Circular Dichroism of a Finite Number of Identical Chromophores in a Helical Arrangement

Compact expressions to calculate the transition energies, absorption line strengths, and rotational line strengths of circular dichroism for the excitonic states in a helical arrangement of N identical chromophores are presented. The absorption spectrum A(n) and the CD spectrum C(nu) are given in terms of the same function G(nu, alpha) as A(nu) = sigma(1) G(nu, 0) +alpha(2)G(nu, alpha), C(nu) = (s(1) - s(2))G(nu, alpha) + s(2)G(nu, alpha), + S(B)d/d nu G(nu, alpha). The function G(nu, a) depends only on the helical angle a and the number N of interacting chromophores. An analytical expression can be given when only next-neighbor interactions are considered. All other structural parameters of the system (e. g. orientation of transition dipoles and the translation vector of the helix) enter only into the prefactors a(j) and s(j).