Generalized Susceptibility Theory. IV. The Structure of Electronic Absorption Spectra of Linear Polymers

Abstract

The role of the monomer absorption spectrum in determining the absorption spectrum of a linear polymer is studied in terms of a linear response theory formulation of the complex, frequency-dependent polarizability of the polymer. It is pointed out that a Ketteler-Helmholtz dispersion (combination of positive and negative frequency Lorentzians) is a fundamental form in the theory and, accordingly, model absorption spectra for the monomer, consisting of sets of Ketteler-Helmholtz bands, are used. In each case the polymer spectrum is calculated for various intermolecular coupling strengths. Under the right conditions, all of the intensity from a set of monomer bands appears in a single collective mode of the polymer [cf. A. Herzenberg and A. Modinos, Proc. Phys. Soc. (London) 87, 597 (1966)]. The spectral requirements for such strong coupling and the spectral features of the collective mode are determined. The latter is observed to become a Ketteler-Helmholtz in the strong coupling limit. The contribution of monomer transitions outside the observed frequency range is also considered.