Perylene radical anion

Other selected examples include tris(tetramethylethylene diamine-sodium)-9,9-dianthryl 143,154 alkali metal salts of 9,10-bis(diisopropylsilyl)anthracene 144,155 as well as the closely related naked 9,10-bis(trimethylsilyl)anthra-cene radical anion 145.156 This chemistry is further extended to the solvent-shared and solvent-separated alkali metal salts of perylene radical anions and dianions 146, 147,156 while other examples focus on alkali metal salts of 1,2-diphenylbenzene and tetraphenylethylene derivatives, where reduction with potassium in diglyme afforded contact molecules with extensive 7r-bonding, [l,2-Ph2C6H4K(diglyme)] 148.157 Extensive 7r-coordination is also observed in (1,1,4,4 tetraphenylbutadiene-2,3-diyl)tetracesiumbis(diglyme)bis(methoxyethanolate) 149.158... 

Kelly et al., 1974 Mollers and Memming, 1973). This method has the advantage that only absorbances synchronized with the electrode potential are detected. An example of the use of the technique is shown in Fig. 6, in which case the spectrum of the perylene radical anion was obtained even though the intermediate was reacting rapidly with acetic acid (Ahlberg et al., 1978). 

Fig. 6 Visible absorption spectra of the perylene radical anion in DMF containing acetic acid (70 mM) measured by modulated specular reflectance at 3 Hz (a), 10 Hz (b), 30 Hz (c), 60 Hz (d), and 80 Hz (e). (Ahlberg, et al., 1978)...

The complex mechanism of the protonation of anion radicals in DMF may have some bearing upon the mechanism proposed for the reaction of perylene radical anion with alcohols (Levin et a/., 1972) and anthracene radical anion with t-butyl alcohol (Rainus et a ., 1973). The disproportionation mechanism was proposed for these reactions in ethereal solvents with alkali-metal counter-ions. The principal evidence for the mechanism was the observation of rate laws of the form of (77) where was suggested to be... 

A different approach, MSRS, involves modulation of the electrode potential by a periodic function, e.g., a sine wave or a pulse [340-345]. Absorbance variations other than those that are synchronized with the modulation frequency are discriminated by help of a lock-in amplifier, leaving the system almost insensitive to absorbance of products built up during the experiment. In this way it has been possible to obtain the visible spectrum of perylene radical anion in the presence of acetic acid (Fig. 50) and thianthrene radical cation in the presence of water [341]. Other examples include the oxidation of N,N-... 

Figure 53. Absorbance-time curves for the spectroelectrochemical generation of perylene radical anion at 570 nm in DMF (a) without and (b) with addition of phenol. The time to open circuit (dashed line) is 400 ms. (From Ref. 359.)...

Li perylene radical anion Formation S.5.2.2.3 C2 H,2Li2 dilithioperylene Formation 5.S.2.2.3... 

Figure 8. Plots of Ae versus t and of log Kdisp versus 1 IT for Cs+, Pem in DME. Pe denotes the perylene radical anion. (See text for description of the slopes.) (Reproduced from reference 22. Copyright 1978 American Chemical Society.)...

Figure 10. The difference spectrum of flashed solution ofNa+,Pe in THF100 xs after a flash. Note the bleaching due to photodissociation of the perylene radical anion and the absorbance resulting from the formation of an excess of perylene. (Reproduced with permission from reference 23. Copyright 1976...

Table II. Rate Constants (ki and k2) for the Disproportionation of Perylene Radical Anions in Various Solvents Containing Different Counterions at 25 °C...

Isomerization. Finally, some investigations of unstable radical anions will be discussed. Radical anions of ds-stilbene rapidly isomerize to radical anions of trans-stilbene therefore, their spectra or relative electron affinities cannot be studied by conventional techniques. Flashing a solution of perylene radical anions mixed with cis-stilbene yields cis-stilbene radical anions, which persist for 200-300 jls before the ejected electrons are recaptured by the perylene formed by the photolysis. The difference spectrum of the photolyzed solution is shown in Figure 12. The concentration of the ds-stilbene radical anions formed can be determined by the degree of bleaching the absorption peak of the perylene radical anions. The absorption spectrum of cis-stilbene radical anions can also be determined in this way (19). Similar experiments, results of which are shown in Figure 13, permit the determination of the absorption spectrum of trans-stilbene radical anions. Because this spectrum has been established by other methods, the reliability of the flash-photolytic method can be determined by comparing the differ-... 

