From Anthracene Dimer to Trimer: Accelerated Symmetry-Breaking Charge Transfer and Suppressed Charge Recombination

Symmetry-breaking charge separation (SB-CS) shows enormous potential applications in solar energy conversion. Nonetheless, the realization of fast CS coupled with slow charge recombination (CR), which is crucial to achieving its application, remains a great challenge. To address this challenge, we have synthesized an anthracene dimer and a trimer by increasing the number of structural units to achieve fast generation and slow recombination of the SB-CS state. Transient absorption spectra show that these two oligomers could undergo the SB-CS process, even in low-polarity solvents. In the same solvent, the SB-CS rate of the trimer is 1.5-fold faster than that of the dimer, while its recombination rate is slowed down (from 1/17 ns^-1 to 1/20 ns^-1). The rate ratio between SB-CS formation and recombination in biph-trimer reaches an impressive ∼4000 in DMF, which is the highest record observed in the anthracene derivative system. These results suggest that increasing the structural unit number in oligomers may be an effective method to achieve fast SB-CS and slow CR.