Stilbene radical-anion

St /G AG-0.14 V fluorescence quenching stilbene radical anion detected in transient absorption no Gs near injection site or in intervening sequence k = 1012-108 s 1 for 0-4 intervening A-T base-pairs (-3.4-17 A) exponential distance dependence of CT rate constant (3 0.6-0.7 A"1 small variations in k depending on whether G is in the A or T arm of the hairpin... 

St /G/GG AG 0.14 V change in k. of stilbene radical anion monitored by transient absorption Gs within 1-3 base-pairs of stilbene linker CT to further GG sites k = 2 x 105-8 x 107 s 1 1-2 bases (3.4-6.8 A) strong order of magnitude decrease in k per intervening A intrastrand CT faster through A than T bridges intrastrand CT faster than interstrand CT... 

Emission spectra have been recorded for electron injection into Au and Ag spherical electrodes and hole injection into Au(lll) planar electrodes. These processes were brought about in solutions of acetonitrile containing tetrabutylammonium hexafluoro-phosphate (TBAHP), using the trans-stilbene radical anion as the electron injector and the thianthrene radical cation as hole injector. The spectrum for the hole injection process into planar Au(lll) electrodes has been resolved into the P S-polarised components of the emitted light. A comparison of the spectral distribution of emitted light for the above electron injection process, occurring at both Au and Ag... 

Radical-anions from cis- and /ran. f-stilbene are distinct species with individual uv- and esr-spectra [7], The cw-form is metastable and slowly converts to the trans-form. The kinetic features of this interconversion have been studied by generating the cw-stilbene radical-anion in hexamethylphosphoramide by photochemi-cally assisted electron transfer from a second radical-anion of less negative... 

Similarly, the stilbene isomers (69) react with tertiary amines by ET followed by proton transfer and coupling, forming 70. " During the irradiation of cA-stilbene in the presence of ethyldiisopropylamine, the fratw-stilbene radical anion, tranr-69, was observed by Raman spectroscopy. " The ET mechanism is also supported by a pronounced dependence of the quantum yields on solvent polarity. 

The 1,1,4,4-tetraphenylbutane disodium salt was found to eject electrons scavenged by added 1,1-diphenylethylene [59, 60]. In the case of trans-stilbene dianion, the photoejection of an electron was accompanied by isomerization in ds-stilbene radical anion while biphenyl was used as electron scavenger [61]. ds-Stilbene itself was used as scavenger of electron photoejected from aromatic radical anions like sodium perylenide [46], These scavenging experiments are... 

CpLuCl2(THF)2 reacts with 2 equiv. of Na[PhCH= CHPh] in DME with dimerization of the stilbene radical anions to form [Na(DME)3][Cp2Lu /u.-CH(Ph)CH(Ph)-CH(Ph)CH(Ph) ] containing a dianionic 1,2,3,4-tetraphenyl-butadiene ligand. X-ray crystal structure determination shows Lu coordinated to two Cp rings and the dianionic butadiene ligand in an rj and 1,4-diyl fashion. ... 

An example of the latter process is seen in a study of the electrolysis of stilbene in DMF containing TBAI and tert-h xiy chloride [301] the electrogenerated radical anion of stilbene initially converts tert-b xiy chloride to the tert-h xiy radical, which interacts with the stilbene radical anion to afford a 3 2 mixture of 3,3-dimethyl-1,2-diphenylbutane and 1-phenyl-2-(4 = r rr-butylphenyl)ethane. 

Tertiary amines have been reported to undergo addition to singlet trans-stilbene product selectivity appears to be determined by the orientation of deprotonation of the aminium radical intermediate by the stilbene radical anion. Intramolecular addition has been observed in 5-2-(r-methylalkyl)-aniline (220) on irradiation in methanol to give the 25,3/ -2,3-dimethylindoline... 

Isomerization. Finally, some investigations of unstable radical anions will be discussed. Radical anions of ds-stilbene rapidly isomerize to radical anions of trans-stilbene therefore, their spectra or relative electron affinities cannot be studied by conventional techniques. Flashing a solution of perylene radical anions mixed with cis-stilbene yields cis-stilbene radical anions, which persist for 200-300 jls before the ejected electrons are recaptured by the perylene formed by the photolysis. The difference spectrum of the photolyzed solution is shown in Figure 12. The concentration of the ds-stilbene radical anions formed can be determined by the degree of bleaching the absorption peak of the perylene radical anions. The absorption spectrum of cis-stilbene radical anions can also be determined in this way (19). Similar experiments, results of which are shown in Figure 13, permit the determination of the absorption spectrum of trans-stilbene radical anions. Because this spectrum has been established by other methods, the reliability of the flash-photolytic method can be determined by comparing the differ-... 

Figure 14. Absorption spectra of cis- and trans-stilbene radical anions determined by flash photolysis. (Reproduced from reference 19. Copyright 1977 American Chemical Society.)...

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