Showing papers on "Radical ion published in 1987"

Organic Electrochemistry in the Solid State‐Overoxidation of Polypyrrole

Abstract: Anodic overoxidation of polypyrrole in the presence of nucleophiles such as H2O, OH−, CH3OH, CH3O−, Br− and CN− has been studied in detail. At potentials up to 2.1 V (vs. SCE), irreversible anodic peaks are observed with 200 nm layers on Pt. In most of the cases, a total of z = 4 – 6 F/mol monomer unit initially oxidized in the reversible potential region to the radical cation has been evaluated. Only every third ring is involved by this way. Characteristic products in aqueous systems are pyrrolinones (with a keto group in 3-position), z = 4, and the product of further hydroxylation in 4-position (z = 6). In the presence of the other nucleophiles, corresponding substitution products seem to be generated. The central reactive intermediate seems to be the dication. Pronounced deviations from this scheme, which is confirmed by IRRAS results, seem to proceed in the presence of strong nucleophiles as OH−, which add initially to the radical cation, and upon strong polarization, which may lead to an attack of the other rings and/or polymer destruction. Practical implications are due to polymer modification and battery material optimization.

Return Electron Transfer within Geminate Radical Ion Pairs: Observation of the Marcus Inverted Region

Abstract: In recent years the physical and chemical properties of photoinduced electron-transfer reactions have been extensively studied with particular emphasis on maximizing the efficiency of charge separation. However, energy-wasting return electron transfer, especially within the primary geminate radical ion pair for singlet-state reactions, often results in low quantum yields for free-ion formation. Detailed studies of the mechanisms and kinetics of product formation for several photosensitized electron-transfer reactions suggest that a relationship exists between the thermodynamics and the kinetics of the return electron transfer process. In this work the authors summarize the results of laser flash photolysis studies which were specifically designed to study this relationship. The results provide a clear example of the Marcus inverted region in these processes. Experiments were performed in degassed acetonitrile at room temperature using 9,10-dicyanoanthracene (DCA) and 2,6,9,10-tetracyanoanthracene (TCA) as the excited-state sensitizers and electron acceptors and naphthalene derivatives, diphenylacetylene, and biphenyl as the electron donors. Absolute quantum yields for formation of free radical ion (Theta/sub sep/) were determined by using conventional laser flash photolysis.

Photoreactions of biacetyl, benzophenone, and benzil with electron-rich alkenes

Abstract: The rate constants (k/sub q/) for fluorescence and phosphorescence quenching of biacetyl by electron-rich alkenes were measured in acetonitrile solution at room temperature. A weak dependence of log k/sub q/ on the free enthalpy change (..delta..G/sub 2/) for electron transfer in the triplet state in the range 0 ..delta..G/sub 2/ > -0.70 eV points to electron-transfer processes in singlet and triplet states. Quenching of the phosphorescence and the T-T absorption of benzophenone reveals larger (smaller) k/sub q/ values in the endergonic (exergonic) region, as compared to the Rehm-Weller correlation. The slope of the plot of log k/sub q/ vs. ..delta..G/sub 2/ is similar to that of biacetyl in the endergonic region. The latter indicates that electron transfer in this instance is not the primary step. For benzil the plot of log k/sub q/ vs ..delta..G/sub 2/ resembles more closely that of biacetyl, pointing to a similar mechanism. In the exergonic region electron transfer is observed for benzil (major process) and benzophenone (minor process) by detection of the radical anion with use of nanosecond laser flash photolysis. The yield andmore » half-life of the radical anion depend on the nature of the electron donor and the ketone, the solvent polarity, and the additives (e.g., LiClO/sub 4/, special salt effect). The solvent effect on the photoproducts (oxetanes) is correlated with the free enthalpies of radical ion pair formation.« less

Photoelectron transfer from tris(2,2'-bipyridine)ruthenium(II) to methylviologen in zeolite cages: a resonance Raman spectroscopic study

Abstract: Resonance Raman spectra and photoelectron transfer by visible light in the system Ru(bpy)/sub 3//sup 2 +/-MV/sup 2 +/-Na-zeolite Y are examines. The Ru(bpy)/sub 3//sup 2 +/ molecule is trapped in the dehydrated zeolite Y supercages. Upon photoexcitation of this molecule, MV/sup .+/ radical cations are formed in neighboring cages. The radical cation is stable on the hour time scale and decays by back electron transfer to Ru(bpy)/sub 3//sup 3 +/. The resonance Raman spectrum of the radical cation shows evidence of interactions with the zeolite framework.

