Correlation of Frontier Orbital Positions and Conduction Type of Molecular Semiconductors As Derived from UPS in Combination with Electrical and Photoelectrochemical Experiments

Schlettwein, Derck; Armstrong, Neal R.

doi:10.1021/j100096a023

Cited by 85 publications

(36 citation statements)

References 14 publications

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“…Armstrong and co-workers have also noticed this difficulty in reconciling solution-phase oxidation potentials with thin-film UPS data (33,34). Armstrong and co-workers have also noticed this difficulty in reconciling solution-phase oxidation potentials with thin-film UPS data (33,34).…”

Section: Stm-based Tunneling Spectra and Ultraviolet Photoemission Spmentioning

confidence: 99%

Electron Tunneling, a Quantum Probe for the Quantum World of Nanotechnology

Hipps

Scudiero

2005

J. Chem. Educ.

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The world of the nanoscale is exciting because it is governed by rules different from those we know in the macroscopic, or even microscopic, realm. It is a world where quantum mechanics dominates the scene and events occuring at the scale of a single molecule, or even a single atom, are critical. What we know about the behavior of material on our scale is no longer true on the nanometer scale. In order to study this quantum world, a quantum-mechanical probe is essential. Electron tunneling provides that quantum mechanical tool.In the Newtonian world, a particle can never be in a region where its potential energy is greater than its total energy. To do so would require a negative kinetic energy-a clear impossibility since mv 2 ͞2 ≥ 0. As the scale shrinks to molecular dimensions, of the order of one nanometer, classical concepts fail and quantum mechanics takes over. Thus, it is possible for a particle to move from one classically allowed region to another through a very small region where its potential energy is greater than its total energy-this is the phenomenon of tunneling. While it can occur for relatively heavy particles such as protons, it is far more common for electrons. Electron tunneling is a particularly useful probe because it is easy to control the flow and energy of electrons and to set up precisely controlled regions through which the electron must tunnel. An early example of an electron-tunneling device was the metal-insulator-metal (M-I-M) tun-nel diode, as shown in Figure 1 (1-5). 1 Also shown in Figure 1 are the equivalent features of a scanning tunneling microscope (STM) (6-9). Both devices rely on exactly the same physics. Within the conductors (metal electrodes in the M-I-M´ case, substrate and atomically sharp tip in the STM case) the electrons are in classically allowed regions I and IIItheir total energy E is greater than their potential energy. In the gap between conductors (the insulator in the M-I-Mć ase, the vacuum or solvent gap in the STM case) however, there is a potential region, region II, where they are classically forbidden but quantum mechanically allowed. A simple quantum mechanical calculation quickly demonstrates that the probability of transmission through the barrier decreases exponentially with the thickness of the barrier and the square root of the height relative to the electron energy. If distance, d, is measured in Angstroms (0.1 nm) and energies (E and U ) are measured in electron volts, then the constant A in Figure 1 is approximately one (5-6).We note that STM has been thoroughly discussed and reviewed (6-8), including in the pages of this Journal (7). Thus, we will assume that the reader is reasonably familiar with the basic aspects of STM imaging. Specific examples of STM-based spectroscopy will be drawn from porphyrins and phthalocyanines on Au(111). These metal-organic systems share the characteristics of good chemical and thermal stability and a rich spectrum of both filled and empty states. Figure 1. Schematic drawings of (A) a tunnel diode, (B) STM, and (...

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Section: Stm-based Tunneling Spectra and Ultraviolet Photoemission Spmentioning

confidence: 99%

Electron Tunneling, a Quantum Probe for the Quantum World of Nanotechnology

Hipps

Scudiero

2005

J. Chem. Educ.

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“…The peak located at E b ) -1.25 eV was attributed to the highest occupied molecular orbital (HOMO) state of ZnPC adsorbed on the TiO 2 (110) surface. 27 In the case of the ZnPC-thick film, the work function was further decreased to Φ ) 4.01 eV. In addition, the binding energy of the HOMO state shifted to E b ) -1.40 eV and its bandwidth decreased by 0.12 eV (fwhm) in comparison with the ultrathin film.…”

