The interrelation between polarographic half-wave potentials and the energies of electronic excited states

1976 ◽  
Vol 54 (9) ◽  
pp. 1454-1463 ◽  
Author(s):  
Rafik O. Loutfy ◽  
Raouf O. Loutfy
Keyword(s):  
Excited States ◽  
Coulomb Repulsion ◽  
Oxidation Potential ◽  
Absolute Difference ◽  
Linear Free Energy Relationship ◽  
Electronic Excited States ◽  
Reduction Potentials ◽  
Linear Free Energy ◽  
Half Wave ◽  
Experimental Parameters

The polarographic half-wave oxidation and reduction potentials, singlet and triplet energies of a series of (i) monocyclic aza-aromatics, (ii) polycyclic aza-aromatics and their N-oxides, (iii) condensed aromatic hydrocarbons, and (iv) substituted benzene derivatives are reported. The interrelation between the spectroscopic and electrochemical data is developed and discussed in regard to theoretical and experimental parameters. A linear free-energy relationship between the triplet energies and the absolute difference between the oxidation and reduction potentials of the first three series was found. These correlations were utilized to estimate the triplet energies of other molecules in the series, to predict the true half-wave oxidation potential of some heteroaromatic N-oxides and to compute the coulomb repulsion integral. No correlation between ET(π, π*) and (E1/2°x − E1/2R) for substituted benzenes was found. The various reasons for this deviation were discussed.

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

1979 ◽  
Vol 57 (6) ◽  
pp. 638-644 ◽  
Author(s):  
Rafik O. Loutfy ◽  
Ian W. J. Still ◽  
Michael Thompson ◽  
Toong S. Leong
Keyword(s):  
Gas Phase ◽  
Substituent Effects ◽  
Spectroscopic Properties ◽  
Oxidation Potential ◽  
Molecular Orbitals ◽  
Absolute Difference ◽  
Linear Free Energy Relationship ◽  
Redox Potentials ◽  
Reduction Potentials ◽  
Oxidation Potentials

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.

Correlation of π,π* Triplet Energy of some Cyclic α,β-Unsaturated Ketones with Electroreduction Potentials

1972 ◽  
Vol 50 (24) ◽  
pp. 4050-4052 ◽  
Author(s):  
Rafik O. Loutfy ◽  
Raouf O. Loutfy
Keyword(s):  
Free Energy ◽  
Triplet State ◽  
Linear Free Energy Relationship ◽  
Triplet Energy ◽  
Unsaturated Ketones ◽  
Reduction Potentials ◽  
Linear Free Energy ◽  
Half Wave ◽  
Cyclic Enones ◽  
Wave Reduction

The half-wave reduction potentials, E1/2's, of some cyclic enones have been determined in acetonitrile. A linear free-energy relationship was obtained between E1/2 and the lowest π,π* triplet state of the enones studied. This correlation enabled an estimate to be made of the triplet energy of the cyclohexenone, which was found to be ~70 kcal/mol.

Triplet Charge Transfer Complex between Excited Electron Acceptor and Ground State Electron Donor

1972 ◽  
Vol 50 (24) ◽  
pp. 4052-4056 ◽  
Author(s):  
Rafik O. Loutfy ◽  
Raouf O. Loutfy
Keyword(s):  
Free Energy ◽  
Charge Transfer ◽  
Linear Free Energy Relationship ◽  
Quenching Rate ◽  
Linear Free Energy ◽  
Oxidation Potentials ◽  
Half Wave ◽  
Ct Complex ◽  
Quenching Rate Constant ◽  
Ground State Electron

The half-wave reduction and oxidation potentials, E1/2's, of carbonyl compounds and amines, respectively, are used to estimate the location of triplet charge transfer states (CT). A linear free-energy relationship between the calculated CT triplet energies and the corresponding carbonyl molecules triplet energies was obtained. It has also been found that the free energy change (ΔF) for CT complex formation correlate with the triplet carbonyl quenching rate constant kq.

