The dynamics and efficiencies of photoinduced charge separation across alternating AT, ATA, ATAT, and ATATA base pair sequences in synthetic DNA hairpins have been determined by means of femtosecond time-resolved transient absorption spectroscopy. When compared to our results for charge transport across poly(A) sequences, both the rate constants and efficiencies are lower for the poly (AT) sequences, especially at short distances (3 or 4 base pairs). At longer distances, charge separation becomes weakly distance-dependent for poly(AT) as well as poly(A) sequences. Both the poly(AT) and poly(A) sequences undergo charge separation via a multistep mechanism consisting of photochemical hole injection into the neighboring A followed by hole transport and hole trapping.