Fig. 3: Reference compounds, (spectro-)electrochemistry and transient absorption spectroscopy.
From: Photoinduced double charge accumulation in a molecular compound
a, Reference molecules of the individual redox-active units of the triad and the pentad. b, Cyclic voltammograms of the first reduction of the reference electron acceptors ref-AQ (orange) and ref-NDI (red) along with the first oxidation of the reference electron donors ref-TAA (blue) and ref-PTZ (green) (top) and cyclic voltammogram of the main ligand of the pentad (with all organic redox-active units present but no Ru(II) coordinated) showing the same redox events and additionally the reduction of NDI•− to NDI2− (bottom). The dotted vertical lines indicate the midpoint between the peak potentials in the oxidative and reductive sweeps, respectively. c, Difference UV–vis absorption spectra obtained after electrochemical oxidation of ref-PTZ to ref-PTZ•+ (green) and after reducing ref-AQ to ref-AQ•− (orange). d, Difference spectra obtained after electrochemical oxidation of ref-TAA to ref-TAA•+ (blue) and after reducing ref-NDI to ref-NDI•− (red). The dashed black trace is the linear combination of the two spectra using a scaling factor to take the different extinction coefficients of the ref-TAA•+ and ref-NDI•− radicals into account. The resulting sum spectrum is the expected UV–vis absorption signature of the CSS-2 in Fig. 2d (D2•+–D1–PS–A1–A2•−). e, UV–vis transient absorption spectra of the pentad in dry Ar-saturated CH3CN at 20 °C after excitation with 460 nm laser pulses (approximately 17 mJ) of approximately 10 ns duration, time-integrated for 200 ns after the indicated delay times (purple traces). The expected sum spectrum from d (black dashed trace) is included for direct comparison. The asterisk marks the signature of TAA•+ (see text for details).
