TY - JOUR
T1 - Temperature dependence of spin-selective charge transfer pathways in donor-bridge-acceptor molecules with oligomeric fluorenone and p -phenylethynylene bridges
AU - Scott, Amy M.
AU - Wasielewski, Michael R
PY - 2011/3/9
Y1 - 2011/3/9
N2 - 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+•-An-FNn-NI-•) and 1(DMJ+•-An-PEnP-NI-•), which undergo rapid radical pair intersystem crossing (RP-ISC) to produce the triplet RPs, 3(DMJ+•-An-FNn-NI -•) and 3(DMJ+•-An-PE nP-NI-•), respectively. The CR rate constants, k CR, in toluene were measured over a temperature range from 270 to 350 K, and a kinetic analysis of kCR in the presence of an applied static magnetic field was used to extract the singlet and triplet charge recombination rate constants, kCRS and kCRT, respectively, as well as the intersystem crossing rate constant, kST. Plots of ln (kT1/2) 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.
AB - 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+•-An-FNn-NI-•) and 1(DMJ+•-An-PEnP-NI-•), which undergo rapid radical pair intersystem crossing (RP-ISC) to produce the triplet RPs, 3(DMJ+•-An-FNn-NI -•) and 3(DMJ+•-An-PE nP-NI-•), respectively. The CR rate constants, k CR, in toluene were measured over a temperature range from 270 to 350 K, and a kinetic analysis of kCR in the presence of an applied static magnetic field was used to extract the singlet and triplet charge recombination rate constants, kCRS and kCRT, respectively, as well as the intersystem crossing rate constant, kST. Plots of ln (kT1/2) 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.
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U2 - 10.1021/ja1095649
DO - 10.1021/ja1095649
M3 - Article
C2 - 21319798
AN - SCOPUS:79952253877
VL - 133
SP - 3005
EP - 3013
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 9
ER -