Dependence of electron transfer rates on donor-acceptor angle in bis-porphyrin adducts

Helms, Anna M.; Heiler, David; McLendon, George

doi:10.1021/ja00011a042

Cited by 142 publications

(131 citation statements)

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“…Surprisingly, we see an anodic shift in E pa for TTP and PAP, with TTP shifted by 130 mV and PAP by 240 mV relative to TMP. McLendon and coworkers offer a possible explanation for this behavior (37). In bridged porphyrin adducts, they observe maximum rates of intramolecular electron transfer at 0°and 90°, with the minimum rate near 45°.…”

Section: Discussionmentioning

confidence: 98%

Metal-free organic sensitizers for use in water-splitting dye-sensitized photoelectrochemical cells

Swierk¹,

Méndez-Hernández

McCool³

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

140

107

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Solar fuel generation requires the efficient capture and conversion of visible light. In both natural and artificial systems, molecular sensitizers can be tuned to capture, convert, and transfer visible light energy. We demonstrate that a series of metal-free porphyrins can drive photoelectrochemical water splitting under broadband and red light (λ > 590 nm) illumination in a dye-sensitized TiO2 solar cell. We report the synthesis, spectral, and electrochemical properties of the sensitizers. Despite slow recombination of photoinjected electrons with oxidized porphyrins, photocurrents are low because of low injection yields and slow electron self-exchange between oxidized porphyrins. The free-base porphyrins are stable under conditions of water photoelectrolysis and in some cases photovoltages in excess of 1 V are observed.

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Section: Discussionmentioning

confidence: 98%

Metal-free organic sensitizers for use in water-splitting dye-sensitized photoelectrochemical cells

Swierk¹,

Méndez-Hernández

McCool³

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

140

107

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“…Electron transfer proceeded most efficiently at angles of 0°and 90°and was least efficient at a dihedral angle of 50°. 23 Wang et al examined the dependence of electron transfer on rotational motion for an asymmetric carboxylic acid dendrimer with a single ferrocene postioned "off-center" in the dendrimer structure. 24 At a neutral pH, the surface of the dendrimer is highly negative and favors an orientation with the ferrocene pointed away from the electrode surface.…”

Section: Discussionmentioning

confidence: 99%

Effect of Rotational Mobility on Photoelectron Transfer: Comparison of Two Zeolite Topologies

2003

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Nuclear magnetic resonance (NMR) spectroscopy and time-resolved diffuse reflectance (TRDR) have been combined to study the effects of constrained rotational motion on the rates of photoinduced electron-transfer reactions within zeolites. By synthesizing tris(2,2′-bipyridine) ruthenium (II) [Ru(bpy) 3 2+ ] within the large cages of zeolites Y and EMT, it was possible to directly investigate the effect of zeolite cage size on molecular motion of Ru(bpy) 3 2+ and the influence of the cage size on the rate of intrazeolitic electron transfer. Deuterium solid-state NMR shows that zeolite Y imposes restraint on molecular rotation of Ru(bpy) 3 2+ , while zeolite EMT allows for motion. Temperature-dependent studies show the ability to freeze or induce motion of Ru-(bpy) 3 2+ within zeolite EMT while motion within zeolite Y remains unaffected, even at elevated temperatures. For zeolite EMT, an increase in the rate of the photoinduced forward and back electron transfer from Ru-(bpy) 3 2+ to methyl viologen was noted and correlated with access, rotational motion, and favorable orbital overlap. The overall photochemical charge separation efficiencies for the intrazeolitic Ru(bpy) 3 2+ -bipyridinium reactions were similar for both zeolites. IntroductionOne of the major obstacles in the development of artificial photosynthetic systems is that the thermal back-electron transfer reaction negates the utilization of photochemically created reactive redox species. 1 Thus, considerable effort is being made to understand the features that control electron-transfer dynamics. Toward that end, many donor-acceptor systems have been examined, and assembly of molecular units on microheterogeneous supports is being pursued to influence electron-transfer dynamics. 2 By virtue of the nature of microheterogeneous supports, the motion of molecules is modified and it is of interest to examine how electron transfer is influenced by such immobilization. Zeolites, because of the molecular size of their cavities, are an excellent host system to investigate immobilization phenomena.Zeolite Y consists of a regular network of sodalite cages in a tetrahedral arrangement resulting in 13 Å supercages with 7 Å windows (Figure 1a). 3 This is large enough to accommodate the luminescent molecule trisbipyridine ruthenium (II) [Ru-(bpy) 3 2+ ] which has a molecular diameter of 12 Å and can be assembled within the supercages by using a "ship-in-a-bottle" synthetic procedure. 4 These intrazeolitic ruthenium complexes can then be surrounded by bipyridinium ions such as methyl viologen (MV 2+ ) using the inherent ion-exchange properties of the zeolite. It has been shown that zeolite Y can promote longlived, Ru(bpy) 3 3+ -bipyridinium radical cation charge-separated states. 5,6 Molecular modeling of Ru(bpy) 3 2+ entrapped within zeolite Y indicated a significant number of contacts between the metal complex and the walls of the zeolite that were within the van der Waals radii of the atoms. 6 It was proposed that these contacts inhibit the rotational motion of the i...

