Gas-phase Ionization Potentials Research Articles

Chain-length dependence of electronic and electrochemical properties of conjugated systems: polyacetylene, polyphenylene, polythiophene, and polypyrrole

The valence effective Hamiltonian (VEH) technique is used to compute ionization potentials, optical transition energies, and electron affinities of oligomers and polymers in four conjugated systems: polyacetylene, poly@-phenylene), polythiophene, and polypyrrole. The theoretical results compare very favorably with experimental data on gas-phase ionization potentials, optical absorption, and electrochemical redox potentials. The latter case is especially important, and the calculated oxidation and reduction potentials are in remarkably good agreement with experiment. For polyacetylene the predicted oxidation potential is 0.4 V vs. SCE, and the predicted reduction potential is -1.1 V, both of which are in good agreement with experimentally observed oxidation and reduction onsets. In these systems, the electronic and electrochemical properties predicted by VEH theory for the oligomers extrapolate to those of the polymer with an inverse chain-length dependence.

Electrochemical and ESR kinetics studies of electron transfer in the system bis(η 6-Arene)Chromium(0)/bis(η 6-Arene)Chromium(I)

The self-exchange rates and activation parameters in the (η 6-arene) 2Cr 0/(η 6- arene) 2Cr I systems (where arene = toluene, benzene, methoxylbenzene, biphenyl, ethylbenzoate and chlorobenzene) have been measured by the ESR line broaden ing technique in DMSO solvent. The one-electron reduction was investigated by cyclic voltammetry for the series of substituted complexes of (η 6-arene) 2Cr I. A linear correlation was obtained between the measured E 1/2 values and the sum of Hammett parameters, Σσ m. For a series of solvents, a linear relationship between log k (the exchange rate constant of (biph) 2Cr 0/+1) and ( 1 n 2 -1 D s ) where n 2 and D s are the optical and static dielectric constants of the solvent medium, respectively, has been observed. This linearity is predicted by Marcus treatment for outer-sphere electron transfer process. A correlation of the oxidation stability of sandwich compounds with their gas-phase ionization potentials is evident from a linear relationship between the oxidation half- potentials E 1/2 (or sum of Hammett Σσ m values) and the gas-phase ionization potentials.

Photoelectron emission spectroscopy of inorganic cations in aqueous solution

Threshold energies (6.1 < E t ⩽ 8.6 eV) are determined for photoelectron emission by 16 inorganic cations in aqueous solution E t values are correlated with gas-phase ionization potentials, solvation and reorganization free energies, standard reduction potentials and ligand field stabilization energies (five transition metals). Dielectric saturation is shown to drastically lower threshold energies.

Ultraviolet photoelectron spectroscopy and oxidative electrochemistry of 8-hydroxyquinoline and its derivatives

The gas-phase ionization potentials of 8-hydroxyquinoline and several of its alkyl derivatives in the region 8–12 eV are assigned. The energies of the highest occupied molecular orbitals and the half-wave oxidation potentials at a rotating platinum electrode are used to derive empirical values for differential solvation energies for the compounds in acetonitrile and dichloromethane solution.

The oxidation potentials of cis- and trans-1,2-diphenylcyclopropane and cis- and trans-2,3-diphenyloxirane

The oxidation potentials of cis- and trans-1,2-diphenylcyclopropane (1) and cis- and trans-2,3-diphenyloxirane (2) have been determined by cyclic voltammetry, spectroscopically (using an empirical correlation of the long wavelength transition of the charge-transfer complexes with tetracyanoethylene) and by using an empirical correlation based upon the gas phase ionization potentials measured by photoelectron spectroscopy. The values obtained by these three very different techniques agree to within ±0.15 V. The results are interpreted in terms of the initial formation of the phenyl radical cation with the three-membered ring intact. The higher oxidation potentials of cis- and trans-2, relative to those of cis- and trans-1, are attributed to inductive electron withdrawal from the phenyl group by the oxygen of the oxirane ring. The relevance of these results to the photosensitized (electron transfer) behaviour of these compounds is discussed.

ON THE PHOTOIONIZATION ENERGY THRESHOLD OF TRYPTOPHAN IN AQUEOUS SOLUTIONS

Abstract— To investigate the existence and energy position of a photoionization threshold. tryptophan (Trp) has been photoionized in desecrated neutral aqueous or alcoholic solution under monochromatic light of variable frequency, in presence of N2O to scavenge the photoelectron.Present findings and some literature data converge to show the existence of a threshold for the one photon ionization process. This threshold is located at 4.5 ± 0.1 eV and 4.85 ± 0.1 cV for Trp in aqueous and ethanol solutions. respectively, which corresponds to a lowering with respect to the gas phase ionization potential of 3.4 and 3.0 eV.The photoionization quantum yields for Trp is found about 4 times greater at 250 nm than at Λcx= 265 nm, where ϕe‐4M=0.080±0.025. In such spectral range. at most one photoelectron out of 4–5 escaping geminate recombination would lead to Trp photodegradation in acrated solutions.These results also point out that the neutral radical Trp. which has been previously observed for Λcx &gt; 275 nm, i.e. below the ionization threshold energy—would not necessarily derive from Trp + deprotonation or cation‐electron dissociative recombination. Similarly, the opening of the indole ring with formylkynurenine (FK) formation which is observed under aerobic conditions and Λcx &gt;, 280 nm would not imply an electron attachment on O2 but reactions such as Trp +3O2 or Trp*+3O2 or else

