title: Efficient multistep photoinitiated electron transfer in a molecular pentad.
abstract: A synthetic five-part molecular device has been prepared that uses a multistep electron transfer strategy similar to that of photosynthetic organisms to capture light energy and convert it to chemical potential in the form of long-lived charge separation. It consists of two covalently linked porphyrin moieties, one containing a zinc ion (P(Zn)) and the other present as the free base (P). The metailated porphyrin bears a carotenoid polyene (C) and the other a diquinone species (Q(A)-Q(B)). Excitation of the free-base porphyrin in a chloroform solution of the pentad yields an initial charge-separated state, C-P(Zn)-P(.+).-Q(A)(-)-Q(B), with a quantum yield of 0.85. Subsequent electron transfer steps lead to a final charge-separated state, C(.+)-P(Zn)-P-Q(A)-Q(B)(.-), which is formed with an overall quantum yield of 0.83 and has a lifetime of 55 microseconds. Irradiation of the free-base form of the pentad, C-P-P-Q(A)-Q(B), gives a similar charge-separated state with a lower quantum yield (0.15 in dichloromethane), although the lifetime is increased to approximately 340 microseconds. The artificial photosynthetic system preserves a significant fraction ( approximately 1.0 electron volt) of the initial excitation energy (1.9 electron volts) in the long-lived, charge-separated state.
authors.forename: D
authors.initials: D
authors.lastname: Gust
authors.forename: T A
authors.initials: TA
authors.lastname: Moore
authors.forename: A L
authors.initials: AL
authors.lastname: Moore
authors.forename: S J
authors.initials: SJ
authors.lastname: Lee
authors.forename: E
authors.initials: E
authors.lastname: Bittersmann
authors.forename: D K
authors.initials: DK
authors.lastname: Luttrull
authors.forename: A A
authors.initials: AA
authors.lastname: Rehms
authors.forename: J M
authors.initials: JM
authors.lastname: Degraziano
authors.forename: X C
authors.initials: XC
authors.lastname: Ma
authors.forename: F
authors.initials: F
authors.lastname: Gao
authors.forename: R E
authors.initials: RE
authors.lastname: Belford
authors.forename: T T
authors.initials: TT
authors.lastname: Trier