Half-wave potentials of quinone methides in dimethylformamide: Substituent effects

1981 ◽  
Vol 46 (4) ◽  
pp. 861-872 ◽  
Author(s):  
Josef Krupička ◽  
Bohumír Koutek ◽  
Lubomír Musil ◽  
Libuše Pavlíčková ◽  
Milan Souček
Keyword(s):  
Free Energy ◽  
Substituent Effects ◽  
Linear Free Energy Relationship ◽  
Quinone Methides ◽  
Linear Free Energy ◽  
Diffusion Controlled ◽  
Half Wave ◽  
Substituent Constants ◽  
Series Type ◽  
Spin Densities

Half-wave potentials of two series of quinone methides A have been determined in 0.1M tetrabutylammonium perchlorate in dimethylformamide. the first series (type I; 14 compounds) contained fuchsones substituted in positions 2 and 2,6 of the quinonoid ring, the second series (type II and III; 17 compounds) consisted of 2,6-ditert-butylquinone methides, with substituents at the exocyclic C(7) carbon atom. Properties of the first polarographic wave proved that in both series the reaction is one-electron, reversible, diffusion-controlled process. Linear free energy relationship was found between E1/2 and dual substituent constants σI and σR. Statistical analysis of linear free energy relationship for 2- and 2,6-substituted derivatives proved absence of steric factor in transmission of electronic substituent effect. The experimental results were interpreted on the basis of LUMO energies and spin densities, calculated by the HMO method.

Excited State Tracking During the Relaxation of Coordination Compounds

2018 ◽  
Author(s):  
Juan Sanz García ◽  
Martial Boggio-Pasqua ◽  
Ilaria Ciofini ◽  
Marco Campetella
Keyword(s):  
Excited State ◽  
Excited States ◽  
Potential Energy Surfaces ◽  
Photochemical Reactions ◽  
Complex Nature ◽  
Electronic Excited States ◽  
Ruthenium Nitrosyl ◽  
State Tracking ◽  
Energy Surfaces ◽  
Electronic Wavefunction

<div>The ability to locate minima on electronic excited states (ESs) potential energy surfaces (PESs) both in the case of bright and dark states is crucial for a full understanding of photochemical reactions. This task has become a standard practice for small- to medium-sized organic chromophores thanks to the constant developments in the field of computational photochemistry. However, this remains a very challenging effort when it comes to the optimization of ESs of transition metal complexes (TMCs), not only due to the presence of several electronic excited states close in energy, but also due to the complex nature of the excited states involved. In this article, we present a simple yet powerful method to follow an excited state of interest during a structural optimization in the case of TMC, based on the use of a compact hole-particle representation of the electronic transition, namely the natural transition orbitals (NTOs). State tracking using NTOs is unambiguously accomplished by computing the mono-electronic wavefunction overlap between consecutive steps of the optimization. Here, we demonstrate that this simple but robust procedure works not only in the case of the cytosine but also in the case of the ES optimization of a ruthenium-nitrosyl complex which is very problematic with standard approaches.</div>

Synthesis and characterization of a series of 1-methyl-4-[2-aryl-1-diazenyl]piperazines and a series of ethyl 4-[2-aryl-1-diazenyl]-1-piperazinecarboxylates

2004 ◽  
Vol 82 (8) ◽  
pp. 1294-1303 ◽  
Author(s):  
Vanessa Renée Little ◽  
Keith Vaughan
Keyword(s):  
Free Energy ◽  
Chemical Shifts ◽  
Linear Free Energy Relationship ◽  
Piperazine Ring ◽  
Linear Free Energy ◽  
In Series ◽  
Methylene Groups ◽  
Diazonium Coupling ◽  
The Difference

1-Methylpiperazine was coupled with a series of diazonium salts to afford the 1-methyl-4-[2-aryl-1-diazenyl]piperazines (2), a new series of triazenes, which have been characterized by 1H and 13C NMR spectroscopy, IR spectroscopy, and elemental analysis. Assignment of the chemical shifts to specific protons and carbons in the piperazine ring was facilitated by comparison with the chemical shifts in the model compounds piperazine and 1-methylpiperazine and by a HETCOR experiment with the p-tolyl derivative (2i). A DEPT experiment with 1-methylpiperazine (6) was necessary to distinguish the methyl and methylene groups in 6, and a HETCOR spectrum of 6 enabled the correlation of proton and carbon chemical shifts. Line broadening of the signals from the ring methylene protons is attributed to restricted rotation around the N2-N3 bond of the triazene moiety in 2. The second series of triazenes, the ethyl 4-[2-phenyl-1-diazenyl]-1-piperazinecarboxylates (3), have been prepared by similar diazonium coupling to ethyl 1-piperazinecarboxylate and were similarly characterized. The chemical shifts of the piperazine ring protons are much closer together in series 3 than in series 2, resulting in distortion of the multiplets for these methylenes. It was noticed that the difference between these chemical shifts in 3 exhibited a linear free energy relationship with the Hammett substituent constants for the substituents in the aryl ring. Key words: triazene, piperazine, diazonium coupling, NMR, HETCOR, linear free energy relationship.

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