Kinetics of lateral electron hopping in osmium-tris-4,7- diphenylphenanthroline perchlorate monolayers at the air/water interface

Charych, Deborah H.; Anvar, David J.; Majda, Marcin

doi:10.1016/0040-6090(94)90491-x

Cited by 20 publications

(21 citation statements)

References 16 publications

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“…( 3) yields a self-exchange rate constant of 4.45 Â 10 7 M À1 s À1 . This value is comparable with those reported for osmium poly-pyridyl complexes in solution, 24 or within monolayers, [25][26][27] which supports our interpretation that electron self-exchange represents the rate determining step where the supporting electrolyte is sodium perchlorate. This contrasts sharply with that found for solid deposits of [Os(bpy) 2 3,5-bis(pyridin-4-yl)-1,2,4,-triazole Cl] where anion transport limited the overall rate of charge transport.…”

Section: Effect Of Electrolyte Concentration On D Appsupporting

confidence: 91%

Impact of ion solvation on charge transport through [Os(bpy)2 (H2tzt) Cl]+ in the solid state

Forster

Mulledy

Walsh

et al. 2004

Phys. Chem. Chem. Phys.

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Microcavities have been formed at the tip of platinum microelectrodes and packed with [Os(bpy) 2 (H 2 tzt) Cl]PF 6 , where bpy is 2,2 0 -bipyridyl and H 2 tzt is 3,6-bis(4-pyridyl)-dihydro-1,2,4,5-tetrazine. These solid deposits exhibit well defined electrochemical responses associated with the Os 2þ/3þ redox couple where the identity of the electrolyte anion is sodium perchlorate, bromide, chloride, iodide, fluoride or nitrate. Scanning electron microscopy of deposits on planar electrodes reveals that voltammetric cycling triggers morphological changes that depend on the identity of the electrolyte anion. The formal potential of the Os 2þ/3þ redox process ranges from 0.225 AE 0.015 V (perchlorate) to 0.390 AE 0.010 V (fluoride) and depends approximately linearly on the hydration energy of the anion. This result suggests that weakly hydrated anions are thermodynamically easier to incorporate within the solid deposit in response to redox switching, i.e., the anion desolvation energy influences the energetics of redox switching. Cyclic voltammetry has been used to determine the apparent charge transport diffusion coefficient, D CT , describing homogeneous charge transport through the deposit. The rates of charge transport depend significantly on the identity and concentration of the supporting electrolyte ranging from a minimum of 3.1 AE 0.5 Â 10 À12 cm 2 s À1 in 0.1 M NaF to a maximum of 1.1 AE 0.1 Â 10 À10 cm 2 s À1 in 1.0 M NaClO 4 . In NaClO 4 supporting electrolyte, D CT is independent of the electrolyte concentration from 0.1 to 1.0 M suggesting that electron self-exchange between adjacent redox centres limits the overall rate of charge transport through the solid. In contrast, in NaBr solutions D CT is sensitive to the electrolyte concentration increasing from 0.2 AE 0.01 to 7.9 AE 0.1 Â 10 À11 cm 2 s À1 on going from 0.1 to 1.0 M suggesting that the availability of charge compensating counterions within the solid limits the rate of charge transport. The free energy of at least partially desolvating charge compensating counterions prior to their incorporation within the oxidised deposit appears to control both the energetics and dynamics of charge transport.

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Section: Effect Of Electrolyte Concentration On D Appsupporting

confidence: 91%

Impact of ion solvation on charge transport through [Os(bpy)2 (H2tzt) Cl]+ in the solid state

Forster

Mulledy

Walsh

et al. 2004

Phys. Chem. Chem. Phys.

