Photoinduced electron transfer in photorobust coumarins linked with electron donors affording long lifetimes of triplet charge-separated states

Motonobu Murakami, Kei Ohkubo, Takashi Nanjo, Kazunori Souma, Nobuo Suzuki, Shunichi Fukuzumi

Research output: Contribution to journalArticlepeer-review

50 Scopus citations

Abstract

Electron donor (D) substituted 3-ethoxycarbonylcoumarin (CM) derivatives [D-CM: D=4-diphenylaminophenyl (DPA), 4-diethylaminophenyl (DEA), 4-dimethylaminophenyl (DMA), and 2- methyl-4-dimethylaminophenyl (MeDMA)] are synthesized and characterized. Photoinduced electron transfer (ET) from the D moiety to the acceptor (CM) and back electron transfer (BET) are investigated by femtosecond and nanosecond laser flash photolysis measurements. Femtosecond laser excitation at 355 nm of a deaerated acetonitrile (MeCN) solution of D-CM shows generation of the singlet charge-separated (CS) state [1(D+-CM-)] by ET from D to the singlet excited state of the CM moiety (1CM*), and this is followed by rapid decay within 3 ns to afford the triplet excited state (D-3CM*). Nanosecond laser excitation of a deaerated MeCN solution of D-CM results in formation of the triplet CS state by ET from D to 3CM*. The quantum yield of formation of the triplet CS state [3(DPA+-CM-)] in the presence of iodobenzene (PhI) in deaerated MeCN increases with increasing concentration of PhI to reach 27% at 0.5m PhI. The triplet CS state decays by bimolecular BET because of the long CS lifetime by unimolecular BET. Formation of the long-lived triplet CS state was confirmed by electron spin resonance (ESR) measurements. The photorobust nature of DPA-CM is demonstrated by multiple laser pulse excitation (>1000 times) at 355 nm. The photoinduced ET and BET rate constants of a series of D-CM are thoroughly analyzed in light of the Marcus theory of electron transfer.

Original languageEnglish
Pages (from-to)2594-2605
Number of pages12
JournalChemPhysChem
Volume11
Issue number12
DOIs
StatePublished - 2010

Keywords

  • Donor-acceptor systems
  • Dyes/pigments
  • Electron transfer
  • Laser flash photolysis
  • Photochemistry

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