Anthracene 9,10-diphenylanthracene

The main features of the chemiluminescence mechanism are exemplarily illustrated in Scheme 11 for the reaction of bis(2,4,6-trichlorophenyl)oxalate (TCPO) with hydrogen peroxide in the presence of imidazole (IMI-H) as base catalyst and the chemiluminescent activators (ACT) anthracene, 9,10-diphenylanthracene, 2,5-diphenyloxazole, perylene and rubrene. In this mechanism, the replacement of the phenolic substituents in TCPO by IMI-H constitutes the slow step, whereas the nucleophilic attack of hydrogen peroxide on the intermediary l,l -oxalyl diimidazole (ODI) is fast. This rate difference is manifested by a two-exponential behavior of the chemiluminescence kinetics. The observed dependence of the chemiexcitation yield on the electrochemical characteristics of the activator has been rationalized in terms of the intermolecular CIEEL mechanism (Scheme 12), in which the free-energy balance for the electron back-transfer (BET) determines whether the singlet-excited activator, the species responsible for the light emission, is formed ... 

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). 

Thus, 9,10-diphenylanthracene ( p = — 1.83 V vs. SCE) is reduced at too positive a potential and hence its rate of reaction with the sulphonyl moieties is too low. On the other hand, pyrene (Ep = — 2.04 V) has a too negative reduction potential and exchanges electrons rapidly both with allylic and unactivated benzenesulphonyl moieties. Finally, anthracene Ev = —1.92 V) appears to be a suitable choice, as illustrated in Figure 3 (curves a-d). Using increasing concentrations of the disulphone 17b, the second reduction peak of XRY behaves normally and gives no indication of a fast electron transfer from A. 

Similar results were obtained with the diperoxides 5 (R phenyl) and 5 a (R />-chlorophenyl) and dibenzanthrone or other fluorescers (perylene, rhodamine B, 9.10-diphenylanthracene, anthracene, fluorescein), with quantum yields of the respective chemiluminescence in the range 3.29 X 10 8.... 5.26 X 10 6. 

From all anthracene endo peroxides investigated so far (71> 1>, p. 132) the compound 7 (1.4-dimethoxy-9.10-diphenylanthracene 1.4-endoperox-ide) was found to exhibit the most efficient chemiluminescence 72> on... 

As reported by T. Wilson 71>, the emitter is the anthracene derivative 9 which can be replaced by rubrene, but not by 9.10-diphenylanthracene. 

In the pioneering papers of Wawzonek et al. [18, 214] it was demonstrated that CO2 can be added to cathodicaUy reduced hydrocarbons to yield dihydrodi-carbonylates. Examples of this kind of reaction include naphthalene [215-220], anthracene [18], 9,10-diphenylanthracene [18], phenanthrene [215, 216], butadiene [217-220], stilbene [18], and diphenyl... 

Both compounds 190 and 193 are reduced to 9,10-diphenylanthracene (205) by zinc and acetic acid. However, more interest attaches to the formation of anthracenes from anthracen-9,10-imines in nonreducing conditions. The iV-ethoxycarbonyl derivative (192) decomposed at 215° in cyclohexane to 33% of 205, although curiously this product was not obtained if the solvent was previously degassed. Whether or not the reaction involves simple extrusion of ethoxycarbonyl nitrene could not be established, since the expected iV-cyclohexylurethane was not detected. The 9,10-epithioanthracene (194) loses sulfur thermally to give 205. ... 

In a related reaction (see also Section III, H) the anthracen-9,10-imine (187) with dimethyl acetylenedicarboxylate at 180° gave 26% 1,4-dimethyl-9,10-diphenylanthracene (209) and 14% of its Diels-Alder adduct with the acetylenic ester, the 9,10-ethenoanthracene (210). No nitrogen-containing product was isolated, and the related compounds 188 and 189 failed to react with the acetylenic ester. 