Free radicals and metal ions in health and disease

Abstract: an atom of hydrogen (H') to form water. This reaction removes the OH', but leaves behind in the membrane another type of radical species, a carbon-centred radical. This can undergo various other reactions, including a reaction with molecular oxygen to form a third type of radical species, the peroxy radical. Peroxy radicals can react with another membrane fatty acid side-chain (Fig. I), converting themselves into lipid peroxides. This is achieved by further H' abstraction, forming another carbon-centred radical that can react with more 0, and carry on the reaction. Hence OH' attack on a membrane system can start off a radical chain reaction known as lipid peroxidation (Fig. I). A lipid peroxide is obviously more polar than anything that should be present in the hydrophobic interior of a biological membrane. Lipid peroxidation diminishes membrane fluidity, increases non-specific permeability to ions (e.g. Ca2+) and may inactivate membrane-bound enzymes. Further, in the presence of various kinds of https://www.cambridge.org/core/terms. https://doi.org/10.1079/PNS19870004 Downloaded from https://www.cambridge.org/core. IP address: 54.70.40.11, on 07 Mar 2019 at 09:17:04, subject to the Cambridge Core terms of use, available at

Spin-crossover cobalt(III) complexes: steric and electronic control of spin state

Abstract: The series of octahedral Co(III) spin-crossover complexes (III) is synthesized from the corresponding Co(II) complexes (Ia) by oxidation with the radical cation of (II).

Simultaneous capture of two distinct radical ion intermediates generated from the EDA complexes of three-membered compounds with TCNE by photoexcitation and in the dark

Abstract: Irradiation of the electron donor-acceptor (EDA) complexes of 2,2-diaryl-1-methylenecyclopropanes, 1,1,2,2-tetraarylcyclopropanes, 2,3-diaryloxiranes, or 2,3-diarylaziridines with tetracyanoethylene (TCNE) under aerated conditions involved oxygenation and/or the (3 + 2) cycloaddition with TCNE. The same oxygenation took place in the dark when the EDA complexes of 2,2-diaryl-1-methylenecyclopropanes or 1,1,2,2-tetraarylcyclopropanes with TCNE were simply stirred in oxygen-saturated solvents. Oxygenation occurred much more efficiently as the solvent polarity and the electron-donative nature of donor substrates increased. 1,2,4,5-Tetramethoxybenzene (TMB) used as a quencher efficiently suppressed oxygenation but not the (3 + 2) cycloaddition at all. Oxygenation occurs through the solvent-separated radical cations diffused from the photogenerated geminate radical ion pairs, whereas the cage coupling of the radical ion pairs involves the (3 + 2) cycloaddition with TCNE.

The SO4(.-)-induced chain reaction of 1,3-dimethyluracil with peroxodisulphate

Abstract: The sulphate radical SO4(.-) reacts with 1,3-dimethyluracil (1,3-DMU) (k = 5 X 10(9) dm3 mol-1 s-1) thereby forming with greater than or equal to 90 per cent yield the 1,3-DMU C(5)-OH adduct radical 4 as evidenced by its absorption spectrum and its reactivity toward tetranitromethane. Pulse-conductometric experiments have shown that a 1,3-DMU-SO4(.-) aduct 3 as well as the 1,3-DMU radical cation 1, if formed, must be very short-lived (t1/2 less than or equal to 1 microsecond). The 1,3-DMU C(5)-OH adduct 4 reacts slowly with peroxodisulphate (k = 2.1 X 10(5) dm3 mol-1 s-1). It is suggested that the observed new species is the 1,3-DMU-5-OH-6-SO4(.-) radical 7. At low dose rates a chain reaction is observed. The product of this chain reaction is the cis-5,6-dihydro-5,6-dihydroxy-1,3-dimethyluracil 2. At a dose rate of 2.8 X 10(-3) Gys-1 a G value of approximately 200 was observed ([1,3-DMU] = 5 X 10(-3) mol dm-3; [S2O8(2-)] = 10(-2) mol dm-3; [t-butanol] = 10(-2) mol dm-3). The peculiarities of this chain reaction (strong effect of [1,3-DMU], smaller effect of [S2O(2-)8]) is explained by 7 being an important chain carrier. It is proposed that 7 reacts with 1,3-DMU by electron transfer, albeit more slowly (k approximately 1.2 X 10(4) dm3 mol-1 s-1) than does SO4(.-). The resulting sulphate 6 is considered to hydrolyse into 2 and sulphuric acid which is formed in amounts equivalent to those of 2. Computer simulations provide support for the proposed mechanism. The results of some SCF calculations on the electron distribution in the radical cations derived from uracil and 1-methyluracil are also presented.

