Figure 1

Donor-acceptor dyads $\mathbf{1}$ and $\mathbf{2}$ consisting of perylenediimide (PDI) and terrylenediimide (TDI) linked by oligo(phenylene) bridges. In the inset the relevant processes upon photoexcitation are depicted. Excitation of PDI leads to electronic energy transfer to TDI (EET) and acceptor fluorescence. If both chromophores are in the first excited singlet state ($S_1$), in principal donor fluorescence as well as singlet-singlet annihilation (SSA) could occur.Reuse & Permissions

Figure 2

(a) The confocal SMS setup. OL: objective lens, Exc: excitation light, DC: dichroic mirror, BS: 50:50 beam splitter, F: filter, Spectr: spectrograph, APD: avalanche photodiode. (b) Instrumental response functions of the three excitation sequences. During sequence $A$ the molecules were excited by the green laser (523 or 520 nm) only. During sequence $B$ and $C$ we excited with red (635 nm) and green laser pulses and different time delays $\Delta t_1=12.5\mathrm{ns}$ and $\Delta t_2=-0.7\mathrm{ns}$, respectively.Reuse & Permissions

Figure 3

(a) The excitation cycle monitored from reflected excitation light of both lasers. $A$, $B$, and $C$ correspond to the excitation sequences displayed in Fig. 2b. The fluorescence time traces (b)–(d) match the excitation cycle depicted in (a). (b) Fluorescence time trace of a single TDI molecule. (c) Section of an experimental time trace of dyad $\mathbf{1}$. The emission at the TDI channel (red) showed a strong dependence on the excitation scenario. During pulse sequence $C$, the intensity decreased significantly compared to scenario $B$ because of efficient SSA ($>86\%$). The PDI channel (green, magnified 10 times) detected no fluorescence at any time. At $\sim 9.1\mathrm{s}$ the donor chromophore underwent photobleaching. (d) Section of an experimental time trace of dyad $\mathbf{2}$. A small but constant amount of PDI fluorescence (magnified 10 times) was detected in this case.Reuse & Permissions