The temperature dependence of spin-selective intramolecular charge recombination (CR) in a series of 2,7-fluorenone (FN1-2) and p-phenylethynylene (PE1-2P) linked donor bridge acceptor molecules with a 3,5-dimethyl-4-(9-anthracenyl) julolidine (DMJ-An) electron donor and a naphthalene-1,8:4,5-bis(dicarboximide) (NI) acceptor was studied using nanosecond transient absorption spectroscopy in the presence of a static magnetic field. Photoexcitation of DMJ-An into its charge transfer band and subsequent electron transfer to NI results in a nearly quantitative yield of (1)(DMJ(+center dot)-An-FNn-NI-center dot) and (1)(DMJ(+center dot)-An-PEnP-NI-center dot), which undergo rapid radical pair intersystem crossing (RP-ISC) to produce the triplet RPs, (3)(DMJ(+center dot)-An-FNn-NI-center dot) and (3)(DMJ(+center dot)-An-PEnP-NI-center dot), respectively. The CR rate constants, kat, in toluene were measured over a temperature range from 270 to 350 K, and a kinetic analysis of k(CR) in the presence of an applied static magnetic field was used to extract the singlet and triplet charge recombination rate constants, k(CRS) and k(CRT), respectively, as well as the intersystem crossing rate constant, k(ST). Plots of In (kT(1/2)) versus 1/T for PE1P show a distinct crossover at 300 K from a temperature-independent singlet CR pathway to a triplet CR pathway that is positively activated with a barrier of 1047 +/- 170 cm(-1). The singlet CR pathway via the FN1 bridge displays a negative activation energy that results from donor bridge and bridge acceptor torsional motions about the single bonds joining them. In contrast, the triplet CR pathway via the FN1-2 and PE1-2P bridges exhibits positive activation energies. The activation barriers to these torsional motions range from 1100 to 4500 cm-1 and can be modeled by semiclassical electron transfer theory.