Linear alkane radical cations prepared in synthetic zeolites by irradiation at 4 K: ESR evidence for ion-molecule reaction to form 1-alkyl radicals

Abstract: A new method is explored for preparing radical cations of alkanes in the system other than halogenated and neon matrices. The radical cations are produced from n-C/sub 6/H/sub 14/ and n-C/sub 8/H/sub 18/ adsorbed in synthetic zeolite (ZSM-5) by X-irradiation at 4 K. The ESR spectra show that the cations exhibit the planar extended structure without showing coexistence of the gauche conformer. With increasing the concentration of alkanes, the parent molecules are increasingly adsorbed as a dimer, from which the 1-alkyl radical is preferentially formed during irradiation at 4 K. This indicates that the n-alkane radical cation undergoes prompt deprotonation via the ion-molecular reaction when a neighboring alkane molecule exists as a proton acceptor in the adsorbed site. The formation of the 1-alkyl radical is consistent with the high unpaired electron density in the in-plane C-H bonds at the chain end of the radical cations. These results are closely related to their previous finding of the selective formation of the 1-alkyl radicals in the 4 K radiolysis of crystalline neat linear alkanes.

Kinetics of pyrrole polymerisation in aqueous iron chloride solution

Abstract: The chemical oxidation of pyrrole by iron(III) chloride in aqueous solutions of methylcellulose has been investigated. The kinetics of the reaction were studied by following the absorption of the soluble (colloidal), oxidised poly(pyrrole) product at 800 nm. In the pH interval 0–0.5 the reaction was first-order in FeIII and pyrrole concetrations and zero-order in proton concentration. For pH > 1.3, the kinetic curves exhibited behaviour characteristic of autocatalytic reactions. A mechanism is proposed in which the rate-limiting step is the oxidation of pyrrole to a radical cation by an outer-sphere activated-complex mechanism. The observed pH dependence on the rate is attributed to the hydrolysis equilibrium for FeIII in solution, in which lower pH decreases the concentration of OH–, which can hinder pyrrole from approaching the oxidant. The observed autocatalytic behaviour at higher pH is caused by the fact that the polymerisation produces protons. A brief comparison with oxidation by ammonium persulphate is given.

The role of peroxidases, radical cations and oxygen in the degradation of lignin

Abstract: Ligninase is an extracellular peroxidase produced by several species of white-rot fungi. It is able to oxidize methoxylated substrates to radical cation intermediates that can undergo C-H or C-C bond cleavage, thereby providing the basis for the oxidation of veratryl alcohol or degradation of lignin model compounds respectively. In some cases, the radical cation intermediate can act as an oxidant, accepting an electron from a suitable donor. It can thus function as a mediator, causing oxidation in a polymer not immediately accessible to the enzyme. This could be important in the degradation of natural lignocellulose substrates. However, the removal of a single electron by a mediator would leave a radical in the polymer. We propose that oxygen will bind to this radical to generate active oxygen species. This provides a potential mechanism for the auto-oxidation of lignin at a distance from the enzyme. A scheme is presented to account for the observation that ligninase can open the ring of veratryl alcohol.

New Aspects in the Free-Radical Chemistry of Pyrimidine Nucleobases

Abstract: i) It has been known for some time that OH radicals and H atoms react with the pyrimidines by adding to the C(5)-C(6) double bond, but only the u.v.-spectra of the sum of these radicals have been reported so far. It will be shown how to arrive at the individual spectra of the C(5) and the C(6) adduct radicals. ii) alpha-Hydroxyalkyl radicals are known to inactivate biologically active DNA. In contrast to the electrophilic radicals H and OH they are nucleophilic and the hydroxymethyl radicals add exclusively at the C(6) position of 1,3-dimethyluracil (k approximately 10(4) dm3 mol-1 s-1). In the corresponding thymine derivative this reaction also occurs, but one third of the hydroxymethyl radicals abstract an H-atom from the C(5)-methyl group thereby forming an allylic radical. In the course of these reactions pyrimidines with an exocyclic double bond are formed. These products react much more rapidly with hydroxymethyl radicals than the starting material leading to highly hydroxymethylated material at very low doses. iii) The direct effect of ionizing radiation which would produce a pyrimidine base radical cation can be mimicked by reacting the pyrimidine with SO4-, a very good electron acceptor. In water, the radical cation of 1,3-dimethyluracil is rapidly (t1/2 less than 2 microseconds) converted into the C(5) OH adduct radical. In the presence of peroxodisulphate a chain reaction sets in which leads to the cis-glycol.

