Incorporating Spacer Molecules into the Tetrathiafulvalene–p‑Chloranil Charge-Transfer Framework: Modulating the Neutral–Ionic Phase Transition

The charge-transfer (CT) tetrathiafulvalene–p-chloranil (TTF–CA) crystal, a representative functional organic electronic material, has been the subject of both basic and applied research. This material shows a neutral–ionic phase transition (NIPT) that induces drastic changes in its physical properties. Here, we use this crystal as a framework and demonstrate a method for modulating physical properties of TTF–CA. A number of multicomponent (ternary) CT crystals were obtained by crystallizing TTF–CA with a third molecular species. These complexes all contain molecular sheets formed with TTF–CA; however, the third molecules were differently inserted between these sheets as spacers to induce a variety of physical properties in the CT crystals. Some showed spacer-modified NIPT, while the transition to the ionic state was suppressed in one complex despite the presence of TTF–CA sheets, which indicates that spacer molecules can modulate the physical properties or functions of CT crystals.