Photoinduced asymmetric charge trapping in a symmetric tetraazapyrene-fused bis(tetrathiafulvalene) conjugate

In fused donor-acceptor (D-A) ensembles, rapid charge recombination often occurs because the D and A units are spatially close and strongly coupled. To the best of our knowledge, a long-lived charge separated (CS) state is still elusive in such systems. The results presented here show that symmetric annulation of two tetrathiafulvalene (TTF) donors to a central tetraazapyrene (TAP) acceptor via two quinoxaline units leads to a CS state lifetime of a few ns. A detailed study of the electronic interactions between TTF and TAP units in the ground and excited states was performed and compared with the asymmetric counterpart by cyclic voltammetry, optical absorption and ultrafast transient absorption spectroscopy. The results demonstrate that the photoinduced asymmetric charge trapping between two TTFs significantly stabilizes the CS state, which is also verified theoretically. Asymmetric charge trapping in a symmetric TTF-TAP-TTF leads to a significant stabilization of the charge-separated state of a few ns, which contrasts strongly with the asymmetric TAP-TTF where rapid charge recombination occurs within 2 ps.

Automated summary

This study demonstrates that long-lived charge-separated (CS) state can be achieved in fused donor-acceptor ensembles through symmetric annulation. Asymmetric charge trapping significantly stabilizes the CS state and leads to a longer lifetime compared to asymmetric systems.