| UV–Vis absorption spectroscopy | Sharp, well-defined absorption maxima at 630 nm and 700 nm, accompanied by a broader band centered at 490 nm |
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| Photoluminescence | No photoluminescence was detected upon excitation |
| Fluorescence spectroelectrochemistry | An emission spectrum was observed only with excitation at 370 nm and assigned to the neutral species; the spectrum was the specular image of the absorption spectrum; no emission bands were observed with excitation at 500, 640, or 700 nm |
Daniel Morales-Martinez, Stefano Visentini, Lopa Paul, Lorenzo Rizzo, Agostino Migliore, Sara Bonacchi, Luca Dell’Amico. “An in-situ electrophotochemical generated hydrogen-bonded complex drives the catalytic activation of carbon-halogen bonds.” ChemRxiv (). https://doi.org/10.26434/chemrxiv.15007815/v1
| Cyclic voltammetry | Two chemically reversible peaks associated with DCA•⁻ (EIa/Ic vs SCE = −0.92 V) and DCA²⁻ (EIIa/IIc vs SCE = −1.62 V) |
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| Cyclic voltammetry at the first reduction peak (0.05 to 50 V s⁻¹) | No additional peaks; DCA•⁻ was chemically reversible during the cyclic-voltammetry timescale (t < 2 min) |
| Cyclic-voltammetry scan-rate variation | Normalized peak current increased at high scan rates |
| Cyclic voltammetry after addition of 18 equivalents of water | Peak IIIa increased; peak IIa lost chemical reversibility, related to consumption of DCA²⁻ |
| Cyclic voltammetry after oxygen bubbling | Peak IIIa was not observed |
| Cyclic voltammetry, DCA²⁻ | Formation was sensitive to the presence or absence of water in the medium |
| Potentiostatic coulometry (Eapplied vs SCE = −1.02 V) | Approximately two electrons per DCA molecule were consumed |
| Appearance after electrolysis | Distinct deep-purple solution, in contrast to the characteristic red solution observed under strictly anhydrous conditions |
| Cyclic voltammetry | Progressive attenuation of the reversible DCA/DCA•⁻ redox couple, concurrently with the emergence of two prominent irreversible oxidation features at more anodic potentials |
| UV–Vis absorption spectroscopy during electrolysis | Structured DCA absorption bands (350–450 nm) were systematically depleted and replaced by broad, complex electronic transitions extending from 300 to 650 nm |
| UV–Vis absorption spectroscopy (24 h in the dark without an applied potential) | Well-defined absorption maxima at 450, 480, and 510 nm |
| UV–Vis absorption spectroscopy after exposure to air | Disappearance of the bands at high wavelengths (550 and 600 nm) was instantaneous |
| Operando UV–Vis spectroelectrochemistry after exposure to air | Rapid transition from purple to dark orange as Species Y was consumed, while the absorption bands of Species X remained stable |
| Operando UV–Vis spectroelectrochemistry, DCA•⁻ | Maximum concentration at approximately 400 s |
| Operando UV–Vis spectroelectrochemistry, Species Y | λmax = 595 nm; began to accumulate after 120 s |
| Operando UV–Vis spectroelectrochemistry, Species X | λmax = 510 nm; near-linear accumulation throughout the electrolysis period |
| UV–Vis spectroelectrochemistry (benzene/acetonitrile 1:1) | After 30 minutes, the main product was still the radical anion of DCA and only traces of Species Y were observed; the band at 705 nm showed progressive growth |
| Fluorescence spectroscopy, stable orange mixture | Emission maxima at 533, 563, and 605 nm |
| UV–Vis absorption spectroscopy and cyclic voltammetry, electrolysis at DCA’s second peak under argon | Species X formed; peaks and bands were identical to those observed at the first peak; formation of the same species observed previously; image data were not transcribed |
| ¹H NMR spectrum after extraction with toluene | Image data were not transcribed; 9,10-anthraquinone (AQ) was the main product, and other products were also observed |
| UV–Vis spectroelectrochemistry and cyclic-voltammetry plots | Image data were not transcribed |
| UV–Vis absorption spectroscopy, AQ•⁻ in rigorously anhydrous acetonitrile | Broad near-infrared absorption band centered at ~900 nm |
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| UV–Vis absorption spectroscopy during AQ electrosynthesis | Quick formation of Species X was observed |
| UV–Vis absorption spectroscopy during oxygen diffusion | The AQ•⁻ near-infrared band progressively decreased, while new UV–Vis bands appeared between 450 and 550 nm |
| UV–Vis spectroelectrochemistry, solvent-water comparison | Water traces favored the formation of Species X, whereas only the formation of the radical anion of anthraquinone was observed in dried acetonitrile |
| UV–Vis spectroelectrochemistry, electrolysis at the second peak in acetonitrile 99.8 % | The evolution of the spectrum during electrolysis evidenced the formation of the radical anion |
| UV–Vis spectroelectrochemistry, electrolysis at the second peak in open air | The evolution of the spectrum during electrolysis only showed the formation of Species X and an additional band at 600 nm |
| UV–Vis absorption spectroscopy, final AQ-derived and DCA-derived products | The spectra matched; λmax values differ by <5 nm, relative peak intensities are nearly identical, and fine spectral features are preserved |
| Cyclic voltammetry, final AQ-derived and DCA-derived products | Identical electrochemical signatures, with the same irreversible oxidation peak at Ep vs SCE ≈ 0.2 V |
| ¹H, ¹³C, COSY and HSQC NMR spectra | Image data were not transcribed |
| COSY NMR, extracted product | Additional signals are correlated with each other, meaning that they are related to the same species |
| HSQC NMR, extracted product | Correlation of the aromatic protons with the corresponding aromatic carbons was detected |
| ¹H and ¹³C NMR, extracted product | 3 aromatic protons, 8 aromatic carbons, and 1 phenol-type proton |
| ¹H NMR, Species X after column chromatography | 4 aromatic protons and 1 phenolic proton; the product evolved quickly to AQ; image data were not transcribed |
| ¹H NMR stability series (0, 15, 30 and 72 h) | Signals associated with Species X tended to disappear, whereas the bands of AQ grew; the Species X signal was at δ = 8.58 ppm and the AQ signal was at δ = 8.35 ppm; image data were not transcribed |
| UV–Vis and ¹H NMR stability under commercial lamps | Species X was not stable in the presence of light, and AQ regenerated over time; image data were not transcribed |
| UV–Vis absorption spectroscopy under 450 nm irradiation | Under argon, traces of Species X remained after 120 min; in the presence of oxygen, complete consumption of Species X was observed after 30 min; image data were not transcribed |
| UV–Vis absorption spectroscopy after 456 nm irradiation | The absorption profile showed formation of the dimeric complex over time during electrolysis; after 456 nm irradiation, its absorption bands disappeared over time; image data were not transcribed |
| KI colorimetric test for H₂O₂ | The blank solution showed no color change, while the irradiated solution turned orange-brownish, indicating H₂O₂; the figure caption describes the mixtures as colorless and yellow, respectively |
| NMR assignment | From preliminary results of one-dimensional and bi-dimensional NMR experiments (¹H, ¹³C, COSY, and HSQC), the compound X structure was proposed as a reduced mono-protonated AQ |
| Control experiment in the presence of benzene | Sole formation of the monomer |
| UV–Vis, fluorescence and electrochemical plots | Image data were not transcribed |