Efficient multistep photoinitiated electron transfer in a molecular pentad

Journal Article · Fri Apr 13 00:00:00 EDT 1990 · Science (Washington, D.C.); (USA)

DOI:https://doi.org/10.1126/science.248.4952.199· OSTI ID:6081208

Gust, D; Moore, T A; Moore, A L; Lee, Seung-Joo; Bittersmann, E; Luttrull, D K; Rehms, A A; DeGraziano, J M; Ma, Xiaochun C; Gao, Feng; Belford, R E; Trier, T T ^[1]

---

1. Arizona State Univ., Tempe (USA)

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{sub Zn}) and the other present as the free base (P). The metallated porphyrin bears a carotenoid polyene (C) and the other a diquinone species (Q{sub A}-Q{sub B}). Excitation of the free-base porphyrin in a chloroform solution of the pentad yields an initial charge-separated state, C-P{sub Zn}-P{sup {center dot}+}-Q{sub A}{sup {center dot}{minus}}-Q{sub B}, with a quantum yield of 0.85. Subsequent electron transfer steps lead to a final charge-separated state, C{sup {center dot}+}-P{sub Zn}-P-Q{sub A}-Q{sub B}{sup {center dot}{minus}}, 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{sub A}-Q{sub 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.

• DOE Contract Number: FG02-87ER13791; FG05-87ER75361; FG02-88ER13969
• OSTI ID: 6081208
• Journal Information: Science (Washington, D.C.); (USA), Vol. 248:4952; ISSN 0036-8075
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ELECTRON TRANSFER
ENERGY YIELD
PORPHYRINS
PHOTOCHEMICAL REACTIONS
PHOTOSYNTHESIS
PHOTOSYNTHETIC REACTION CENTERS
CARBOXYLIC ACIDS
CHEMICAL REACTIONS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
SYNTHESIS
YIELDS
400500* - Photochemistry