A Self-Assembled Two-Dimensional Zwitterionic Structure: H<sub>6</sub>TSPP Studied on Graphite

Friesen, Benjamin A.; Wiggins, Bryan; McHale, Jeanne L.; Mazur, Ursula; Hipps, K. W.

doi:10.1021/jp112086p

Cited by 37 publications

(35 citation statements)

References 65 publications

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“…Typically, molecules with such functional groups are deposited from an acidic solution on the substrate and can then be transferred into UHV for measurements. 28 Although in our experiments, molecular films were prepared by organic molecular beam deposition, a similar hydrogenation effect was found for metal-free tetra(hydroxyphenyl)porphyrin. The additional hydrogen atoms necessary to form H 4 THPP could originate from H 2 which is always present in vacuum or when the molecular powder was exposed to air.…”

Section: Protonation and Deprotonation At Nitrogen Atomssupporting

confidence: 74%

Photoelectron spectroscopy investigation of the temperature-induced deprotonation and substrate-mediated hydrogen transfer in a hydroxyphenyl-substituted porphyrin

et al. 2015

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The temperature dependent stepwise deprotonation of 5,10,15,20-tetra(p-hydroxyphenyl)porphyrin is investigated using photoelectron spectroscopy. An abundance of pyrrolic relative to iminic nitrogen and a decrease in the ratio of the amount of −NH− to −N= with increasing annealing temperature is found. In contrast to the molecules adsorbed on Au(111), on the more reactive Ag(110) surface, partial dissociation of the hydroxyl groups and subsequent diffusion and rebonding of hydrogen to the central nitrogen atoms resulting in a zwitterionic molecule was clearly observed. Moreover, partial C−H bond cleavage and the formation of new covalent bonds with adjacent molecules or the surface starts at a relatively high annealing temperature of 300 • C. This reaction is identified to occur at the carbon atoms of the pyrrole rings, which leads also to a shift in the N 1s signal and changes in the valence band of the molecules. Our results show that annealing can significantly alter the molecules which were deposited depending on the maximum temperature and the catalytic properties of the specific substrate. The thermal stability should be considered if a molecular monolayer is prepared from a multilayer by desorption, or if annealing is applied to enhance the self-assembly of molecular structures.

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Section: Protonation and Deprotonation At Nitrogen Atomssupporting

confidence: 74%

Photoelectron spectroscopy investigation of the temperature-induced deprotonation and substrate-mediated hydrogen transfer in a hydroxyphenyl-substituted porphyrin

et al. 2015

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“…(a)). This result is different from the case of graphitic surface, when a protonation of TPPS macrocycle was kept after an interaction. Thus, the atomic changes in TPPS macrocycle can be caused by a surface reactivity of the substrate, which is higher for single‐layer graphene in a comparison to graphite and some dielectric surfaces .…”

Section: Resultscontrasting

confidence: 71%

The interaction of iron and metal‐free meso‐tetra (4‐sulfonatophenyl) porphines with CVD graphene: a comparative Raman spectroscopy study

Naumenko

Grinceviciute

et al. 2014

J Raman Spectroscopy

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In this work, a non-covalent interaction of iron and metal-free meso-tetra (4-sulfonatophenyl) porphines (FeTPPS and TPPS, respectively) with high-quality single-layer graphene is studied by Raman spectroscopy. Such a kind of graphene functionalization is promising for a development of novel optoelectronic devices and sensors. Our results show that the central metal atom of porphyrin macrocycle, iron particularly, plays an important role in the integrity of FeTPPS on graphene surface; however, the predicted Raman enhancement is not significant. The interaction of metal-free TPPS with graphene leads to the deprotonation of TPPS molecules and higher Raman enhancement values. Moreover, initially deprotonated TPPS solutions after the adsorption onto the graphene surface demonstrate the appearance of new Raman bands and significantly enhanced Raman signals. We propose that a strong interaction between deprotonated TPPS and graphene is realized through pyrrole and desulfonated phenyl rings of closely located planar TPPS molecules on the graphene surface. The results show that both the protonation of porphyrin macrocycle and the existence of central metal atom are crucial for a formation of nanocomposites with defined electronic properties. Figure 2. Normalized Raman spectra of TPPS (a) and FeTPPS (b) films formed onto the glass substrates and the difference spectra (c) towards the ones of crystalline powders. The pH of initial solutions is displayed in the legend. The spectra are taken at an excitation wavelength of 532 nm, a laser power on the sample of 100 μW and an acquisition time of 120 s. The proposed molecular configurations of TPPS and FeTPPS at different pH are drawn using Jmol software and shown at the bottom of figure. (This figure is available in colour online at wileyonlinelibrary.com/journal/jrs) D. Naumenko et al. wileyonlinelibrary.com/journal/jrs

