly providing the theme for this post...)

"We can rebuild him...Better, stronger, faster..." - opening to Six Million Dollar Man

Today's society steeps in superlatives. Never content with the ordinary, we want to know who's the richest, fastest, and the best-looking. Our obsession with "most" even extends into our scientific publishing; JACS actively discourages words such as "novel" or "first" from its article titles.

Well, this paper must have slipped into the system unchecked. Behold: longest of the polyenes!
Martinez, Sliwka Org. Lett 2012
(That numbering system means 80 total carbons, and 27 bonds in conjugation. For example, butadiene is C4:2)

Why embark on this synthesis, to chase the olefinic "holy grail?" Three reasons: the pursuit of "lambda ultimate" (how far can we go into the red?), to fix errors in calculated specs (off by 104 nm!), and to create ever-longer molecular wires.

Check out the Supporting Info for an historical polyene primer, from 1899 to the present. Interestingly, the field seems to have run into roadblocks based not just on available synthetic methods, but on the rock-like solubility of many polyaromatics; further frustration stems from the instability of certain cyclic compounds I'm sure would like to Alder all over the place!

My favorite part of this saga? The gorgeous superstructure of the modeled C80:27 polyene.

Martinez, Sliwka Org. Lett 2012

You might expect an all-trans structure to be stiff as a board, but let's think conformationally - each "prenyl" unit has a methyl group bashing up 'A(1,3)-like' against a neighboring hydrogen. To avoid this, it twists and shifts, producing a pleasing undulation in the overall chain.

All kidding aside, the 'longest' title surely won't stand. Now that the authors have improved methods to synthesize soluble, all-trans, long-chain poly-olefins, it's a matter of time before something wild like C220:50 comes out.

Might I suggest "The Longest Polyene...For Now?"

4 comments:

  1. Not to nit pick here. And I know that this is an fantastic synthesis, but polyacetylenes, polythiophenes and polypyrroles are orders of magnitude longer. I know, what with polydispersity, that polymers are not single species, but come on. The shortest strands of a typical polyacetylene sample will be longer than this.

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    Replies
    1. You beat me to this. Amen.

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    2. As someone studying molecular electronics, this news is pretty exciting. You mentioned polydispersity, and the synthesis just reported bypasses that problem. Simulations on monodisperse molecules are therefore much easier to conduct and experiments easier to devise.

      I'm going to have a chat with my advisor about what we should model next ;)

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  2. @Bend

    As someone studying molecular electronics, this news is pretty exciting. You mentioned polydispersity, and the synthesis just reported bypasses that problem. Simulations on monodisperse molecules are therefore much easier to conduct and experiments easier to devise.

    I'm going to have a chat with my advisor about what we should model next ;)

    ReplyDelete