Ni-Mediated Cascade Synthesis of a Vinylene-Linked Terrylene Diimide Dimer with Symmetry-Breaking Charge Separation Character

Despite remarkable progress in the field of metal-mediated cascade reactions over the past few decades, the inherent complexity of multiple metal-coupled steps continues to pose significant challenges in mechanistic elucidation and reaction pathway control. Herein, we achieve precise control of a Ni-mediated cascade reaction by tuning the stoichiometry ratio of substrate chloroform and dichlorinated terrylene diimides (2Cl-TDI). Mechanistic studies show a small amount of chloroform promotes the formation of five-membered cyclic intermediate, yielding intermolecular coupling product vinylene-linked terrylene diimide dimer (FV-TDI), while excess chloroform favors six-membered cyclic intermediate and forming intramolecular coupling product Ch-TDI. This is the first example of Ni-mediated cascade reactions directly contructing aromatic frameworks from C(sp³) sources. UV-Vis absorption confirms FV-TDI as a strong exciton-coupled dimer. Unexpectedly, fs-TA reveals FV-TDI undergoes symmetry-breaking charge separation (SB-CS) in both solution and thin-films. Similar to FV-TDI, its structural homologue FV-PDI (vinylene-linked perylene diimide dimer) also exhibits SB-CS, as confirmed by fs-TA spectroscopy. This shows that vinylene-linked dimers likely represent a general molecular design strategy of strong exciton-coupled SB-CS systems. To our best knowledge, this represents the first example of SB-CS in strong exciton-coupled organic thin-films, offering valuable insights for developing high-efficiency organic optoelectronic devices with near-zero exciton dissociation energy loss.