Synthesis, Ensemble, and Single Molecule Characterization of a Diphenyl-Acetylene Linked Terrylenediimide Dimer

The synthesis and the photophysical characterization at the ensemble and single molecule level of a terrylenediimide (TDI) dimer are reported. The spectroscopic experimental data are compared with those obtained for the corresponding model compound TDI. Steady-state and ps time-correlated single photon counting have shown that both chromophores in the TDI dimer are in the weak coupling regime allowing their interaction by Förster resonance energy transfer. Femtosecond transient absorption experiments showed an excitation power dependence of the fluorescence decay, which could indicate the occurrence of singlet-singlet annihilation. Single molecule intensity traces were investigated for the TDI dimer and suggested two intensity levels. For both intensity levels several parameters among which emission maximum, fluorescence decay times, antibunching, blinking off-times and rate of dark state formation were compared. The blinking analysis revealed that the yield of dark state formation is an order of magnitude higher when the two chromophores are still active compared to the case where one is photobleached. The off-times remain however similar.