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“…Another important point is the electron density in the phenyl ring of the biphenylic system, since it also affects the transport properties of the biphenyl. [267] For all this reasons In comparison to previously reported azo functionalized small ring systems [47][77] [182] and based on preliminary calculations, a macrocycle with a small CH 2 linker is flexible enough to allow the optically triggered cis/trans isomerization reaction.…”

Section: Figure 57mentioning

confidence: 99%

“…[163] The physical properties of biphenyls can be altered by different parameters. In particular the electron density in the phenyl rings [267] and the torsion angle between both phenyl rings play an important role in the transport properties through a biphenylic system. [157][177] [179] The systematic variation of the torsion angle ( in biphenyl subunits with almost negligible alterations in electronic properties of the phenyl rings was found to show a linear correlation of the single molecule conductance with the cos 2 of the torsion angle.…”

Section: Switchable Conducting Azo Biphenylsmentioning

confidence: 99%

Shape‐Switchable Azo‐Macrocycles

et al. 2009

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The synthesis of four shape‐switchable macrocycles comprising different peripheral substituents is described. The macrocycles 1–4 consist of m‐terphenyl semicircles interlinked by two azo joints. These macrocycles were assembled from nitro‐functionalized m‐terphenyl moieties through reductive dimerization. The semicircles were assembled through Suzuki cross‐coupling reactions. The molecular weights of the macrocycles were determined by vapour pressure osmometry, because mass spectrometry failed in the cases of 2 and 3. The E → Z photoisomerization reactions were analysed by UV/Vis spectroscopy complemented by 1H NMR studies. A very slow thermal back‐reaction indicated considerable stabilization of the Z isomer. The reduced efficiency of the thermal back‐reaction probably arises from the reduced degree of freedom due to the mechanical interlinking of the two azo groups. The photostationary state consisted of all‐Z (85 %) and all‐E isomers (15 %). The E → Z transformation induced by irradiation displayed simple exponential kinetics, which indicates pairwise switching of the two azo groups in a macrocycle, at least on the timescale under investigation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

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Dependence of electron transfer rates on donor-acceptor angle in bis-porphyrin adducts

Cited by 142 publications

References 0 publications

Metal-free organic sensitizers for use in water-splitting dye-sensitized photoelectrochemical cells

Metal-free organic sensitizers for use in water-splitting dye-sensitized photoelectrochemical cells

Effect of Rotational Mobility on Photoelectron Transfer: Comparison of Two Zeolite Topologies

Shape‐Switchable Azo‐Macrocycles

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