A solution of perylene radical anions containing a 1 1 mixture of cis- and trans-stilbenes is flash photolyzed. The ejected electrons are captured by... 

In polar solvents, however, there is no exciplex emission. The free radical ions are formed, and they can produce chemiluminescence by annihilation. The recombination reaction between perylene radical anion (14) and tetramethyl-p-phenylene diamine radical cation ( Wurster s Blue ) in 1,2-dimethoxyethan (= DME) was the first bright chemiluminescence of this type [34]. 

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. 

Chemiluminescence also occurs during electrolysis of mixtures of DPACI2 99 and rubrene or perylene In the case of rubrene the chemiluminescence matches the fluorescence of the latter at the reduction potential of rubrene radical anion formation ( — 1.4 V) at —1.9 V, the reduction potential of DPA radical anion, a mixed emission is observed consisting of rubrene and DPA fluorescence. Similar results were obtained with the dibromide 100 and DPA and/or rubrene. An energy-transfer mechanism from excited DPA to rubrene could not be detected under the reaction conditions (see also 154>). There seems to be no explanation yet as to why, in mixtures of halides like DPACI2 and aromatic hydrocarbons, electrogenerated chemiluminescence always stems from that hydrocarbon which is most easily reduced. A great number of aryl and alkyl halides is reported to exhibit this type of rather efficient chemiluminescence 155>. 

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.

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.

Reduction of trichloroethylene by a series of well-characterized outer-sphere electron-transfer reagents, viz. the radical anions of naphthalene, pyrene, perylene, decamethylcobaltocene, and cobaltocene, resulted in the formation of cis- and trans-dichloroethylene in ratio varying from 0.87 to 4.5, whereas in the reduction by vitamin B12, the ratio was 30 1. This indicated that reduction with vitamin B12 occurs with a non-outer-sphere electron-transfer mechanism. A mechanism involving initial formation of a radical ion followed by an ejection of a chloride to give d.v-dichlorovinyl radical and franx-dichlorovinyl radical has been proposed.284... 

Steady state illumination of polyaromatics in the presence of triphenylstan-nyl anion in THF gave rise to the aromatic radical anion [198]. In the case of perylene and tetracene the radical anions persisted for a long time. In fact, their decay is modulated by the relative value of the reduction potential of the aromatic and of the formed distannane. 

Nine years later, Leonhardt and Weller detected an excimer type emission in solutions containing perylene and dimethylaniline [80]. This first heteroexcimer has become the prototype of an ever expanding area of research. Perhaps the impact of these observations are best illustrated by the monograph dealing with the new phenomenom published only 12 years after the first report [81]. The significance of this research for the proper understanding of photo-induced electron transfer is born out by the first positive identification of a radical anion resulting from the irradiation of a donor-acceptor system in polar solvents (vide infra) [82]. 

Figure 16. Current decay curves the natural logarithm of the steady-state oxidation plateau current of radical anions (mediators) plotted against time (s) for the following four combinations of mediator/substrate benzophenone/l-bromo-2,2-dimethylpropane (-(-) perylene/l-bromo-2,2-dimethylpropane (x) perylene/l-bromoadamantane ( ) and quinoxaline/2-chloro-2-methyl-propane (O). All measurements were obtained with a 10-pm platinum disk electrode in DMF/0.1 M BU4NBF4 at 22°C. From S. U. Pedersen and K. Daasbjerg, Acta Chem. Scand, 43 30 (1989) [36],...

Figure 1. Lithium radical anions see Table 1 for refs. Lithium radical anions of (A) biphenylene, (B) fluorene, (C) perylene, (D) heptalene and (E) 4,4 -bipyridine.

In general, however, one must be concerned with the possible dominance of chemistry by small amounts of dianions. Although not seen in electrochemistry, the naphthalene dianion has been reported in the literature ll l5°-159 167) and could dictate the results of quench reactions. In the specific case of sodium naphthalene in tetrahydro-furan, kinetic analysis of a water quench directly implicites the radical anion as the chemically dominant species 150 -158-167>. In the case of the larger aromatic molecule, perylene, however, the dianion and not the radical anion is the species quenched167a). 

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