Correlation of the photoelectron and electronic spectra of thiochromones and thiochromanones with their electrochemical data

The gas phase ionization potentials, electrochemical redox potentials and spectroscopic properties of a series of thiochroman-4-one and thiochromone derivatives have been studied. A dramatic shift in the energies of the lowest vacant and highest occupied molecular orbitals of the parent thiochromanone as a function of the addition of a double bond and/or oxidation of the sulphur atom was observed. This shift in energy of the molecular orbitals was reflected in their spectroscopic characteristics. The lowest singlet (and triplet) state of compounds 1–3 in solution is π,π* in nature, while that of compounds 4–6 is n,π*. These results are best explained in terms of substituent effects on the energetics of the acetophenone moiety. The change in the nature of the lowest excited state from π,π* (1–3) to n,π* (4–6) should result in quite different types of photochemistry for the two series.A linear free-energy relationship between the singlet and triplet energies and the absolute difference between the oxidation and reduction potentials of the two series was found. These correlations have been utilized to estimate the half-wave oxidation potentials of compounds 3–6. A correlation was found to exist between the gas phase ionization potential and the solution electrochemical oxidation potential.

Photoionization by green light in micellar solution

The anionic micellar system sodium lauryl sulfate was used to produce the photoionization of 3-aminoperylene with green light at lambda = 530 nm. This is some 4.6 eV below the gas phase ionization potential and well into the solar spectrum. The data showed clearly the marked effect of micellar environment on the photoionization yield. The dependence of this yield on the intensity of the laser beam is illustrated. This is the first example of the one-photon ionization of a simple molecule with long wavelength light. The data illustrate possible designs for systems where light energy is converted to ion chemistry which may be later utilized to recover the stored energy. (JSR)

Linear free energy relationships. Triboelectric charging of poly(olefins)

The logarithm of cascade triboelectric charging of substituted polyethylenes and polypropylenes is linearly correlated by inductive substituent constants. The slope is positive as expected for injection of electrons from the metal (Ni) into the lowest unoccupied molecular orbitals of the organic. The logarithm of changing varies linearly with the gas phase ionization potentials of model monomers.

Determination of the absolute energy levels of organic molecules in the gas phase and in condensed media. I. Solution and gas phase ionization energies and electron affinities of substituted pyridine-N-oxides

The basic principle for the determination and interrelation of the absolute energy levels of organic molecules in the gas phase and condensed media are discussed. The electrochemical and gas phase data for a series of substituted pyridine-N-oxides were used to examine the validity of Born’s formula, which approximate the chemical solvation energies of ions. A linear free-energy relationship between the gas phase ionization potentials (I.P.) and the electrochemical half-wave oxidation potentials (Eox1/2) for substituted pyridine-N-oxides was found. This relationship was utilized to predict the ionization potentials of other heterocyclic amine-N-oxides whose I.P.’s have not been measured. The estimated effective ionic radius reff for pyridine-N-oxide derivatives was found to be highly dependent on the nature of the substituent and linearly related to the electrophilic substituent constant σ+. Substituted pyridine-N-oxides have moderately low ionization energies and form stable positive radical cations. Their use as hole traps when immersed in insulating fluid in contact with photoconductors will be discussed.

Photoelectron spectra and molecular properties. 57. Electronic structure and reactivity of ylidic systems. 7. Phosphorus ylides: gas phase ionization potentials and charge distribution

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPhotoelectron spectra and molecular properties. 57. Electronic structure and reactivity of ylidic systems. 7. Phosphorus ylides: gas phase ionization potentials and charge distributionK. A. Ostoja Starzewski, H. Tom Dieck, and H. BockCite this: J. Am. Chem. Soc. 1976, 98, 26, 8486–8494Publication Date (Print):December 1, 1976Publication History Published online1 May 2002Published inissue 1 December 1976https://doi.org/10.1021/ja00442a029RIGHTS & PERMISSIONSArticle Views143Altmetric-Citations62LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (846 KB) Get e-Alerts Get e-Alerts

Experimental determination of ionization potentials of tetraphenylporphine and metallotetraphenylporphines

Gas-phase ionization potentials of tetraphenylporphine and some metallotetraphenylporphines have been determined by the method of photocurrent measurements in nonpolar solvents reported previously [1]. The values obtained range from 5.9 to 6.3 eV, depending on the central metal ion, correlating well with the reported polarographic oxidation potentials. It has been concluded that photoelectron ejection from these complexes in isooctane occurs from the porphyrin π-system in all cases including Co(II) tetraphenylporphine, in which the electron is thought to be removed from the metal in polar solvents.

Organic amino compounds with very low ionization potentials

The gas-phase ionization potentials of some organic amino compounds have been measured by the photo-ionization method. The values obtained lie in the range 5 to 6 eV, probably the lowest of the ionization potentials of organic molecules reported so far.

Carbanion intermediates in the electro-reduction of polycyclic aromatic hydrocarbons

The carbanions formed by monoprotonation of the dianions of some polycyclic aromatic hydrocarbons in formally aprotic solvents can be detected by rapid sweep cyclic voltammetry at a platinum electrode. Those derived from alternant hydrocarbons are oxidized at essentially one potential. Those derived from non-alternant hydrocarbons are oxidized less readily, and at differing potentials. Gas-phase ionization potentials of the anions and electron affinities of the corresponding cations are derived from the solution data.