9,10-Dicyanoanthracene, photoinduced electron transfer

Nakamura and co-workers provided detailed mechanistic information for the photoinduced electron transfer from tri-1 -naphthyl phosphate and related compounds to 9,10-dicyanoanthracene yielding binaphthyls The intramolecular nature of the reaction could be established by using laser flash photolysis experiments as well as fluorescence measurements [17],... 

C-C Cleavage in Epoxides. Radical cations generated by photoinduced electron transfer from epoxides (130) or aziridlnes (131) also ring open, giving oxidative products in the presence of oxygen. For example, dicyanoanthracene sensitizes the conversion of aryl epoxides to ozonides, eq. 48,... 

Silyl carbamates have recently been shown to undergo photoinduced electron transfer with substituted alkenes, in the presence of catalytic amounts of dicyanoanthracene and biphenyl (BP), to yield more complex carbamates182. Two examples which illustrate the complex structures created in good yield are shown in Scheme 61. 

From electrochemical studies it is known that an irreversible oxidation of C6o occurs at +1.76 V vs SCE in benzonitrile [165]. One of the first methods to generate the radical cation by radiation was performed by "/-irradiation of C6o in glass matrix at 77 K [166], A new absorption in the near IR at 980 nm was assigned to the C 6o (Fig. 19) [19]. Despite the sufficiently high reduction potential of +2.0 V of dicyanoanthracene, first attempts to generate the radical cation by photoinduced electron transfer were unsuccessful [Eq. (5)] [19]. One reason may be a fast back-electron transfer that competes with ionic dissociation in benzonitrile [19]. 

Redox photosensitization or co-sensitization by aromatic hydrocarbons has been utilized for enhancement of the efficiency of photoinduced electron transfer reactions. For example, the efficiency of the 9,10-dicyanoanthracene-sensitized photooxygenation of 1,2-diphenyloxirane in acetonitrile is enhanced appreciably by adding biphenyl as a co-sensitizer, giving 3,5-diphenyl-1,2,4-trioxolane in good yield [31-32]. This photoreaction does not take place in the absence of biphenyl. Schaap proposed that in this photoreaction the primary electron transfer reaction occurs from biphenyl (BP) to DCA to produce biphenyl radical cation BP and DCA . The secondary electron transfer from the oxirane to BP produces BP and the radical cation of the oxirane which is converted into the trioxolane (Scheme 5). 

In the presence of 9,10-dicyanoanthracene, irradiation of methanolic 1,4-diphenylbuta-l,3-diyne yields four MeOH adducts.Time-resolved studies indicate that a photoinduced electron-transfer process is involved. Irradiation... 

The probe wavelength dependence of the TG signal was measured for a photoinduced electron-transfer system between 9,10-dicyanoanthracene and 1-methylnaphthalene [53]. Owing to its superior sensitivity, the transient absorption spectra could be obtained without using too high of an excitation power. The decay kinetics were analyzed in terms of the back electron transfer to the ground state within 1 1 and 1 2 complexes. 

The thermal grating method was applied to a free ion yield measurement after a photoinduced electron-transfer reaction [98], The principle was similar to the measurement of (j)isc by the diffusive component of the Dens.G. The free ion yields in the photoinduced electron transfer from various donors to 9,10-dicyanoanthracene were determined from the ratio of the fast and slow rising intensities. The later one came from the released energy by the recombination reaction of the free ions and the former one came from the other processes (energy diagram Fig. 11). The quantum yield decreased from 0.5 to about 0 by changing the donor from biphenyl to N,N-dimethylaniline [different ox(Z))]. The determined [Pg.290]

A variety of permethylpolysilanes irradiated in mixed solvents (CC14-1,2-dichloroethane) containing 9,10-dicyanoanthracene resulted in chlorinative cleavage of the silicon-silicon bond yielding chlorosilanes and hexachloroethane in high yields. The results were interpreted as due to photoinduced electron transfer from the polysilane to the excited singlet state of the dicyanoanthracene149-152. 

The radical anions of tram- and c/s-stilbene can be distinguished by ESR [503]. A radical ion pair has been observed by this method using trial-kylamines in acetonitrile [497], Electron back transfer (i.e., a reaction of the radical anion of frans-stilbene with the radical cation of the donor) opens a new pathway for intersystem crossing to the tram triplet state. Time-resolved resonance Raman spectroscopy of photoinduced electron transfer from amines to frans-stilbene has been reported [497,504], In the photooxidation of frans-stilbene the radical cation has been observed by flash photolysis using cyanoanthracenes [505-507], The radical cations of cis-and frans-stilbene were also produced by electron transfer from biphenyl to excited 9,10-dicyanoanthracene and subsequent electron transfer from stilbene to the radical cation of biphenyl [508]. External magnetic field effects... 

Hasegawa, E., Koshii, S., Horaguchi, T, and Shimizu, T, Photoinduced electron transfer reaction of 1-substituted 2,3-diphenylaziridines with 9,10-dicyanoanthracene and chloranil, /. Org. Chem., 57, 6342,1992. 

The formation of the [3 -I- 2]-cycloadduct 55 can be explained by two different reaction pathways (Scheme 24). Irradiation at 300 nm leads to ring opening of the azirine 54 to the nitrile yKde as an intermediate, which adds to C o yielding the observed product 55. No product formation is observed at wavelengths >400 nm. Instead, under photoinduced electron transfer conditions in the presence of 9,10-dicyanoanthracene (DCA), the [3 -I- 2] -cycloaddition reaction proceeds via the 2-azaaUenyl radical cation. 

The 9,10-dicyanoanthracene (DCA)-sensitized c/s,tram-photoisomerization of highly electron-rich 1,2-diarylcyclopropanes and diarylmethylenecyclopropanes efficiently proceeds via a radical cation chain transfer mechanism.The photoisomerization of electron-rich l-diarylvinylidene-c/s-2,3-dimethylcy-clopropane (c-2d) in acetonitrile was also sensitized by DCA via photoinduced electron transfer. The photoisomerization efficiently takes place to give a 3 7 PSS mixture of c-2d and t-2d. However, the less electron-rich 1-diarylvinylidenecydopropanes c-2a-c under the same reaction conditions slowly isomerized... 

Mattay and coworkers extended the investigations of photoinduced electron tansfer from C6o to excited sensitizers and cosensitizers (Scheme 4) [173-175], They used dicyanoanthracene (DCA), dicyanonaphthaline (DCN), A-methylacri-dinium hexafluorophosphate (MA+), and triphenylpyrylium tetrafluoroborate (Tpp+) as sensitizers. In the case of DCA, DCN, and MA+, the addition of a cosensitizer (biphenyl) was necessary to produce the fullerene radical cation in sufficiently high yields [175], Otherwise, fast back-electron transfer seems to be predominant. However, by using TPP+ the formation of Q,o could be detected by EPR measurements even in the absence of a cosensitizer. This can be explained by (1) the high reduction potential (Ejed = 2.53 V vs SCE) and (2) the neutral form of the reduced sensitizer (electron shift) [174-176], Nevertheless, no influence of the cosensitizer on the EPR signal was observed under irradiation [175],... 

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