Perylene cation-radical

Synthesis of Radical Cation Perchlorates and Subsequent Coupling with NucleophilesT Syntheses of the radical cation perchlorates of BP and 6-methylBP (12) were accomplished by the method reported earlier for the preparation of the perylene radical cation (13,14). More recently we have also synthesized the radical cation perchlorate of 6-fluoroBP (15). Oxidation of the PAH with iodine in benzene in the presence of AgClO. instantaneously produces a black precipitate containing the radical cation perchlorate adsorbed on Agl with... 

Figure 4 EPR spectra of perylene radical cation on (a) HY zeolite ...

Perylene and tetracene both undergo photo-induced electron-transfer reactions with pyromellitic anhydride (Levin, 1976). If a mixture of perylene and tetracene is used, and the light absorbed by the perylene, the perylene radical cation will be formed which because of the relative oxidation potentials will react with tetracene to give the tetracene radical ion. Thus the photogenerated perylene radical cation has undergone a redox reaction with tetracene. In effect, the perylene has acted as a sensitiser for the production of the tetracene radical cation. This type of sensitisation has been used to effect a number of reactions. 

Liq Cryst 62 181 (1980) (b) W. Briitting and W. Riess Peierls Instability and Charge-Density-Wave Transport in Fluoranthene and Perylene Radical-Cation Salts Acta Phys. Pol. A 87 785 (1995). 

Tokmachev AM et al (2010) Fluorescence of the perylene radical cation and an inaccessible D-O/D-1 conical intersection an MMVB, RASSCF, and TD-DFT computational study. J Chtan Phys 132 9... 

One of the most commonly studied systems involves the adsorption of polynuclear aromatic compounds on amorphous or certain crystalline silica-alumina catalysts. The aromatic compounds such as anthracene, perylene, and naphthalene are characterized by low ionization potentials, and upon adsorption they form paramagnetic species which are generally attributed to the appropriate cation radical (69, 70). An analysis of the well-resolved spectrum of perylene on silica-alumina shows that the proton hyperfine coupling constants are shifted by about four percent from the corresponding values obtained when the radical cation is prepared in H2SO4 (71). The linewidth and symmetry require that the motion is appreciable and that the correlation times are comparable to those found in solution. 

It is also possible to form radical cations and radical anions on the same alumina or silica-alumina surface (88). One of the more interesting observations was that a marked enhancement of the radical anion spectrum for trinitrobenzene results when perylene is adsorbed on an alumina surface, and similarly the radical cation signal is reenforced by adsorption of trinitrobenzene. The linewidths of the spectra confirm that the radical ions are separated by a distance greater than 10 A. This means that the electron must be transfered through the lattice or that the ions separate after the transfer step, which seems unlikely. Oxygen was still required for the formation of the radical cation. 

This list includes BP, 7,12-dimethylbenz[a]anthracene, 3-methylchol-anthrene, dibenzo[a,i]pyrene and dibenzo[a,h]pyrene. These PAH can be activated both by one-electron oxidation and/or monooxygenation. There are a few PAH with low IP which are inactive (Table I), such as perylene, or weakly active, such as anthanthrene. This indicates that low IP is a necessary, but not sufficient factor for determining carcinogenic activity by one-electron oxidation. These inactive or weakly active PAH have the highest density of positive charge delocalized over several aromatic carbon atoms in their radical cations, whereas the active PAH with low IP have charge mainly localized on one or a few carbon atoms in their radical cations. 

It is now well established that when a surface presents electron donor or electron acceptor sites, it is possible to ionize molecules of relatively high electron affinity (> 2 eV) or low ionization potential values, resulting in paramagnetic radical ions. For instance anthracene and perylene are easily positively ionized on alumina (7 ) (IP = 7.2 and 6.8 eV respectively). The adsorption at room temperature of benzenic solution of perylene, anthracene and napthalene on H-ZSM-5 and H-ZSM-11 samples heated up to 800°C prior to adsorption did not give rise to the formation of the corresponding radical cation. For samples outgassed at high... 

Figures 5a, 5c, and 5e demonstrate the effect on the TNB spectrum of an increase in the concentration of adsorbed perylene cation radicals (Figure 5c, 4 X 1018 cation radicals per gram Figure 5e, 1 X 1019). The outer features of the anion-radical spectrum become much less evident as the perylene radical concentration is increased. This effect is more pronounced at low temperatures (Figures 5d and 5f). Although the spectrum for TNB adsorbed alone on decationated Y is less well resolved at the lower temperature (Figure 5b), the outer features are still clearly discernible with this system saturation broadening accounts for the loss of resolution.

