Adsorption of Hexylferrocene Phosphonic Acid on Indium−Tin Oxide Electrodes. Evidence of Strong Interchain Interactions in Ferrocene Self-Assembled Monolayers

Vercelli, Barbara; Zotti, Gianni; Schiavon, and Gilberto; Zecchin, Sandro; Berlin, Anna

doi:10.1021/la030150y

Cited by 43 publications

(53 citation statements)

References 32 publications

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“…This value is close to the one previously obtained from the adsorption of the ferrocenylhexylphosphonic acid at an ITO electrode in ethanol. 52 It is however much lower than the value of 660 pmol cm −2 reported for the chemical functionalization of ITO by ferrocenyltrichlorosilylbutane in toluene 54 and also more than half the theoretical maximal coverage expected for a densely packed monolayer of ferrocenyl groups on a perfectly flat surface (i.e., 450 pmol cm −2 ). 51 The surface coverages of the adsorbed ferrocenyl derivatives at R-ITO electrodes were monitored for their temporal stability by CV as a function of soaking time in a ferrocenyl-free Hepes buffer.…”

Section: ■ Resultsmentioning

confidence: 77%

Efficient Chemisorption of Organophosphorous Redox Probes on Indium Tin Oxide Surfaces under Mild Conditions

2015

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We report a mild and straightforward one-step chemical surface functionalization of indium tin oxide (ITO) electrodes by redox-active molecules bearing an organophosphoryl anchoring group (i.e., alkyl phosphate or alkyl phosphonate group). The method takes advantage of simple passive adsorption in an aqueous solution at room temperature. We show that organophosphorus compounds can adsorb much more strongly and stably on an ITO surface than analogous redox-active molecules bearing a carboxylate or a boronate moiety. We provide evidence, through quantitative electrochemical characterization (i.e., by cyclic voltammetry) of the adsorbed organophosphoryl redox-active molecules, of the occurrence of three different adsorbate fractions on ITO, exhibiting different stabilities on the surface. Among these three fractions, one is observed to be strongly chemisorbed, exhibiting high stability and resistance to desorption/hydrolysis in a free-redox probe aqueous buffer. We attribute this remarkable stability to the formation of chemical bonds between the organophosphorus anchoring group and the metal oxide surface, likely occurring through a heterocondensation reaction in water. From XPS analysis, we also demonstrate that the surface coverage of the chemisorbed molecules is highly affected by the degree of surface hydroxylation, a parameter that can be tuned by simply preconditioning the freshly cleaned ITO surfaces in water. The lower the relative surface hydroxide density on ITO, the higher was the surface coverage of the chemisorbed species. This behavior is in line with a chemisorption mechanism involving coordination of a deprotonated phosphoryl oxygen atom to the non-hydroxylated acidic metal sites of ITO.

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Section: ■ Resultsmentioning

confidence: 77%

Efficient Chemisorption of Organophosphorous Redox Probes on Indium Tin Oxide Surfaces under Mild Conditions

2015

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“…Organization of the porphyrin dimer as a "special pair" mimic ZnA C H T U N G T R E N N U N G (ImPPO 3 ) monolayer formation: The ITO glass was immersed in a 1.0 mm solution of H 2 A C H T U N G T R E N N U N G (ImPPO 3 ) in ethanol at room temperature for 40 h. [30] Thereafter, the substrate was washed with ethanol and dichloromethane, and dried under a stream of nitrogen. The porphyrin incorporated into the SAM was metalated by gently refluxing at 50 8C for 2 h in CHCl 3 (4 mL) containing 0.2 mL of a saturated solution of zinc acetate in MeOH.…”

Section: Resultsmentioning

confidence: 99%

Efficient Charge Injection from the S₂ Photoexcited State of Special‐Pair Mimic Porphyrin Assemblies Anchored on a Titanium‐Modified ITO Anode

