Delocalization and Migration of Excitation Energy and Charge in Supramolecular Systems

Fujitsuka, Mamoru; Majima, Tetsuro

doi:10.1002/9781118095300.ch12

Cited by 1 publication

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“…Spatially directed energy transfer following light absorption is at the heart of the light-harvesting antenna of photosynthesis. − Transporting energy over significant distances at rapid rates is dependent both on driving force and optimal placement of chromophores. A variety of strategies have been explored to model and mimic the photosynthetic antenna behavior, for example, based on spatially ordered arrays in dendrimers, polymers, MOFs, and peptides. − Of these, peptides prepared by stepwise site-by-site synthesis are appealing in offering synthetic control both in composition and in relative positioning of light-absorbing units due to the modular, stepwise approach offered by the solid-phase peptide synthetic technique.…”

Section: Introductionmentioning

confidence: 99%

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Distance Dependence of Intrahelix Ru^II* to Os^II Polypyridyl Excited-State Energy Transfer in Oligoproline Assemblies

et al. 2013

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Energy transfer between the metal-to-ligand charge transfer (MLCT) excited states of [Pra [M(II)(bpy)2(4-Me-4'(-N(H)CO)bpy)](PF6)2 units ([Pra(M(II)bpy2(mbpy)](2+): M(II) = Ru(II) or Os(II), bpy = 2,2'-bipyridine, mbpy = 4'-methyl-2,2'-bipyridine-4-carboxamido, Pra = 4-M(II)-L-proline) linked covalently to oligoproline assemblies in room temperature acetonitrile occurs on the picosecond-nanosecond time scale and has been time-resolved by transient emission measurements. Three derivatized oligoprolines, [CH3-CO-Pro6-Pra[Os(II)(bpy)2(mbpy)](2+)-Pro2-Pra[Ru(II)(bpy)2(mbpy)](2+)-Pro2-Pra[Ru(II)(bpy)2(mbpy)](2+)-Pro6-Glu-NH2](6+) (ORR-2, Pro = L-proline and Glu = glutamic acid); [CH3-CO-Pro6-Pra[Os(II)(bpy)2(mbpy)](2+)-Pro3-Pra[Ru(II)(bpy)2(mbpy)](2+)-Pro3-Pra[Ru(II)(bpy)2(mbpy)](2+)-Pro6-Glu-NH2](6+) (ORR-3); and CH3-CO-Pro6-Pra[Os(II)(bpy)2(mbpy)](2+)-Pro5-Pra[Ru(II)(bpy)2(mbpy)](2+)-Pro5-Pra[Ru(II)(bpy)2(mbpy)](2+)Pro6-Glu2-NH2](6+) (ORR-5), were prepared by using solid-phase peptide synthesis. Given the helical nature of the resulting assemblies and the nature of the synthesis, composition, length, and loading pattern are precisely controlled in the assemblies. In acetonitrile, they adopt a proline I helical secondary structure, confirmed by circular dichroism, in which the appended chromophores are ordered in well-defined orientations and internuclear separation distances although helix formation for ORR-2 is incomplete. Quantitative comparison of oligoproline ground-state absorption and steady-state emission spectra to those for the constituents, [Boc-Pra[M(II)(bpy)2(mbpy)](2+)-OH](PF6)2 (Boc = N(α)-(1,1-dimethylethoxycarbonyl), shows that following Ru(II) light absorption, Ru(II)* undergoes facile energy transfer resulting in sensitization of Os(II). Sensitization efficiencies are 93% for ORR-2, 77% for ORR-3, and 73% for ORR-5. Picosecond-resolved emission measurements reveal complex, coupled dynamics that arise from excited-state decay and kinetically competitive -Ru(II)*-Ru(II)- → -Ru(II)-Ru(II)*- energy transfer migration/exchange and downhill -Ru(II)*-Os(II) → -Ru(II)-Os(II)* energy transfer. These processes were modeled simultaneously to extract rate constants for Ru(II)* → Ru(II) energy-transfer migration, k(Ru*-Ru), and Ru(II)* → Os(II) energy transfer, k(Ru*-Os). For ORR-2, k(Ru*-Ru) = 2.9 × 10(7) s(-1) and k(Ru*-Os) = 3.4 × 10(8) s(-1). For ORR-3, k(Ru*-Ru) = 1.2 × 10(7) s(-1) and k(Ru*-Os) = 1.3 × 10(8) s(-1). For ORR-5, k(Ru*-Ru) = 3.6 × 10(6) s(-1) and k(Ru*-Os) = 5.8 × 10(7) s(-1), all in acetonitrile at 22 °C. The data were analyzed by assuming Dexter energy transfer with the Franck-Condon factors arising from intramolecular structural and medium changes evaluated by use of an emission spectral fitting procedure. Fits of the data to the Dexter mechanism were consistent with the predicted distance dependence of energy transfer.

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Section: Introductionmentioning

confidence: 99%

“…H NMR spectra were recorded on a 200 MHz AC200 Bruker spectrometer. 13 C NMR spectra were obtained on a 400 MHz Varian XL 400 spectrometer. Thin layer chromatography was performed on Bakerflex alumina plates.…”

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confidence: 99%

Distance Dependence of Intrahelix Ru^II* to Os^II Polypyridyl Excited-State Energy Transfer in Oligoproline Assemblies

et al. 2013

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Delocalization and Migration of Excitation Energy and Charge in Supramolecular Systems

Cited by 1 publication

References 90 publications

Distance Dependence of Intrahelix Ru^II* to Os^II Polypyridyl Excited-State Energy Transfer in Oligoproline Assemblies

Distance Dependence of Intrahelix Ru^II* to Os^II Polypyridyl Excited-State Energy Transfer in Oligoproline Assemblies

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Delocalization and Migration of Excitation Energy and Charge in Supramolecular Systems

Cited by 1 publication

References 90 publications

Distance Dependence of Intrahelix RuII* to OsII Polypyridyl Excited-State Energy Transfer in Oligoproline Assemblies

Distance Dependence of Intrahelix RuII* to OsII Polypyridyl Excited-State Energy Transfer in Oligoproline Assemblies

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Distance Dependence of Intrahelix Ru^II* to Os^II Polypyridyl Excited-State Energy Transfer in Oligoproline Assemblies

Distance Dependence of Intrahelix Ru^II* to Os^II Polypyridyl Excited-State Energy Transfer in Oligoproline Assemblies