9,10-Diphenylanthracene radical cation

Electrochemically generated solutions of radical-cations will react with nucleophiles in an inert solvent to generate a radical intemiediate. Under these conditions the intermediate is oxidised to the carboniiim ion by a further radical-cation. Generally, an aromatic system is then reformed by loss of a proton. Reactions of 9,10-diphenylanthracene radical-cation nucleophiles in acetonitrile are conveniently followed either by stop flow techniques or by spectroelectrochemistry. Reaction with chloride ion follows the course shown in Scheme 6.2, where the termination... 

Obviously, Ag is unity when B is stable. The working curve for the eCeh mechanism, which has been considered for the pyridination of 9,10-diphenylanthracene radical cation (DPA ) [349], is illustrated in Fig. 51. 

Figure 51. Chronoabsorptometry working curves for the eCe mechanism. The experimental points are for the reaction between the 9-10-diphenylanthracene radical cation and pyridine at different concentration ratios (From Ref. 349.)...

Likewise, 9,10-diphenylanthracene (an aromatic hydrocarbon that cannot release hydrogen, as in steps (ib) or (ic)) reacts with PDM and with PTM giving PDM- and PTM respectively (152), together with 9,10-diphenylanthracene radical-cation hexachloroantimonate, which has been fully characterized (Ballester et ai, 1971c). 

The rates of electron-transfer processes in the oxidation of polycyclic aromatic hydrocarbons have been considered by Peover and White, who estimated from cyclic voltammograms the apparent standard rate constant for 9,10-diphenylanthracene radical cation formation to be of the order 1 cm... 

Scheme 6.2. Reaction or9,10-diphenylanthracene radical-cation with chloride ion.

The two-step oxidation really occurs, for example, with 9,10-diphenylanthracene. As shown by the CV curve in Fig. 8.19, the two waves are reversible or nearly reversible. The radical cation of 9,10-diphenylanthracene is fairly stable and, as in the case of radical anions, its ESR signals can be measured. 

The radical cation of 9,10-diphenylanthracene is much more stable than that of anthracene, because, with 9,10-diphenylanthracene, the 9- and 10-positions, which are reactive because of the high unpaired-electron densities, are masked by phenyl groups and the unpaired electrons are delocalized. The stabilization of the radical cation of anthracene also occurs by introducing other substituents like -NH2 and -OCH3 in the 9,10 positions. 

However, the cell in Fig. 9.2(b) has a disadvantage in that the concentration of the electrogenerated substance decreases with increasing distance from the OTE surface. Because of this, simulation of the reaction is very difficult, except for the first order (or pseudo-first-order) reactions. For more complicated reactions, it is desirable that the concentration of the electrogenerated species is kept uniform in the solution. With a thin-layer cell, a solution of uniform concentration can be obtained by complete electrolysis, but it takes 30 s. Thus, the thin-layer cell is applicable only for slow reactions. For faster reactions, a column-type cell for rapid electrolysis is convenient. Okazaki et al. [7] constructed a stopped-flow optical absorption cell using one or two column-type cells (Fig. 9.4) and used it to study the dimerization of the radical cations (TPA +) of triphenylamine and the reactions of the radical cation (DPA +) of 9,10-diphenylanthracene with water and alcohols. Using the stopped-flow cell, reactions of substances with a half-life of 1 s can be studied in solutions of uniform concentrations. 

Bard etaL 5S6>5571 and Visco etaL 558) have quantitatively analyzed the intensity of pulsed ECL of 9,10-diphenylanthracene, tetraphenylpyrene and rubrene. By computer simulation of the electrode process and the subsequent chemical reactions the rates for chemical decay of the radical ions could be determined. Weaker ECL with fluorescence emission 559 or electrophosphorescence S60) occurs if the radical anion R - reacts with a dissimilar radical cation R,+ of insufficient high oxidation potential to gain enough energy for fluorescence emission, that is, if ht fluorescence) >23.06 (Ej >+. -Ej -.), e.g., in the annihilation of the anthracene radical anion with Wurster s blue. For these process the following schemes are assumed (Eq. (242) ) ... 

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... 

An ECE mechanism examined with the rotating disc electrode technique involved the pyridination of 9,10-diphenylanthracene (DPA) in acetonitrile/0.2 M tetraethylammonium perchlorate (Manning et al., 1969). Initially, 9,10-diphenylanthracene undergoes a reversible one-electron oxidation (84a) to form the radical cation, which reacts with pyridine (Py) to form an adduct (84b) which is in turn oxidized (84c) at a less positive potential than the initial diphenylanthracene molecule. This reaction sequence leads to formation of a dication that may further react with pyridine to form the final... 

A much-used approach to the study of the primary electrochemical step of aromatic hydrocarbons involves the use of model compounds whose corresponding radical cations (and in some cases dications) are relatively stable. Substituted anthracenes, particularly 9,10-diphenylanthracene (9,10-DP A), have featured largely in such work [12,53-58,135,137,151,163-168]. For instance, on slow-sweep CV in MeCN, purified without... 

