Anthracene photolysis

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). 

Jones218 has described an unusual photochemically initiated rearrangement of a silene-anthracene adduct to a silene which is part of an eight-membered ring (Eq. 60). Photolysis of the adduct 190 was believed to form the silaallylic diradical 191, whose canonical form 192 affords the... 

Attempts to produce dimers of naphthalene similar to those observed for anthracene (Chapter 2) have been unsuccessful, although three naphthalene derivatives have been reported to produce dimer (65) upon photolysis<78) (the structure of these dimers have been the object of some debate, however) ... 

The photochemistry of unsaturated nitro compounds has been investigated by Chapman and co-workers.<63) Photolysis of 9-nitro-anthracene in degassed solutions leads to anthraquinone and 10,10 -bianthrone ... 

Midinger and Wilkinson<54> have used flash photolysis and fluorescence quenching by heavy atoms to determine the intersystem crossing efficiencies of anthracene and a number of its derivatives. As discussed in Section 5.2b, heavy atoms present as molecular substituents or in the solvent serve to promote multiplicity forbidden transitions. When anthracene is excited the following processes can occur ... 

Examination of DABA photolysis in cyclohexane instead of benzene solution leads to predictably different results. The laser spectroscopy shows that 3BA is formed but, in this solvent, the triplet carbene undergoes an additional rapid reaction to generate the mesitylbora-anthryl radical (BAH ). This radical is identified by comparison of its spectrum with that of an authentic sample prepared from dihydrobora-anthracene. The half-life of... 

The products obtained from photolysis of DABA in cylcohexane support the assignments made above. The major product is the dimer formed from the coupling of BAH. This is accompanied by the other expected radical products, dihydrobora-anthracene and cyclohexybora-anthracene, as is shown in (19). 

Photolytic. Benzo[a]anthracene-7,12-dione formed from the photolysis of benzo[a]an-thracene (Z = 366 nm) in an air-saturated, acetonitrile-water solvent (Smith et al., 1978). 

In 1972 Berry and co-worker detected 3,4-pyridyne (101) by MS. Trapping experiments also provided evidence for the existence of this intermediate, although the chemistry of 101 differs considerably from that of o-benzyne. Thus, neither anthracene nor dimethylfulvene form Diels-Alder adducts with 101. Nam and Leroi were able to generate 101 in nitrogen matrices at 13 K and characterized it by IR spectroscopy. Irradiation of 3,4-pyridinedicarboxylic anhydride (103) with 1 > 340 nm results in formation of 101, which upon short wavelength photolysis (k > 210 nm) fragments to buta-l,3-diyne (104) and HCN, and to acetylene (105) and cyanoacetylene (106, Scheme 16.24). The assignment of an intense... 

Photoreduction was quenched by high concentrations of biacetyl, slightly retarded by iodonaphthalene, but not affected by azulene or anthracene.113 These observations led to the unsatisfying conclusion that reduction proceeded via a triplet state which could be only selectively quenched. However, later work114 using flash photolysis showed that the benzophenone ketyl radical was generated upon irradiation of solutions of benzophenone and acridine, and that its predominant mode of disappearance was by reaction with... 

P 15.6 Does Direct Photolysis Affect the Phenanthrene-to-Anthracene Ratio in Aerosol Droplets ... 

Gschwend and Hites (1981) observed that the two closely related polycyclic aromatic hydrocarbons, phenanthrene and anthracene, occur in a ratio of about 3-to-l in urban air. In contrast, sedimentary deposits obtained from remote locations (e.g., Adirondack mountain ponds) exhibited phenanthrene-to-anthracene ratios of 15-to-l. You hypothesize that these chemicals are co-carried in aerosol droplets from Midwestern U.S. urban environments via easterly winds to remote locations (like the Adirondacks) where the aerosol particles fall out of the atmosphere and rapidly accumulate in the ponds sediment beds without any further compositional change (i.e., the phenanthrene-to-anthracene ratio stops changing after the aerosols leave the air). If summertime direct photolysis was responsible for the change in phenanthrene-to-anthracene ratio, estimate how long the aerosols would have to have been in the air. Comment on the assumptions that you make. What are your conclusions ... 

