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TDDFT calculations are associated to an extrapolation scheme to predict the optical properties of twelve donor-acceptor copolymers, in which carbazole, benzodithiophene or cyclopentadithiophene donor subunits are combined to benzofurazane, benzothiadiazole or diketopyrrolopyrrole acceptor moieties. Relative excitation energies and absorption strengths are rationalized in terms of geometrical, electronic and optical descriptors. It is shown that the combination of a cyclopentadithiophene with a diketopyrrolopyrrole leads to the lowest excitation energy and highest light absorption efficiency within the series. However, combining cyclopentadithiophene and benzodithiophene subunits appears as more efficient for solar cell applications due to better energy level alignment with respect to PCBM. [ABSTRACT FROM AUTHOR]