The photoexcitation processes of two donoracceptor-type copolymers PCFBT with different ratios between the donor and the acceptor (PCFBT0.5 and PCFBT0.1) in the solution system are systematically studied. If the number of the donor is equal to that of the acceptor in one repeat unit (such as PCFBT0.5), intrachain charge transfer (ICT) can occur and participate in the relaxation of the excited state after photoexcitation. When the number of donors is much larger than that of acceptors (such as PCFBT0.1) in one repeat unit, the ICT character can disappear, and the localized exciton decay process is dominant in the relaxation of the copolymer, which also involves an excitation intensity-independent vibrational thermal relaxation process at the initial time. The results further the understanding of the basic structure-property relationship. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 992-996