A non-perturbation method for the optical properties of helical polymers

✍ Scribed by F. M. Loxsom; L. Tterlikkis; William Rhodes

• Publisher: Wiley (John Wiley & Sons)
• Year: 1971
• Tongue: English
• Weight: 801 KB
• Volume: 10
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.360101205

✦ Synopsis

The optical absorpt,ion and circular dichroisin (CD) of poly-1.-alariine in an a-helical conformation are computed in terms of monomer properties by use of Bogolirtbov exciton theory (a noii-pert.rirbation method). It was shown earlier that a proper formulation of the theory of CI> for large molecular systems permits the use of periodic boundary conditions, a feature which greatly simplifies calculat,ions as well as conceptual urtderstandiiig.

It is found that the shape of the observed CII spectrum can be explained in terms of the two rotational strength components and an electric dipole strength component referred to as the helix term. Comparisons of the results of perturbation theory and Bogoliubov exciton theory show that pert,urbation theory is valid for absorption but, is inadequate for CL) if the coupling among monomers is sufficiently large to predict t.he observed hypochromism.

* I n the linear response theory method the empirical frequencydependent monomer polarizability is used; whereas in the Bogoliubov exciton method monomer transitions a t definite frequencies are used.