Solvent Effects on the Formation and Decay of Ionic Intermediates for the Photoreduction of Anthraquinone by Triethylamine in Ethanol, Toluene, and Acetonitrile at Room Temperature

Abstract

In toluene and ethanol containing triethylamine (TEA), a reaction of the lowest excited triplet state [3AQ(T1)] of anthraquinone (AQ) with ground-state TEA gave rise to the formation of an exciplex [3(AQ–TEA)*] which converted into a contact ion pair between the AQ radical anion (AQ−·) and the TEA radical cation (TEA+·). By an intramolecular proton transfer, this contact ion pair yielded anthrasemiquinone radical followed by the formation of 9,10-anthracenediol (AQH2); in ethanol, the monoanion (AQH−) of AQH2 was also produced. In ethanol/TEA, moreover, not only the decay rate constant of 3(AQ–TEA)* but also the quantum yield for the photoreduction of AQ were affected by the change of TEA concentration. This was interpreted in terms of the existence of a rapid interconversion between 3(AQ–TEA)* and atriplex [3(AQ–TEA2)*] of 3AQ(T1) with ground-state TEA. In contrast to the exciplex formation in ethanol and toluene, free AQ−· (and TEA+·) and 3(AQ–TEA)* [or a contact (or solvent-separated) ion pair between AQ−· and TEA+·] were produced in acetonitrile via the second and lowest excited triplet states of AQ, respectively: In the submicrosecond time regime, 3(AQ–TEA)* or the contact (or solvent-separated) ion pair dissociated into the radical ions (AQ−· and TEA+·) followed by their second-order reaction yielding finally AQH2 and AQH−.

Anthraquinone Photonucleases: Mechanisms for GG-Selective and Nonselective Cleavage of Double-Stranded DNA

“…(b) Photoreactions of 2AQA2(HEt 2 ) and 2AQC2(HEt 2 ) with Isopropyl Alcohol and Triethylamine. Anthraquinone derivatives having energetic nπ* excited states generally abstract a hydrogen atom from isopropyl alcohol to form ketyl radicals …”

Electrochemical Properties of Poly(l-2-anthraquinonylalanine)

“…After keeping the potential at −1.0 V for 15 min, the spectrum of the anthraquinone group disappeared and a new band appeared at 540 nm. The latter is assignable to the anthraquinone monoanion . When the voltage was set to −1.4 V, the spectrum of the monoanion appeared in the early stage (not shown in the figure), and after about 45 min the monoanion was converted to the dianion that shows a characteristic peak at 384 nm, as indicated by the dash−dotted line in Figure .…”

“…The latter is assignable to the anthraquinone monoanion . When the voltage was set to −1.4 V, the spectrum of the monoanion appeared in the early stage (not shown in the figure), and after about 45 min the monoanion was converted to the dianion that shows a characteristic peak at 384 nm, as indicated by the dash−dotted line in Figure . The observation of monoanions in the early stage has been interpreted in terms of intermolecular disproportionation between a dianion and a neutral anthraquinone to form two monoanions .…”

Production of Hydrogen Peroxide in Liquid CO2. 2. Catalytic Hydrogenation of CO2-philic Anthraquinones

“…Therefore, we chose to monitor the rate of hydrogenation by UV spectroscopy by following the disappearance of the FAQ peak. The same method was used previously to monitor the photoreduction of AQ derivatives. , In this way, we can measure the real concentration of FAQ in liquid CO 2 vs time without the need to calculate phase equilibrium data and without exposing the reaction system to air.…”

“…UV spectra recorded on-line exhibit isosbestic points (290 and 345 nm), demonstrating the quantitative conversion of the anthraquinone to the corresponding anthrahydroquinone (Figure ). The reaction was monitored by measuring the rate of disappearance of the absorption peak at 320 nm -1 , a peak that has been previously assigned to the anthraquinone block . Global rate constants ( k g ) were determined by fitting the experimental data ( c FAQ = f ( t )) with the exponential function given in eq 2b (Figure ).…”