Reversible Symmetry-Breaking Charge Separation in a Series of Perylenediimide Cyclophanes
journal contributionposted on 07.05.2020, 08:52 by Adam F. Coleman, Michelle Chen, Jiawang Zhou, Jae Yoon Shin, Yilei Wu, Ryan M. Young, Michael R. Wasielewski
Excited-state symmetry-breaking charge separation (SB-CS) can offer an efficient pathway to solar energy capture and conversion. We synthesized a series of 1,6,7,12-tetrakis(4-t-butylphenoxy)perylene(3,4:9,10)bis(dicarboximide) cyclophane dimers with m-xylylene, p-xylylene, and 4,4′-diyldimethane-1,1′-biphenyl spacers and studied them with steady-state and time-resolved optical spectroscopies. Photoinduced SB-CS occurs in all three cyclophanes in CH2Cl2, with the SB-CS rate decreasing as the interchromophore distance is increased. Time-resolved emission spectroscopy and kinetic modeling reveal that the charge-separated state exists in pseudoequilibrium with the excited state prior to decay. Notably, the meta-spaced cyclophane also undergoes SB-CS in toluene within ∼100 ps, despite the lack of charge stabilization by the low dielectric constant solvent. These results demonstrate that SB-CS can occur across long distances and in weakly polar environments, which offers the possibility of harnessing SB-CS for solar energy capture and conversion.