9,10-Diphenylanthracene oxidation

Examples include luminescence from anthracene crystals subjected to alternating electric current (159), luminescence from electron recombination with the carbazole free radical produced by photolysis of potassium carba2ole in a fro2en glass matrix (160), reactions of free radicals with solvated electrons (155), and reduction of mtheiiium(III)tris(bipyridyl) with the hydrated electron (161). Other examples include the oxidation of aromatic radical anions with such oxidants as chlorine or ben2oyl peroxide (162,163), and the reduction of 9,10-dichloro-9,10-diphenyl-9,10-dihydroanthracene with the 9,10-diphenylanthracene radical anion (162,164). Many other examples of electron-transfer chemiluminescence have been reported (156,165). 

Emission resulting from chemical oxidation of anion radicals has now been obtained under a variety of conditions. A summary of the conditions and a qualitative characterization of the reported results can be found in Table I. Several reported failures to observe emission have been included in the table where these results may have special significance. That the oxidizing power of the oxidant influences the emission can be seen by the finding that chlorine and bromine, but not iodine, act on the anion radical of 9,10-diphenylanthracene to produce emission. 

With aromatic hydrocarbons, the potential of this step is usually 0.5 V more negative than the first step. The dianions Q2 are more protophilic (basic) than Q and are easily converted to QH2 (or QH ), withdrawing protons from the solvent or solvent impurities (possibly water), although Q2 with delocalized charges can remain somewhat stable. With compounds like 9,10-diphenylanthracene and in protophobic solvents like AN, the formation of dications has been confirmed in the second oxidation step (Section 8.3.2) ... 

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. 

Fig. 8.19 Cyclic voltammogram for the oxidation of 9,10-diphenylanthracene (1 mM) at a platinum ultramicroelectrode in 0.5 M Bu4NCI04-AN. Scan rate 1000 Vs"1 [62].

Repeated cycling through the RUB reduction wave resulted in a decrease in size of the catalytic current. This occurred even when the solution was stirred between cycles. This behavior implies that a blocking or filming of the electrode occurred during the reduction process. Repeated cycling over the oxidation wave removed the film and reactivated the electrode. The electrochemical reduction of 9,10-diphenylanthracene (DPA), 1,3,6,8-tetraphenylpyrene (TPP), anthracene (ANT), fluoranthene FLU) and 2,5-diphenyl-l,3,4-oxadiazole (PPD) in the presence of S Os - all showed similar cathodic waves. 

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). 

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) ) ... 

Certain aromatic hydrocarbons, such as 9,10-diphenylanthracene, give relatively stable radicals and cation radicals upon electrochemical reduction and oxidation, respectively. If one arranges to have the radical ions from both processes mixed, either by normal DC electrolysis in a suitably designed cell or by using an alternating current for the electrolysis, the phenomenon of electrochemiluminescence appears (Hercules, 1971 McCapra, 1973). 

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... 

The criteria for SHAC voltammograms to yield reversible potentials are that the zero-current crossing potentials must be both frequency- and phase-independent. In practice one measures the in phase (/) and quadrature (Q) components of the second harmonic a.c. current by means of a phase-sensitive detector or lock-in amplifier. The response is illustrated in Figs 10-12 obtained during measurements on the oxidation of 9,10-diphenylanthracene (DPA) in acetonitrile (Fig. 10) and in acetonitrile containing pyridine (Figs... 

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]... 

Dithianes and gemdithioacetals could be alternatively oxidized indirectly by means of the redox catalysis method. The technique appeared to be particularly mild and mainly avoided inhibition and adsorption phenomena relative to the anode platinum interface. Thus aromatic hydrocarbons (e.g. 9,10-diphenylanthracene) [83] and judiciously substituted triphenylamines [84] afford quite stable cation radicals used homogeneously as oxidants. Their standard potential, E°x, will determine the rate of electron exchange with the concerned sulfur compound. The cleavage of a C—S bond in any dithiane can be regarded as fast enough to draw the redox catalysis process to the indirect oxidation. 

Among the many cation radicals originated by oxidation of various aromatic compounds47 9,10-diphenylanthracene (DPA) and perylene have been proposed as initiators of cationic or radicalic polymerizations of various monomers. 

Reaction of oxazoles with singlet oxygen generated from the thermal decomposition of 9,10-diphenylanthracene peroxide gives oxidation products identical to those observed in dye-sensitized photooxygenations.866-368... 

Figure 1.1.2 Representation of (a) reduction and (b) oxidation process of a species, A, in solution. The molecular orbitals (MO) of species A shown are the highest occupied MO and the lowest vacant MO. These correspond in an approximate way to the E s of the A/A and A /A couples, respectively. The illustrated system could represent an aromatic hydrocarbon (e.g., 9,10-diphenylanthracene) in an aprotic solvent (e.g., acetonitrile) at a platinum electrode.

Use of iodine-silver perchlorate may accomplish cation-radical formation before the oxidizing pair can themselves react. In modern usage, silver ion (as the perchlorate usually) is added to a solution of the substrate and iodine, and the complexity of the iodine-silver perchlorate system is avoided, provided that the substrate undergoes reasonably fast oxidation. Such is the case with perylene (Sato et al., 1969 Ristagno and Shine, 1971) and pheno-thiazine, but not the case with diphenylanthracene and thianthrene (Shine et al., 1972). 

Numerous electrochemical studies of systems which form stable cation radicals exist. For example, the CV oxidation of aromatic hydrocarbons which have the sites of high electron density blocked, such as 9,10-diphenylanthracene (DPA) or rubrenc, show volt-ammograms typical of nernstian one-electron systems (Phelps et al., 1967 Marcoux et al., 1967 Peover and White, 1967). Rotating disk and RRDE studies also provide evidence for their stability. Controlled potential coulometric oxidation of these show napp-values of one and CV studies of the oxidized solution showed a cathodic peak for reduction of the cation radical at the same potentials and of the same height as that of the original solution. Similar electrochemical behaviour is observed with phenothiazines, thianthrenes, and other heterocyclic compounds in solvents suitably freed from nucleophilic impurities. Not only do the electrochemical results demonstrate the production of a stable cation radical, but the measured Ep- or... 

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