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In this last of three articles on the optical absorption of electrons in a half-filled Peierls-distorted chain we address the dimerized extended Hubbard model in the limit of a large on-site interaction U . When the Hubbard interaction is large both compared to the band width W and the nearest-neighbor interaction V the charge dynamics is properly described by the Harris-Lange model. This model can be exactly mapped onto a model of free spinless Fermions in parallel (Hubbard-)bands of width W which are eventually Peierls-split.To determine the coherent absorption features at low temperatures we design and employ the "no-recoil approximation" in which we assume that the momentum transfer to the spin degrees of freedom can only be ∆q S = 0 or ∆q S = π/a during an optical excitation. We present explicit analytical results for the optical absorption in the presence of a lattice dimerization δ and a nearest-neighbor interaction V for the Néel and dimer state. We find * e-mail: florian@gaston.ill.fr 1 that the coherent part of the optical absorption for V = 0 is given by a single peak at ω = U and broad but weak absorption bands for W δ ≤ |ω − U | ≤ W .The central peak at ω = U only vanishes for δ = 0 in the Néel state. For an appreciable nearest-neighbor interaction V > W/2 almost all spectral weight is transferred to the ∆q C = 0-exciton and the ∆q C = π/a-exciton whose relative spectral weights very sensitively depend on both the lattice and the spin dimerization of the ground state.