Direct observation of electron transfer in solids through X-ray crystallography

Nanoscale electron transfer (ET) in solids is fundamental to the design of multifunctional nanomaterials, yet its process is not fully understood. Herein, through X-ray crystallography, we directly observe solid-state ET via a crystal-to-crystal process. We first demonstrate the creation of a robust and flexible electron acceptor/acceptor (A/A) double-wall nanotube crystal ([(Zn²⁺)₄(L_A)₄(L_A=O)₄]_n) with a large window (0.90 nm × 0.92 nm) through the one-dimensional porous crystallization of heteroleptic Zn₄ metallocycles ((Zn²⁺)₄(L_A)₄(L_A=O)₄) with two different acceptor ligands (2,7-bis((1-ethyl-1H-imidazol-2-yl)ethynyl)acridine (L_A) and 2,7-bis((1-ethyl-1H-imidazol-2-yl)ethynyl)acridin-9(10H)-one (L_A=O)) in a slow-oxidation-associated crystallization procedure. We then achieve the bottom-up construction of the electron donor incorporated-A/A nanotube crystal ([(D)₂⊂(Zn²⁺)₄(L_A)₄(L_A=O)₄]_n) through the subsequent absorption of electron donor guests (D = tetrathiafulvalene (TTF) and ferrocene (Fc)). Finally, we remove electrons from the electron donor guests inside the nanotube crystal through facile ET in the solid state to accumulate holes inside the nanotube crystal ([(D^•+)₂⊂(Zn²⁺)₄(L_A)₄(L_A=O)₄]_n), where the solid-state ET process (D - e^- → D^•+) is thus observed directly by X-ray crystallography.