Specific Deprotonation Reactions of the Pyrimidine Radical Cation Resulting from the Menadione Mediated Photosensitization of 2′-Deoxycytidine

Abstract: Menadione(2-methyl-1, 4-naphthoquinone) was shown to sensitize 2′-deoxycytidine to near ultraviolet light according to two main mechanisms. Reaction of a water molecule with the initially photo-induced pyrimidine radical cation and subsequent addition of molecular oxygen leads to the preponderant formation of the four cis and trans diastereoisomers of 5,6-dihydroxy-5,6-dihydro-2′-deoxyuridine. Pyrimidine ring opening and rearrangement products are also generated through the intermediate 6-hydroxy-5,6-dihydro-2′-deoxyurid-5-yl radical. The competitive deprotonation reaction of the radical cation is likely to involve two sites. Loss of an amino group proton is the likely initial event to explain the formation of 2′-deoxyuridine which is resistant to further photooxidation. The second deprotonation reaction involves the osidic carbon C(1′). The resulting radical will further react with oxygen leading to the release of free cytosine with concomitant formation of 2-deoxy-D-ribono-1,4-lactone. This reaction whi...

ESR studies of the thietane and thiirane radical cations in freon matrixes. Evidence for ethylene molecule extrusion from a .sigma.* thiirane dimer radical cation [C2H4S-SC2H4.bul.+]

Abstract: ESR spectroscopy has been used to study the structures and reactions of the radical cations produced from the three- and four-membered sulfur-containing ring compounds, thiirane and thietane, the radical cations being generated by ..gamma.. irradiation of dilute solutions of the parent compounds in Freon matrices at 77 K. With use of CFCl/sub 3/ as the matrix, the monomer radical cations have been identified and characterized as having /sup 2/B/sub 1/ ring-closed structures with the unpaired electron localized on the sulfur atom. The hyperfine coupling to the four equivalent ..beta..-hydrogens in the thietane cation (31.1 G) is normal, but the corresponding value for the thiirane cation (16.1 G) is lower by almost a factor of 2, suggesting that hyperconjugation to methylene groups is much reduced in three-membered rings. In the more mobile CFCl/sub 2/CF/sub 2/Cl and CF/sub 3/CCl/sub 3/ matrices, dimer radical cations of thiirane and thietane are produced by the combination of a monomer radical cation with a neutral molecule at low temperatures (< 100 K). ESR studies show that these dimer species are centrosymmetric, the binding between the molecules resulting from the formation of a 3-electron sigma/sup 2/sigma*/sup 1/ S-S bond. Both of the dimer cations are unstable abovemore » 105 K in the CFCl/sub 2/CF/sub 2/Cl matrix, the thietane dimer radical cation decomposing to give the 2-thietanyl radical as a result of hydrogen atom or proton transfer, whereas the thiirane dimer radical cation undergoes a novel reaction involving the extrusion of an ethylene molecule.« less

Resonance Raman spectra of p-benzosemiquinone radical and hydroquinone radical cation

Abstract: The time-resolved resonance Raman spectrum of the p-benzosemiquinone radical (HOC/sub 6/H/sub 4/O), excited at 415 nm and observed on the microsecond time scale in the pulse radiolysis of moderately acidic solutions of hydroquinone (pH 2-4), is reported. The nu/sub 7a/ CO stretching mode appears prominently in the spectrum at 1511 cm/sup -1/, showing that the CO bond is very similar to that in phenoxyl where this vibration is observed at 1505 cm/sup -1/. Strongly resonance enhanced bands are also observed at 1613 and 1162 cm/sup -1/ and are assigned respectively to the nu/sub 8a/ ring stretching and nu/sub 9a/ CH bending modes. The strong enhancement of these latter vibrations, which are very much weaker in the corresponding spectrum of the phenoxyl radical, and the similarity of the ring stretching frequency (nu/sub 8a/) to that in p-benzosemiquinone radical anion (1620 cm/sup -1/) indicate that there is a strong interaction of the OH p(..pi..) electron pair with the phenoxyl radical's ..pi..-electron system. The coefficient for the acid-catalyzed dehydroxylation of the OH adduct of hydroquinone is estimated from the pH and time dependences of the Raman signals of the semiquinone to be 5.4 x 10/sup 8/ M/sup -1/ s/sup -1/. In strongly acidicmore » solutions (e.g., approx. 2.3 M H/sub 2/SO/sub 4/) a second transient species, identified as the hydroquinone radical cation, is observed. The vibrational features of this radical are qualitatively similar to those for p-benzosemiquinone radical anion with the nu/sub 8a/ ring stretching mode very strongly resonance enhanced and observed at 1644 cm/sup -1/. The nu/sub 7a/ CO stretching mode is observed at 1426 cm/sup -1/ but is very much weaker than in the corresponding spectrum of the radical anion.« less