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“…This is a failure in the use of a simple model where it was assumed that only the sign of the polarization energy changed [25]. This failure is particularly large for porphyrins [13,25] where ionization energies measured from a thin film are nearly identical to those reported from the gas phase [60]. These discrepancies also occur with UPS observations (which agree with the OMTS), suggesting that the problem is in the model, not the technique.…”

Section: Resultsmentioning

confidence: 99%

“…Furthermore, Pc macrocycles are also known to self-aggregate by forming complex supramolecular assemblies having physical, chemical, electrical, and optical properties different from the discrete molecular units [10][11][12]. Once these molecular materials are deposited onto an electrode surface (via physisorption or chemisorption) a significant redistribution of electron density in either the molecule/ aggregate system or at the adsorbate/electrode interface may result, significantly altering device performance [13,14]. Thus, the knowledge of oxidation and reduction states, the location of the conduction bands, and the bias dependence and mechanism of electrochemical processes of the Pc adsorbates at the substrate interface becomes a crucial prerequisite for their use in electronic devices.…”

Section: Introductionmentioning

confidence: 99%

Electron affinity states of metal supported phthalocyanines measured by tunneling spectroscopy

Hipps

Mazur

2012

J. Porphyrins Phthalocyanines

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Orbital Mediated Tunneling Spectroscopy OMTS (elastic electron tunneling) was employed in measuring electron affinity levels (EA) of unsubstituted, alkylated, sulfonated, and metalated phthalocyanines (Pc) adsorbed as single molecules or aggregates on metal substrates and imbedded in metal-insulator-metal (M-I-M) devices. MPc complexes were vapor deposited, solution phase doped, or transferred as Langmuir–Blodgett films. It was determined that while the nature of the substituents has a large effect on the gas phase electron affinities, they play a minimal role on the electron affinities of metal supported phthalocyanines. Moreover, the orientation of monolayer films and the method of film deposition (vapor, solution, Langmuir–Blodgett) also appear to play only a minor role in determining the electron affinities. Electrochemical reduction potentials obtained for the solution phase molecular systems are compared to the OMTS data and a strong correlation is observed. In contrast, the predicted EA values for the gas phase molecules show little correspondence with their OMTS equivalents for adsorbed phthalocyanines. Inelastic scattering from phthalocyanine π→π* transitions and metal centered d–d transitions are observed for chromophores imbedded in tunnel diodes. Both the observed lowest spin forbidden transitions and the calculated gas phase HOMO–LUMO gaps are only weakly affected by Pc substitution and surface orientation.

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A Self-Assembled Two-Dimensional Zwitterionic Structure: H₆TSPP Studied on Graphite

Cited by 37 publications

References 65 publications

Photoelectron spectroscopy investigation of the temperature-induced deprotonation and substrate-mediated hydrogen transfer in a hydroxyphenyl-substituted porphyrin

Photoelectron spectroscopy investigation of the temperature-induced deprotonation and substrate-mediated hydrogen transfer in a hydroxyphenyl-substituted porphyrin

The interaction of iron and metal‐free meso‐tetra (4‐sulfonatophenyl) porphines with CVD graphene: a comparative Raman spectroscopy study

Electron affinity states of metal supported phthalocyanines measured by tunneling spectroscopy

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A Self-Assembled Two-Dimensional Zwitterionic Structure: H6TSPP Studied on Graphite

Cited by 37 publications

References 65 publications

Photoelectron spectroscopy investigation of the temperature-induced deprotonation and substrate-mediated hydrogen transfer in a hydroxyphenyl-substituted porphyrin

Photoelectron spectroscopy investigation of the temperature-induced deprotonation and substrate-mediated hydrogen transfer in a hydroxyphenyl-substituted porphyrin

The interaction of iron and metal‐free meso‐tetra (4‐sulfonatophenyl) porphines with CVD graphene: a comparative Raman spectroscopy study

Electron affinity states of metal supported phthalocyanines measured by tunneling spectroscopy

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A Self-Assembled Two-Dimensional Zwitterionic Structure: H₆TSPP Studied on Graphite