The direct nature of attack of CN on radical cations of aromatic compounds has been demonstrated by CV [221]. The reversible one-electron oxidation of anthracene becomes irreversible in the presence of CN, and 2 F electrolysis gives a mixture of cyano and isocyano addition across the 9,10-position. Interestingly, it appears that cyanation of 9,10-diphenylanthracene gives the 9,10-diphenyl-9,10-dicyano-9,10-dihydroanthra-cene only [233]. 

R SR Gem-dithioacetals C / R SR 9,10-Diphenylanthracene and triarylamines Rapid decomposition of radical cation by cleavage (R = aromatic) or nucleophilic attack (R = aliphalic) (oxidative deprotection of carbonyl compounds) [117]... 

Mengoli and Vidotto in 197158 proposed the use of the electrogenerated radical cation of 9,10-diphenylanthracene as initiator for cationic polymerization of styrene and n-butyl vinyl ether (NBVE). 

Later the same authors61 published a study on the reactivities of a number of electrogenerated radical cations toward St and isobutyl vinyl ether (IBVE). The reactivity comparison was made among 9-phenylanthracene (9PA), 9,10-dimethyl-anthracene (DMA), 9,10-diphenylanthracene (DPA), 1,3,6,8-tetraphenylpyrene (TPP), rubrene (RU), triphenylene (TP), perylene (p). The stability of the ion radicals, in the absence of the monomers, is in the order ... 

In general, radical cations are less stable than their anionic counterparts, but relatively stable cations can be obtained from reactants in which those positions which carry the highest charge density in the radical are blocked with respect to either proton loss or nucleophilic attack. For example the 9,10-diphenylanthracene and rubrene radical cations are sufficiently stable to give reversible cyclic voltammo-grams. Radical cations appear to be more stable in nitrobenzene than in acetonitrile solutions. Coating of the anode with insoluble insulating polymeric ffims is a common hazard in anodic oxidation systems but it can be alleviated by the use of scraped electrodes and periodic polarity-reversal techniques. 

Whilst OTEs have been successfully used to investigate a wide range of reaction types, the major application has been in the study of systems which involve coupled chemical reactions. An example of this type of study is that of the oxidation of diphenylanthracene (DPA) in the presence of water by Bjount Kuwana [9]. By monitoring the absorbance due to the radical cation of DPA, the first oxidation product, the reaction was shown to follow the scheme... 

The relatively recent development of electrochemical methods for the synthesis of stable cation-radical salts, such as the perylene (18a) and 9,10-diphenylanthracene (18b) cation-radicals has permitted their use as initiators for vinyl ether polymerizations. 

Radical anions have also been obtained from such condensed systems as azulene [122, 123], 4,6,8-trimethylazulene [122], acenaphthylene [124], and sym-dibenzocycloctatetraene [125]. Radical cations of phenanthrene [117] and of 9,10-diphenylanthracene [69] have been obtained by oxidative electrochemical generation at platinum electrodes. 

Here, eB is the molar absorption coefficient of substance B, and CA and DA are the concentration and the diffusion coefficient, respectively, of substance A. The A(t)-t relation changes when reaction (9.2) occurs. By simulating the expected A(t)-t relation and comparing with the experimental results, the rate constant k can be obtained. This method is useful for studying the reaction of radical ions in non-aqueous solutions. For example, the reactions of the cationic radical (DPA +) of 9,10-diphenylanthracene (DPA) with such bases as water and pyridine were... 

Research has uncovered a general tendency for very fast, energetic electron-transfer reactions to yield electronically excited products that may reveal themselves via luminescence [66,82-90]. A prototype of this chemistry is the reaction between the anion and cation radicals of 9,10-diphenylanthracene (DPA) in acetonitrile ... 

In organic ECL reactions, the luminescent species are generally derivatives of polyaromatic hydrocarbons where A and B in Eqs. (1) through (4) can be either the same species (leading to self-annihilation) or two different PAHs with either being the analyte (mixed system). Some examples of both self-annihilation and mixed system ECL reactions of organic molecules are listed in Tables 1 and 2. One well-studied example is the self-annihilation reaction between the anion and cation radicals of 9,10-diphenylanthracene (DPA) via an S-route in acetonitrile resulting in blue fluorescence characteristic of DPA [17] ... 

Figure 14 Diagram of ECL laser. A, A, A, A + represent the ground, excited, anion radical, and cation radical states of 9,10-diphenylanthracene, respectively. (From Ref. 66. With permission from McMillin Publishers, Ltd.)...

Both single-sweep and cyclic voltammetry can provide information about the approximate number of electrons transferred in each wave or peak. This is done by comparing the plateau or peak height with that of a known one- or two-electron transfer process under identical conditions (as an example, the oxidation of 9,10-diphenylanthracene to the cation radical is a commonly used reference reaction). 

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