Light-Induced Electron Transfer in Pyropheophytin−Anthraquinone and Phytochlorin−Anthraquinone Dyads:  Influence of Conformational Exchange

Tkachenko, Nikolai V.; Tauber, Andrei Y.; Grandell, D.; Hynninen, Paavo H.; Lemmetyinen, Helge

doi:10.1021/jp983765q

Cited by 28 publications

(21 citation statements)

References 27 publications

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“…23; for representative chlorin dyads and multads prepared more recently, see Refs. 24–45). Extensive work has also been devoted to the preparation and study of self‐assembling chlorins (46).…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Excited‐state Photodynamics of a Chlorin–Bacteriochlorin Dyad—Through‐space Versus Through‐bond Energy Transfer in Tetrapyrrole Arrays

Muthiah

Kee

Diers

et al. 2008

Photochem & Photobiology

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Understanding energy transfer among hydroporphyrins is of fundamental interest and essential for a wide variety of photochemical applications. Toward this goal, a synthetic free base ethynylphenylchlorin has been coupled with a synthetic free base bromobacteriochlorin to give a phenylethyne-linked chlorin-bacteriochlorin dyad (FbC-pe-FbB). The chlorin and bacteriochlorin are each stable toward adventitious oxidation because of the presence of a geminal dimethyl group in each reduced pyrrole ring. A combination of static and transient optical spectroscopic studies indicate that excitation into the Qy band of the chlorin constituent (675 nm) of FbC-pe-FbB in toluene results in rapid energy transfer to the bacteriochlorin constituent with a rate of approximately (5 ps)(-1) and efficiency of >99%. The excited bacteriochlorin resulting from the energy-transfer process in FbC-pe-FbB has essentially the same fluorescence characteristics as an isolated monomeric reference compound, namely a narrow (12 nm fwhm) fluorescence emission band at 760 nm and a long-lived (5.4 ns) Qy excited state that exhibits a significant fluorescence quantum yield (Phif=0.19). Förster calculations are consistent with energy transfer in FbC-pe-FbB occurring predominantly by a through-space mechanism. The energy-transfer characteristics of FbC-pe-FbB are compared with those previously obtained for analogous phenylethyne-linked dyads consisting of two porphyrins or two oxochlorins. The comparisons among the sets of dyads are facilitated by density functional theory calculations that elucidate the molecular-orbital characteristics of the energy donor and acceptor constituents. The electron-density distributions in the frontier molecular orbitals provide insights into the through-bond electronic interactions that can also contribute to the energy-transfer process in the different types of dyads.

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Section: Introductionmentioning

confidence: 99%

Synthesis and Excited‐state Photodynamics of a Chlorin–Bacteriochlorin Dyad—Through‐space Versus Through‐bond Energy Transfer in Tetrapyrrole Arrays

Muthiah

Kee

Diers

et al. 2008

Photochem & Photobiology

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“…[11] ), using a theory that has become popular under the name of one of the chief proponents, R. Marcus. Many focus on the effects of the driving force (∆G) on k ET (see for example ref.…”

Section: Introductionmentioning

confidence: 99%

The Role of the Electronic Structure of the Porphyrin as Viewed by EPR/ENDOR Methods in the Efficiency of Biomimetic Model Compounds for Photosynthesis

Huber

2001

Eur. J. Org. Chem.

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A project to investigate the parameters that determine the efficiency of biomimetic porphyrin quinone model compounds for photosynthesis is described. It should aid in understanding the origin of the high efficiency of energy conversion in the light‐induced charge separation in photosynthesis. Specifically, the contribution of the electronic matrix element to the electron transfer (ET) rates is addressed. Targeting the electronic structure of the ET components, EPR (electron paramagnetic resonance) and ENDOR (electron nuclear double resonance) spectroscopy were performed on the appropriate radical derivatives of the porphyrins and quinones to determine MO coefficients. Together with semiempirical MO methods, these coefficients were used to obtain information on the frontier orbitals of the donor and acceptor moieties, the porphyrins, and quinones of the model compounds. The porphyrin frontier orbitals (HOMO and LUMO) have been implicated in the balance of ET rates for charge separation and charge recombination, which is related to the efficiency. A model is presented to correlate the substitution pattern of the porphyrin with the efficiency of the model compound. In particular, the effect of porphyrin substitution, including the covalent link to an acceptor, and the comparison of porphyrins with chlorins and chlorophylls are addressed. The model allows for a quantification of these effects in some cases. Differences in the frontier orbital structure suggest that the [5,10,15,20 tetraaryl(alkyl)porphyrinato]metal complexes are sufficiently different from chlorophylls to be nonideal model compounds. These results are related to recent publications, and possible improvements of experimental and theory approaches are addressed.

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“…Conformationally gated electron transfer is observed in a variety of donor–acceptor pairs ranging from protein 38 and DNA 39,40 systems to molecular dyads. 41 Typically, donor–acceptor pairs with short alkyl linkers (<3) in which conformational motion gates the PET process will exhibit nanosecond lifetimes for electron transfer, 42,43 while longer linkers, such as polypeptides, have been observed to have gated electron transfer times in the tens of nanoseconds. 44 From these previous studies, we attribute our conformationally gated electron transfer to the flexible alkyl linker between the two metal centers.…”

Section: Resultsmentioning

confidence: 99%

Light-Activated Protein Inhibition through Photoinduced Electron Transfer of a Ruthenium(II)–Cobalt(III) Bimetallic Complex

et al. 2015

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We describe a mechanism of light activation that initiates protein inhibitory action of a biologically inert Co(III) Schiff base (Co(III)-sb) complex. Photoinduced electron transfer (PET) occurs from a Ru(II) bipyridal complex to a covalently attached Co(III) complex and is gated by conformational changes that occur in tens of nanoseconds. Reduction of the Co(III)-sb by PET initiates displacement of the inert axial imidazole ligands, promoting coordination to active site histidines of α-thrombin. Upon exposure to 455 nm light, the rate of ligand exchange with 4-methylimidazole, a histidine mimic, increases by approximately 5-fold, as observed by NMR spectroscopy. Similarly, the rate of α-thrombin inhibition increases over 5-fold upon irradiation. These results convey a strategy for light activation of inorganic therapeutic agents through PET utilizing redox-active metal centers.

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Light-Induced Electron Transfer in Pyropheophytin−Anthraquinone and Phytochlorin−Anthraquinone Dyads: Influence of Conformational Exchange

Cited by 28 publications

References 27 publications

Synthesis and Excited‐state Photodynamics of a Chlorin–Bacteriochlorin Dyad—Through‐space Versus Through‐bond Energy Transfer in Tetrapyrrole Arrays

Synthesis and Excited‐state Photodynamics of a Chlorin–Bacteriochlorin Dyad—Through‐space Versus Through‐bond Energy Transfer in Tetrapyrrole Arrays

The Role of the Electronic Structure of the Porphyrin as Viewed by EPR/ENDOR Methods in the Efficiency of Biomimetic Model Compounds for Photosynthesis

Light-Activated Protein Inhibition through Photoinduced Electron Transfer of a Ruthenium(II)–Cobalt(III) Bimetallic Complex

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