Photochemical dehydrofragmentation reactions: importance of donor and acceptor structure in determination of reactivity in radical ion pairs formed in electron-transfer photoreactions

Abstract: Photoinduced electron-transfer reactions are the subject of considerable interest due both to the versatility of net chemical reactions which can be achieved as well as to the variety of intermediates and mechanistic complexities encountered in their study. For initially neutral donors and acceptors quenching of excited singlet states is frequently dominated by formation of a geminate ion pair, A/sup -//D/sup +/, which can subsequently decay by back electron transfer or, in moderately polar to polar solvents, by cage escape to form free ions. In nonpolar solvents the back electron transfer process acts as an effective clock to limit the lifetime for reaction of the geminate pair to the ns time; consequently only relatively rapid reactions can occur efficiently from the geminate pair and these frequently involve participation of the solvent or other reagents present in high concentration. The authors have previously reported the chemically clean and moderately efficient C-C bond photofragmentation reactions of ..beta..-amino-alcohols initiated by electron transfer to excited acceptors. They report here a mechanistic study where this reaction is restricted to the geminate pair and which emphasizes the complimentary roles of reduced acceptor and oxidized donor in facilitating chemical reaction in competition with fast back electron transfer. Amore » key result is that rapid fragmentation is coincident with acceptor radical anion induced deprotonation of the donor cation radical and thus strongly dependent on acceptor structure.« less

Time resolved resonance Raman spectra of anilino radical and aniline radical cation

Abstract: We report, in this paper, submicrosecond time resolved resonance Raman spectra of anilino radical and its radical cation as observed in pulse radiolytic studies of the oxidation of aniline in aqueous solution. By excitation in resonance with the broad and weak electronic transition of anilino radical at 400 nm (e∼1250 M−1 cm−1) we have observed, for the first time, the vibrational features of this radical. The Wilson ν8a ring stretching mode at 1560 cm−1 is most strongly resonance enhanced. The ν7a CN stretching band at 1505 cm−1, which is shifted to higher frequency by 231 cm−1 with respect to aniline, is also prominent. The frequency of this latter mode indicates that the CN bond in the radical has considerable double bond character. The Raman spectrum of aniline radical cation, excited in resonance with the ∼425 nm electronic absorption (e∼4000 M−1 cm−1), shows features which are similar to phenoxyl radical. Most of the observed frequencies of this radical in solution are in good agreement with vibrati...

ESR studies on the radical cation mechanism of the ring opening of cyclopropylamines

Abstract: Cyclopropylamine radical cations have been implicated in the mechanism of inactivation of monoamine oxidase and cytochrome P-450 by cyclopropylamines. The key step in the proposed mechanism is illustrated for the parent compound in Scheme I and consists of the ring opening of the aminium radical cation 1 to the carbon-centered radical 2 which subsequently attacks the active site of the enzyme. Here they present ESR evidence for this ring-opening reaction and report that 2 is not converted to the nitrogen-centered radical 3 whereas the corresponding reaction for the neutral radical proceeds to completion at similar temperatures. These results provide a firm basis for the radical cation mechanism of enzyme inactivation, in keeping with the structural evidence that the inactivator is bound to the enzyme through carbon rather than nitrogen.

MENADIONE SENSITIZED PHOTOOXIDATION OF NUCLEIC ACID and PROTEIN CONSTITUENTS. AN ESR and SPIN-TRAPPING STUDY

Abstract: The menadione photosensitized reactions of nucleic acid and protein constituents were studied by ESR and spin trapping. Thymine, thymidine, cytosine, 2′-deoxycytidine,5′-dCMP, uracil and several N-acetyl amino acids and dipeptides were investigated. Photolysis at 335 nm was carried out in air-saturated or Ar saturated DMSO : H2O (1 : 1, vol/vol) containing 10 3M menadione and 10-2M 2-methyl-2-nitrosopropane as the spin trap. The observed spin adducts were explained in terms of electron transfer from the substrate to the excited triplet state of menadione to form the radical cation of the substrate and the anion radical of menadione which was also detected by ESR.