At very short times, very little motion of reactants has occurred so that little, if any, reaction will have taken place. But the manner of creation of the mixture of A and B reactants should be considered. A very simple means of preparing a reaction mixture is by photolysis. For instance, consider a solution of anthracene and carbon tetrabromide. Photostimulation of anthracene with an extremely short duration light pulse produces excited singlet (and triplet) states. The carbon tetrabromide quenches the excited singlet state fluorescence very efficiently. Just before the photostimulation event, the quencher (i.e. B) is randomly distributed throughout the system volume and for a short time after photostimulation, it remains randomly distributed. With the exception of the location where the fluorophor A is, there is no preferred location of the quencher B. No... 

Kusuhara and Hardwick271 examined the quenching efficiency of NO for triplet anthracene and naphthacene dissolved in hexane at temperatures between —30 and 20°C. At 20°C, the respective quenching constants are 1.5 x 108 and 2.1 x 108 A/-1 sec-1, with activation energies of 5.6 and 2.4 kcal/mole. Their quenching constant for anthracene is considerably lower than the room-temperature value of 4 x 10s A/-1 sec-1, which was reported earlier by Porter and Windsor351 from their flash-photolysis studies. 

Triplet states for naphthalene, anthracene, and other aromatic compounds had been identified by absorption spectroscopy mainly with the aid of flash photolysis by G. Porter and his co-workers.22 Although a triplet state of benzene had been identified in a glassy matrix and had been associated with a long-lived emission of 10 sec or more duration,5 no evidence for the existence of this state by spectroscopic means had been produced until recently.23 Thus it has been known for some time that benzene in a glassy matrix when irradiated at wavelengths around 2500 A produces molecules which cross over to a triplet state with a relatively high probability. 

Carbene 132 is implicated in the photolysis of 1 since the observed289 photodimerization to 9,10-dihydrophenanthrene and -anthracene is best explained by head-to-head and head-to-tail coupling of this species. Moreover, the fact that allene 134 is isolated289,290 as the major product from irradiation of diesters 31 (equation 35) is fully consistent with a photo-Wolff rearrangement of the carbene. The minor product here involves cyclization... 

The photolysis of anthracene-benzene adducts 111 and 112 has been studied in detail [128], Photodissociation of 111 was found to give electronically excited anthracene with a quantum yield of 0.80, but the isomeric 47i + 27i adduct 112 photodissociates mainly diabatically, leading to electronically excited anthracene with a quantum yield of 0.08. The different efficiencies of adiabatic cycloreversions have been rationalized by correlation diagrams involving doubly excited states. Evidence for biradicals as intermediates in the photolyses of 111 and 112 has not been obtained. 

The 1,4-addition of heterocycles to aromatic systems has been reported. Photolysis of piperidine in benzene, for example, leads to the formation of the -substituted piperidine (222).204 Pyrrole, on photolysis in benzene, behaves differently and yields the 2-substituted pyrrole (223).208 In both instances, excitation of benzene, probably to the triplet, appears to be the initial step in the photolysis. The photolysis of iV-nitrosopiperidine in the presence of anthracene also results in 1,4-addition and the formation of an anthrone oxime,... 

Anthracene and certain other polynuclear hydrocarbons have long been known to dimerize readily on photolysis the formation of such dimers [Eq. (68)] is also the result of 1,4-addition, and is believed to involve a singlet excited state. With substituted anthracenes, the head-to-head dimer is generally formed, although there are exceptions to this rule. Dimerizations probably of a similar nature, have been reported for a number of azaanthracenes including 1-azaanthra-cene,270,271 2-azaanthracene,271 and benz[6]acridine.272 The precise structure of these dimers in uncertain. 

Photolysis, in the presence of oxygen, of alkenes containing an ally lie hydrogen atom leads to the formation of hydroperoxides. The sensitized process is more efficient, and often yields photoproducts different in structure from those obtained by nonsensitized photooxidation. Cyclohexadiene and related dienes on photolysis in the presence of oxygen yield the transannular peroxides. Thus, on photosensitized oxidation, a-terpinene (410) is converted into ascaridole (411).435 The equivalent process is not, in general, observed in acyclic dienes. Certain polynuclear aromatic hydrocarbons, such as anthracene and naphthacene and including the heterocycles 5,10-diphenyl-1-... 

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