Fig. 5: Observation of the different charge-separated states.
From: Photoinduced double charge accumulation in a molecular compound
a, Transient absorption spectra of the CSS-2 in the pentad and the CSS in the triad. The CSS of the triad is composed of PTZ•+ and AQ•− and serves as a spectroscopic reference for the CSS-1 and CSS-3 in the pentad. The spectra were time-integrated over the first 200 ns after the excitation of a 20 µM solution of the pentad or a 16 µM solution of the triad in dry, Ar-saturated CH3CN. Laser pulses of approximately 10 ns duration at 460 nm were used. b, Transient absorption spectra of a 300 µM solution of the pentad in dry dimethylformamide after excitation with 460 nm pulses of approximately 250 fs duration. The CSS-1 can be observed from 5 to 100 ps, after which the spectroscopic signatures spontaneously evolve into those of CSS-2. c, Transient absorption spectra recorded as described in b while the solution is continuously irradiated with an external cw laser of 447 nm. The spectroscopic signature of this CSS-3 is similar to the one of CSS-1 but cannot evolve any further, because TAA•+ cannot be further oxidized by PTZ•+ and NDI•− cannot be further reduced by AQ•−. d, Schematic representation of the photoproducts on the µs timescale after single excitation of the triad (CSS) and the pentad (CSS-2) as observed in a. e, Schematic representation of the photoproducts observed on the sub-nanosecond timescale in the pump–probe (b, purple) and the cw-pump–pump–probe (c, green) experiments.