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“…When the concentration of Fe(CN) 5 was varied, a percolation threshold appeared, below which the electroactive fraction of the redox centers sharply dropped to zero. Two-dimensional percolation behavior was observed by Majda et al in a Langmuir monolayer of an osmium complex diluted by 1-octadecanol at the water surface. The apparent diffusion coefficient decreased rapidly from 2.4 × 10 5 m 2 s -1 to 0 as the mole fraction of the electroactive species was reduced from 1 to 0.6.…”

Section: Introductionmentioning

confidence: 81%

Efficient Lateral Electron Transport inside a Monolayer of Aromatic Amines Anchored on Nanocrystalline Metal Oxide Films

et al. 1998

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A monolayer of a phosphonated triarylamine adsorbed on nanocrystalline TiO2, ZrO2, or Al2O3 film deposited on conducting glass displays reversible electrochemical and electrochromic behavior although the redox potential of the electroactive molecules (0.80 V vs NHE) lies in the forbidden band of the semiconducting or insulating oxides. The mechanism of charge transport was found to involve hole injection from the conducting support followed by lateral electron hopping within the monolayer. The apparent diffusion coefficient ranged from 2.8 × 10(-12) m(2) s(-1) in the neat 1-ethyl-2-methylimidazolium bis(trifluoromethylsulfonyl)imide (EtMeIm(+)Tf2N(-)) to 1.1 × 10(-11) m(2) s(-1) in acetonitrile + 2 M EtMeIm(+)Tf2N(-). A percolation threshold for electronic conductivity was found at a surface coverage corresponding to 50% of a full monolayer.

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“…1-10 µm diameter). Since we observed earlier that the kinetics of the lateral electron hopping measured in the compressed Os-(DPP) 3 monolayers decreases significantly with the size of the initially formed aggregates, 22 all monolayer films were spread from 0.20 mM chloroform solutions.…”

Section: Resultsmentioning

confidence: 99%

“…As demonstrated earlier, while Os(DPP) 3 is not an amphiphilic molecule, its chloroform solutions can be spread on a perchloric acid subphase where it forms stable monolayer films. 22 Brewster angle microscopy revealed that, immediately upon spreading (mean molecular area of 360…”

Section: Resultsmentioning

confidence: 99%

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Structure and Lateral Electron Hopping in Osmium-tris-4,7-diphenylphenanthroline Perchlorate Monolayers at the Air/Water Interface

et al. 1999

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Osmium tris-diphenylphenanthroline perchlorate (Os(DPP) 3 ) can be spread at the air/water interface where it forms solid monolayer films. Brewster angle microscopy revealed that these films consist of irregular ca. 100 to 1000 µm diameter 2D aggregates which coalesce upon compression to form continuous films. Grazing incidence X-ray diffraction data showed that the structure of the aggregates is independent of the degree of monolayer compression and features a 2D lattice of hexagonally close-packed Os(DPP) 3 centers with Os-Os distances of 12.57 Å. The latter is 4 to 24% shorter than the Ru-Ru distances found in the 3D monoclinic crystal of an isostructural Ru (DPP) 3 . Two dimensional electrochemical measurements carried out with line microelectrodes at the air/water interface were used to study kinetics of the lateral electron transport in these Langmuir monolayers. Electron transport involves electron hopping on the 2D lattice of the osmium sites where the individual electron transfer steps between Os II (DPP) 3 and Os III (DPP) 3 take place with the rate constant k 1 ) 4.7 × 10 8 s -1 . Percolation theory was used to account for the observed increase of the electron hopping rates during monolayer compression on the water surface resulting in an increase of the extent of connectivity and thus electroactivity of the initially formed 2D Os(DPP) 3 aggregates. Percolation theory also accounts well for the dependence of the electron hopping rates on the composition of fully compressed Os-(DPP) 3 /Ru(DPP) 3 monolayers in which the ruthenium species were used to homogeneously dilute the Os-(DPP) 3 sites. In contrast, in Os(DPP) 3 /octadecanol monolayers, macroscopic self-segregation of the two components was inferred from a larger positive shift of the apparent percolation threshold in the lateral electron hopping.

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Kinetics of lateral electron hopping in osmium-tris-4,7- diphenylphenanthroline perchlorate monolayers at the air/water interface

Cited by 20 publications

References 16 publications

Impact of ion solvation on charge transport through [Os(bpy)2 (H2tzt) Cl]+ in the solid state

Impact of ion solvation on charge transport through [Os(bpy)2 (H2tzt) Cl]+ in the solid state

Efficient Lateral Electron Transport inside a Monolayer of Aromatic Amines Anchored on Nanocrystalline Metal Oxide Films

Structure and Lateral Electron Hopping in Osmium-tris-4,7-diphenylphenanthroline Perchlorate Monolayers at the Air/Water Interface

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