Reinvestigation of the aluminum hydride (AlH+ and AlD+) cation radicals by ESR in argon matrices at 4 K: Generation by reactive laser sputtering

Abstract: The ESR spectra previously assigned to the AlH+ radical ion (X 2Σ) [J. Chem. Phys. 71, 3991 (1979)] actually belong to the divalent neutral aluminum radical AlHOH whose charge distribution and electronic structure can be described as AlH+OH− with 90% of the unpaired electron on the AlH+ part of the molecule. Reactive laser sputtering and photoionization of AlH(g) were used to generate the AlH+ and AlD+ cation radicals, whose ESR spectra have been observed for the first time. A detailed analysis of the ESR results for argon matrices at 4 K reveal unusually large Al hyperfine interaction (hfi) with Aiso and Adip values of 1586(2) and 49(1) MHz, respectively. The H hfi is essentially isotropic with Aiso=442(2) MHz. The observed nuclear hyperfine A tensors for Al and H show excellent agreement with ab initio CI theoretical calculations. The results for AlH+ are compared with the isoelectronic neutral radical MgH, and the similar AlF+ cation radical. The Al hfi is slightly larger in AlD+ relative to AlH+. This...

Arene-iminium salt electron-transfer photochemistry. Mechanistically interesting photoaddition processes

Abstract: Studies of the electron-transfer photochemistry of arene-iminium salt systems have been explored. Fluorescence quenching investigations have demonstrated that a series of arenes including substituted toluenes and benzenes quench the fluorescence of a variety of 2-aryl-1-pyrrolinium perchlorates. Quenching rate constants in these cases correlate with the ..delta..G/sub SET/ values as expected for quenching by reversible electron-transfer pathways. In addition, nonconjugated iminium salts quench the fluorescence of a host of arenes with k/sub q/ values which parallel those predicted on the basis of electron-transfer free energy calculations. Photoaddition reactions of toluene, benzyltrimethylsilane, benzyltrimethylstannane, and 2-aryl-1-pyrrolinium salts have been explored. Likewise, electron-transfer-induced, excited-state reactions of toluene and benzyltrimethylsilane with 1,2-dimethyl-1-pyrrolinium perchlorate have been investigated. The results of these photoreactions have been interpreted in terms of steric, electrofugal group, and solvent effects upon the rates of competitive pathways available to initially formed radical cation pair intermediates. Finally, the photochemistry of benzyltrimethylstannane is described.

Triplet (T1) state and radical cation resonance Raman spectroscopy of N,N,N′,N′‐tetramethyl‐ and N,N,N′,N′‐tetraethyl‐p‐phenylenediamines

Abstract: The time‐resolved resonance Raman spectra of the first triplet state and the cw resonance Raman spectra of the radical cation are reported for various isotopic derivatives of the N,N,N′,N′‐tetramethyl‐p‐phenylenediamine (TMPD) and of the N,N,N′,N′‐tetraethyl‐p‐phenylenediamine (TEPD). Vibrational assignments and structural implications are discussed. The radical cation spectra are consistent with a semiquinoidal conformation of the ionized species. They are characterized by a significant frequency increase of the in‐phase ν(N–ring) mode with respect to the ground state spectra (Δν≥120 cm−1) and by the high resonance enhancement of various bands assigned to vibrations of the N(alkyl)2 groups, resulting from couplings of these vibrations with modes of the π chromophore. The triplet spectra display almost only bands due to vibrations of the N(alkyl)2 groups, implying that similar couplings take place in the T1 state. Two signals characterize the N–ring–N framework: one is assigned to the Wilson ring mode 9a ...

Photodissociation spectroscopy of the negative ion dimer of toluquinone

Abstract: The photodissociation spectrum of the negative ion dimer of toluquinone has been determined in an ion cyclotron resonance spectrometer. A charge resonance transition at 1.9 eV, which displays individual vibronic transitions at high resolution, has been identified. The bond dissociation energy and electron affinity of the dimer were determined from the data. The charge resonance transition was fit to a single-oscillator theoretical model and details of the electronic structure were extracted. The fit to the data indicates that the odd electron in the radical ion dimer is strongly localized.