Morisue

Haruta

Kalita

et al. 2006

Chemistry A European J

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A novel surface fabrication methodology has been accomplished, aimed at efficient anodic photocurrent generation by a photoexcited porphyrin on an ITO (indium-tin oxide) electrode. The ITO electrode was submitted to a surface sol-gel process with titanium n-butoxide in order to deposit a titanium monolayer. Subsequently, porphyrins were assembled as monolayers on the titanium-treated ITO surface via phosphonate, isophthalate, and thiolate groups. Slipped-cofacial porphyrin dimers, the so-called artificial special pair at the photoreaction center, were organized through imidazolyl-to-zinc complementary coordination of imidazolylporphyrinatozinc(II) units, which were covalently immobilized by ring-closing olefin metathesis of allyl side chains. The modified surfaces were analyzed by means of X-ray photoelectron spectroscopy. Photoirradiation of the porphyrin dimer generated a large anodic photocurrent in aqueous electrolyte solution containing hydroquinone as an electron sacrificer, due to the small reorganization energy of the dimer. The use of different linker groups led to significant differences in the efficiencies of anodic photocurrent generation. The apparent flat-band potentials evaluated from the photocurrent properties at various pH values and under biased conditions imply that the band structure of the ITO electrode is modified by the anchoring species. The quantum yield for the anodic photocurrent generation by photoexcitation at the Soret band is increased to 15 %, a surprisingly high value without a redox cascade structure on the ITO electrode surface, while excitation at the Q band is not so significant. Extensive exploration of the photocurrent properties has revealed that hot injection of the photoexcited electron from the S2 level into the conduction band of the ITO electrode takes place before internal conversion to the S1* state, through the strong electronic communication of the phosphonyl anchor with the sol-gel-modified ITO surface.

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“…Adsorption of hexylferrocene phosphonic acid (Fc[(CH 2 ) 6 PO(OH) 2 ]) has been investigated by Vercelli et al from ethanol to silanized and unsilanized ITO surfaces[77]. A maximum surface coverage was obtained at 4.2 × 10 −10 mols cm −2 , approximately four times the surface coverage obtained with the analogous carboxylated ferrocene.…”

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Modification of Transparent Conducting Oxide ( TCO ) Electrodes through Silanization and Chemisorption of Small Molecules

Brumbach

Armstrong

2007

Encyclopedia of Electrochemistry

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The sections in this article are Introduction The Metal Oxide Electrode and Modification Schemes Commonly Encountered TCO Electrodes Variability in TCO Electrodes Factors that Control the Surface Composition of the TCO Electrode Chemical Modification of TCO Surfaces Using Silane Chemistries Introduction to Silane Modification Examples of Silane Modification Silane Modification of Electrodes for Use in Devices Modification of TCO Surfaces through Chemisorption of Small Molecules Modification using Small Molecules Containing Carboxylic Acid Functionality Modification Using Phosphonic Acids and Other Chemisorbing Functionalities Conclusions Acknowledgments

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Adsorption of Hexylferrocene Phosphonic Acid on Indium−Tin Oxide Electrodes. Evidence of Strong Interchain Interactions in Ferrocene Self-Assembled Monolayers

Cited by 43 publications

References 32 publications

Efficient Chemisorption of Organophosphorous Redox Probes on Indium Tin Oxide Surfaces under Mild Conditions

Efficient Chemisorption of Organophosphorous Redox Probes on Indium Tin Oxide Surfaces under Mild Conditions

Efficient Charge Injection from the S₂ Photoexcited State of Special‐Pair Mimic Porphyrin Assemblies Anchored on a Titanium‐Modified ITO Anode

Modification of Transparent Conducting Oxide ( TCO ) Electrodes through Silanization and Chemisorption of Small Molecules

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Adsorption of Hexylferrocene Phosphonic Acid on Indium−Tin Oxide Electrodes. Evidence of Strong Interchain Interactions in Ferrocene Self-Assembled Monolayers

Cited by 43 publications

References 32 publications

Efficient Chemisorption of Organophosphorous Redox Probes on Indium Tin Oxide Surfaces under Mild Conditions

Efficient Chemisorption of Organophosphorous Redox Probes on Indium Tin Oxide Surfaces under Mild Conditions

Efficient Charge Injection from the S2 Photoexcited State of Special‐Pair Mimic Porphyrin Assemblies Anchored on a Titanium‐Modified ITO Anode

Modification of Transparent Conducting Oxide ( TCO ) Electrodes through Silanization and Chemisorption of Small Molecules

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Efficient Charge Injection from the S₂ Photoexcited State of Special‐Pair Mimic Porphyrin Assemblies Anchored on a Titanium‐Modified ITO Anode