Linker dependent symmetry breaking charge separation in 9,10-bis(phenylethynyl)anthracene dimers

Abstract

To develop new efficient symmetry breaking charge separation (SB-CS) materials with fast rate and slow recombination in nonpolar or weakly polar solvents is urgent for its better practical application, yet it remains a great challenge. Herein, we synthesized three 9,10-bis(phenylethynyl)anthracene dimers linked by a phenylene spacer in an ortho- (o-dimer), meta- (m-dimer), and para- arrangement (p-dimer), in which the electronic coupling between the two BPEA units could be tuned by changing their relative orientation. Their SB-CS properties were investigated comparatively using steady-state/transient absorption and fluorescence spectroscopy. The result shows that fast SB-CS could be conducted in o-dimer even in weakly polar solvents. However, the slow SB-CS process is only carried out in polar solvents for the m-dimer. Furthermore, the SB-CS state could be stable for several nanoseconds for o-dimer and m-dimer. In the same solvent, p-dimer has the fastest SB-CS rate compared to o-dimer and m-dimer, but the recombination rate is also the fastest. Different SB-CS dynamics in these three dimers should be caused by their different electronic coupling strengths induced by various molecular orientations. The fast SB-CS and slow recombination of o-dimer in weakly polar solvents make it a highly promising material for application in optoelectronic technologies. The SB-CS process cannot proceed in polystyrene film for these three dimers, suggesting that molecular rotation plays an important role in the SB-CS process except the electronic coupling. This work provides some insights into developing novel SB-CS materials for practical applications.