Carbon disulfide quenches the fluorescence of anthracene quite efficiently,145,149 but seems to have little effect on its triplet lifetime.147 Diphenylanthracene in benzene fluoresces with a quantum yield of 0.8 and shows a high sensitivity to the oxygen concentration in photooxygenation reactions. With about 1 vol% of CS2 present, AC>2 is practically independent of [02] (> 10"5 mole/liter). In jjoth cases, where carbon disulfide was either used as solvent or was added to an otherwise strongly fluorescent solution, the quantum yields of photooxygenation followed... 

Parker and Joyce125 have also observed a new band in the delayed emission spectrum of solutions of anthracene (A) and 9,10-diphenylanthracene (B) in ethanol at — 75°C, which they attribute to the exciplex of these species formed in the process of mixed triplet-triplet annihilation... 

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. 

Cyclic peroxides may serve as a source of singlet oxygen. Wasserman et reacted 9,10-diphenylanthracene peroxide (238, conveniently prepared as in Nilsson and Kearns ) with 138 to give 140 rubrene peroxide proved to be considerably less efficient. Decomposition of anthracene peroxide alone takes another course. 32.396 jg treated with phthaloyl peroxide... 

In some molecules, the interaction can develop into a stronger force and the interplanar distance further reduced to form stable photodimers through covalent bonds. For example, anthracene forms a photodimer and no excimer emission is observed, whereas some of its derivatives with bulky substituents which hinder close approach give excimer fluorescence. In 9-methylanthracene both photodimer formation and excimer emission is observed. 9, 10-diphenylanthracene neither forms a photodimer nor emits excimer fluorescence due to steric hindrance. These observations are tabulated in the Table 6.3, which shows that the nature of the excited state is also important. 

Stevens401 irradiated anthracene, 9-phenylanthracene, and 9,10-diphenylanthracene at 3600 A and 280-300°C. He found that both 02 and NO quenched the fluorescence with similar efficiencies. For anthracene at 280°C and 9-phenylanthracene at 300°C, the ratios of the quenching rate constant for NO to the fluorescence rate constant are, respectively, 1120 and 1380 M 1. Ware and Cunningham4384 found the rate constant to be 1.97 x 1011 M 1 sec-1 for the quenching of anthracene vapor by NO at 280°C. They also found the anthracene-fluorescence constant to be 3.51 x 107 sec-1. The ratio of their two rate constants is 5500 M-1, about a factor of five larger than that found by Stevens. 

Evidence for adiabatic photolytic cycloreversions at room temperature has been obtained more frequently in recent years [121,122], The adiabatic generation of singlet oxygen by photochemical cycloreversion of the anthracene and 9,10-dimethylanthracene endoperoxides 105 and 106 proceeds with wavelength-dependent quantum yields of 0.22 and 0.35, respectively, and involves the second excited singlet state of the endoperoxides [123]. Photodissociation of the 1,4-endoperoxide from l,4-dimethyl-9,10-diphenylanthracene was found to yield both fragments, i.e., molecular oxygen and l,4-dimethyl-9,10-diphenylanthracene, in their electronically excited state [124]. 

Anthracene undergoes a photochemical 9,10,9, 10 -cycloaddition which goes through the excimer as intermediate. Many aromatic molecules follow similar cycloaddition paths. The close approach of the molecules in the excimer is essential for bond formation, and steric hindrance can prevent the reaction unsubstituted anthracene dimerizes so fast that no excimer fluorescence can be detected, 9,10-dimethylanthracene shows both excimer fluorescence and photodimerization, but 9,10-diphenylanthracene shows neither excimer emission nor photodimerization (Figure 4.52). 

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. 

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) ) ... 

As the size of the substituents on the central carbon atoms is increased, the longitudinal (long-axis) and lateral (short-axis) slip of the stacked molecules also increases, until a solid-state arrangement with coplanar anthracene rings that do not overlap is achieved. This arrangement is best exemplified by the well-known 9,10-diphenylanthracene (16) (Fig. 14.11) [30],... 

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