Section: Electronicmentioning

confidence: 92%

Electron Transfer Dynamics from Organic Adsorbate to a Semiconductor Surface: Zinc Phthalocyanine on TiO₂(110)

et al. 2005

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The femtosecond time evolutions of excited states in zinc phthalocyanine (ZnPC) films and at the interface with TiO2(110) have been studied by using time-resolved two-photon photoelectron spectroscopy (TR-2PPE). The excited states are prepared in the first singlet excited state (S1) with excess vibrational energy. Two different films are examined: ultrathin (monolayer) and thick films of approximately 30 A in thickness. The decay behavior depends on the thickness of the film. In the case of the thick film, TR-2PPE spectra are dominated by the signals from ZnPC in the film. The excited states decay with tau = 118 fs mainly by intramolecular vibrational relaxation. After the excited states cascaded down to near the bottom of the S1 manifold, they decay slowly (tau = 56 ps) although the states are located at above the conduction band minimum of the bulk TiO2. The exciton migration in the thick film is the rate-determining step for the electron transfer from the film to the bulk TiO2. In the case of the ultrathin film, the contribution of electron transfer is more evident. The excited states decay faster than those in the thick film, because the electron transfer competes with the intramolecular relaxation processes. The electronic coupling with empty bands in the conduction band of TiO2 plays an important role in the electron transfer. The lower limit of the electron-transfer rate was estimated to be 1/296 fs(-1). After the excited states relax to the states whose energy is below the conduction band minimum of TiO2, they decay much more slowly because the electron-transfer channel is not available for these states.

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“…However, many phthalocyanine complexes remain aggregated even in non-aqueous solutions. [15][16][17] Aromatic solvents such as benzene or toluene are known to give narrow Q bands in phthalocyanines spectra whereas broadening is observed in other non-aromatic solvents. Solvents also affect the photophysical and photochemical properties of MPc complexes.…”

Section: 14mentioning

confidence: 99%

Absorbtion Spectroscopy, Molecular Dynamics Calculations, and Multivariate Curve Resolution on the Phthalocyanine Aggregation

Ajloo¹,

Ghadamgahi²,

Shaheri³

et al. 2014

Bulletin of the Korean Chemical Society

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Co(II)-tetrasulfonated phthalocyanine (CoTSP) is known to be aggregated to dimer at high concentration levels in water. A study on the aggregation of CoTSP using multivariate curve resolution analysis of the visible absorbance spectra over a concentration range of 30, 40 and 50 µM in the presence of dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), acetonitrile (AN) and ethanol (EtOH) in the concentration range of 0 to 3.57 M is conducted. A hard modeling-based multivariate curve resolution method was applied to determine the dissociation constants of the CoTSP aggregates at various temperatures ranging from 25, 45 and 65°C and in the presence of various co-solvents. Dissociation constant for aggregation was increased and then decrease by temperature and concentration of phthalocyanine, respectively. Utilizing the vant Hoff relation, the enthalpy and entropy of the dissociation equilibriums were calculated. For the dissociation of both aggregates, the enthalpy and entropy changes were positive and negative, respectively. Molecular dynamics simulation of cosolvent effect on CoTSP aggregation was done to confirm spectroscopy results. Results of radial distribution function (RDF), root mean square deviation (RMSD) and distance curves confirmed more effect of polar solvent to decrease monomer formation.

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Correlation of Frontier Orbital Positions and Conduction Type of Molecular Semiconductors As Derived from UPS in Combination with Electrical and Photoelectrochemical Experiments

Cited by 85 publications

References 14 publications

Electron Tunneling, a Quantum Probe for the Quantum World of Nanotechnology

Electron Tunneling, a Quantum Probe for the Quantum World of Nanotechnology

Electron Transfer Dynamics from Organic Adsorbate to a Semiconductor Surface: Zinc Phthalocyanine on TiO₂(110)

Absorbtion Spectroscopy, Molecular Dynamics Calculations, and Multivariate Curve Resolution on the Phthalocyanine Aggregation

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Correlation of Frontier Orbital Positions and Conduction Type of Molecular Semiconductors As Derived from UPS in Combination with Electrical and Photoelectrochemical Experiments

Cited by 85 publications

References 14 publications

Electron Tunneling, a Quantum Probe for the Quantum World of Nanotechnology

Electron Tunneling, a Quantum Probe for the Quantum World of Nanotechnology

Electron Transfer Dynamics from Organic Adsorbate to a Semiconductor Surface: Zinc Phthalocyanine on TiO2(110)

Absorbtion Spectroscopy, Molecular Dynamics Calculations, and Multivariate Curve Resolution on the Phthalocyanine Aggregation

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Product

Resources

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Electron Transfer Dynamics from Organic Adsorbate to a Semiconductor Surface: Zinc Phthalocyanine on TiO₂(110)