Solvent influence on the electrochemical reduction of photochemically generated cis-azobenzene

Grampp, Günter; Mureşanu, Claudia; Landgraf, Stephan

doi:10.1016/j.jelechem.2005.02.003

Cited by 13 publications

(9 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Our work clarifies the mechanism and generality of previous observations regarding the electrochemical switching of Z azobenzenes, 13,20 and follows similar observations of electrochemical switching in diarylethenes, 23,26,27 stilbenes, 45,46 and thioindigos. 47,48 Through the use of computational methods, we elucidate that the potential energy surface of the radical anion allows for a dramatic increase in the rate of thermal Z → E isomerization.…”

Section: ■ Conclusionsupporting

confidence: 89%

“…Integrating the region of the cyclic voltammogram where the Z → E isomerization takes place yields a current only approximately 5% of the value required to reduce the entire amount of azobenzene present in solution to the radical anion. Therefore, this experiment for the first time provides direct evidence that the Z → E isomerization is indeed electrocatalytic, as has been suggested in previous literature reports, , and as a result explains why direct measurement of the Z isomer’s cathodic peak potential using standard electrochemical techniques is not feasible. The fact, however, that the isomerization event occurs anodically shifted from where computation and our experiments with the locked Z azobenzene 3 suggesting that the cathodic peak potential of the Z isomer should occur can be explained with the aid of Nernst’s equation (eq ): According to this equation, the half-wave electrode potential ( E 1/2 ) of a given redox process (involving z electrons at a given temperature T ) depends on the standard potential ( E °) and the ratio of the activity coefficients of the two involved redox-active species ( a ox and a red ).…”

Section: Resultsmentioning

confidence: 99%

“…19 Photomodulated voltammetry (PMV) enabled Grampp and co-workers to distinguish the reduction potentials of the two azobenzene isomers, as they observed a cathodic shift of the reduction potential by −60 mV for the Z isomer in DMF. 20 The authors suggested that the use of PMV allowed for this observation as the technique is better suited to measure the potential of short-lived species and postulated that the Z azobenzene radical anion rapidly isomerizes to the corresponding E radical anion, resulting in only the E isomer potential being measured in conventional cyclovoltammetry (CV) experiments.…”

Section: ■ Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Electrocatalytic Z → E Isomerization of Azobenzenes

et al. 2016

View full text Add to dashboard Cite

A variety of azobenzenes were synthesized to study the behavior of their E and Z isomers upon electrochemical reduction. Our results show that the radical anion of the Z isomer is able to rapidly isomerize to the corresponding E configured counterpart with a dramatically enhanced rate as compared to the neutral species. Due to a subsequent electron transfer from the formed E radical anion to the neutral Z starting material the overall transformation is catalytic in electrons; i.e., a substoichiometric amount of reduced species can isomerize the entire mixture. This pathway greatly increases the efficiency of (photo)switching while also allowing one to reach photostationary state compositions that are not restricted to the spectral separation of the individual azobenzene isomers and their quantum yields. In addition, activating this radical isomerization pathway with photoelectron transfer agents allows us to override the intrinsic properties of an azobenzene species by triggering the reverse isomerization direction (Z → E) by the same wavelength of light, which normally triggers E → Z isomerization. The behavior we report appears to be general, implying that the metastable isomer of a photoswitch can be isomerized to the more stable one catalytically upon reduction, permitting the optimization of azobenzene switching in new as well as indirect ways.

show abstract

Section: ■ Conclusionsupporting

confidence: 89%

Section: Resultsmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Electrocatalytic Z → E Isomerization of Azobenzenes

et al. 2016

View full text Add to dashboard Cite

show abstract

“…The complexity and high line width of the spectra made its analysis somewhat difficult, but in 1991 Gerson and co-workers proved unequivocally by ENDOR spectroscopy that the coupling constants of the two ortho and the two meta hydrogen atoms in the phenyl groups are different, which implies restricted rotation around the nitrogen–phenyl bond . The reduction of either the cis or the trans isomer of azobenzene always yields the more stable trans radical, because the NN double bond is weaker in the radical than in the parent neutral molecule . Actually, the reduction of cis -azobenzene to its radical anion is considered to be responsible for the fast isomerization to the trans isomer, even by the effect of low electric fields in liquid crystals containing the azobenzene unit …”

Section: Introductionmentioning

confidence: 99%

Electronic Communication in Linear Oligo(azobenzene) Radical Anions

et al. 2013

View full text Add to dashboard Cite

The radical anions of five bis(azobenzene) and one tris(azobenzene) compounds were studied by optical and electron paramagnetic resonance (EPR) spectroscopies in polar aprotic solvents. The radicals with planar or almost-planar bridges are charge-delocalized mixed-valence species. Localization of charge occurs only on radicals with highly twisted biphenyl bridges. The electronic coupling between the azobenzene charge-bearing units, calculated as half the energy of the intervalence band for the charge-delocalized and by the Hush equation for the charge-localized radicals, decreases with the distance and torsion angle between azobenzene units. These radicals have smaller electronic couplings between charge-bearing units than other mixed-valence organic radicals with similar bridges. However, the application of a three-stage model to the tris(azobenzene) radical anion intervalence band yields an electronic coupling between consecutive azobenzenes that is higher than in any of the bis(azobenzene) radicals studied.

show abstract

“…The dropping of the cathodic current density due to the trans-to-cis photo-isomerisation of the azo-dye, that is, the absolute efficiency of the opto-electronic switch, Dj max , was quantified by subtracting the cathodic current density value at a constant reduction potential equal to E(O1/R1) before UV-irradiation, j 0 , from the one once the photo-stationary state has been reached, j irrad (Dj max = j irrad À j 0 ). The relative photo-electronic efficiency, Dj, which is independent of the scan rate but concentration-dependent, 21 was determined to be Dj = |(j irrad À j 0 )/j 0 | Â 100. All azopyridines showed notable changes in the cathodic current density upon UV-irradiation thereby showing absolute efficiencies ranging from 2.0 mA cm À2 to 5.4 mA cm À2 .…”

mentioning

confidence: 99%