The photooxidation of p-phenylenediamine to the Wurster s Blue radical cation apparently proceeds by photoionization of the excited triplet state of the neutral molecule,219 and it has been suggested that the delayed fluorescence of perylene may be partly due to photoionization of its triplet state and slow subsequent recombination of... 

Figure 1 Proposed mechanism for the generation of the radical anion and radical cation of perylene diimide and self-annihilation of the two to yield the triplet excited state.

Radical cations act both as electrophiles and one-electron oxidants toward nucleophiles (Eberson, 1975 Bard et al, 1976 Eberson et al., 1978a,b Evans and Blount, 1978) as shown in (6), and it is therefore important to find out which factors govern the competitition between these reaction modes. Evans and Blount (1978) measured rate constants and products for a number of [9,10-diphenylanthracene)+ /nucleophile reactions and found that iodide, rhodanide, bromide and cyanide undergo oxidation, whereas nucleophiles that are more difficult to oxidize form a C—Nu bond directly. Entry no. 13 of Table 15 shows non-bonded electron transfer to be feasible for these ions, and the reactions of [perylene]+ with iodide, rhodanide and bromide (entry no. 14) presumably can be classified in the same way. The reaction with chloride ion... 

Eberson and co-workers have recently discussed the probability that the interaction of ion-radicals with nucleophiles and electrophiles is subject to orbital symmetry constraints.31,32 This follows the observation that with perylene the cation-radical (18) the preferred course of reaction with halide ions is electron transfer rather than nucleophilic addition, whereas with the phenothiazine cation-radical (19) nucleophilic attack by Cl" and Br occurs. 

In the twentieth century, Kehrmann applied this reagent for the one- and two-electron oxidation of phenothiazine and characterized semiquinoid and holoquinoid species by UV/VIS spectroscopy (Fig. 4) [44,45], In the 1950s colored solutions of aromatic hydrocarbons (perylene, anthracene, etc.) in sulfuric add were found to be paramagnetic [46] and, shortly thereafter, their radical cations were postulated based on optical [47] and ESR spectroscopic data [48]. The detailed reaction mechanisms of these oxidations are still in question molecular oxygen may well be a necessary ingredient... 

Various compounds were shown to sensitize the photochemical decomposition of pyridinium salts. Photolysis of pyridinium salts in the presence of sensitizers such as anthracene, perylene and phenothiazine proceeds by an electron transfer from the excited state sensitizer to the pyridinium salt. Thus, a sensitizer radical cation and pyridinyl radical are formed as shown for the case of anthracene in Scheme 15. The latter rapidly decomposes to give pyridine and an ethoxy radical. Evidence for the proposed mechanism was obtained by observation of the absorption spectra of relevant radical cations upon laser flash photolysis of methylene chloride solutions containing sensitizers and pyridinium salt [64]. Moreover, estimates of the free energy change by the Rehm-Weller equation [65] give highly favorable values for anthracene, perylene, phenothiazine and thioxanthone sensitized systems, whilst benzophenone and acetophenone seemed not to be suitable sensitizers (Table 5). The failure of the polymerization experiments sensitized by benzophenone and acetophenone in the absence of a hydrogen donor is consistent with the proposed electron transfer mechanism. 

For example, Vincow and coworkers (205) have prepared radical cations of benzene, hexamethylbenzene, perylene, naphthalene, etc., by photoionization of the molecules in a rigid glass, while Hulme and Symons (206) have... 

When benzenoid organic hydrocarbons such as naphthalene (60), fluoranthene (116), perylene (112) or pyrene (117) are subjected to electrochemical oxidation at a platinum electrode in the presence of supporting electrolytes in solvents such as methylene chloride or acetonitrile, one frequently observes the deposition of crystals on the electrode [310]. When denoting the substrate as A and the supporting electrolyte as MX there are two nucleophilic species competing for the radical cation A", i.e., the neutral molecule A and the closed-shell counteranion X , and it is, indeed, the equilibrium constant of the... 

In the above radical-cation salts, the crystal contains partially oxidized donors, while the electroneutrality is achieved by the presence of closed shell anions. The structural requirements necessary for electrical conductivity in solid salts can also be met upon mixing of donors and acceptors in the resulting charge-transfer (CT) complexes both the donor and acceptor exist in a partially oxidized and reduced state, respectively. Famous examples are the conducting CT complexes formed upon mixing of perylene (112) [323. 324] and iodine or of tetrathiafulvalene (TTF, 119) as donor and 7,7,8,8-tetracyanoquinodimethane (TCNQ, 120) as acceptor [325-327] the crucial structural finding for the... 

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