The crystal structures of the charge-transfer (CT) cocrystals formed by the π-electron acceptor 1,3,4,5,7,8-hexafluoro-11,11,12,12-tetracyanonaphtho-2,6-quinodimethane (F 6 TNAP) with the planar π-electron-donor molecules triphenylene (TP), benzo[b]benzo[4,5]thieno[2,3-d]thiophene (BTBT), benzo[1,2-b:4,5-b′]dithiophene (BDT), pyrene (PY), anthracene (ANT), and carbazole (CBZ) have been determined using single-crystal X-ray diffraction (SCXRD), along with those of two polymorphs of F 6 TNAP. All six cocrystals exhibit 1:1 donor/acceptor stoichiometry and adopt mixed-stacking motifs. Cocrystals based on BTBT and CBZ π-electron donor molecules exhibit brickwork packing, while the other four CT cocrystals show herringbone-type crystal packing. Infrared spectroscopy, molecular geometries determined by SCXRD, and electronic structure calculations indicate that the extent of ground-state CT in each cocrystal is small. Density functional theory calculations predict large conduction bandwidths and, consequently, low effective masses for electrons for all six CT cocrystals, while the TP-, BDT-, and PYbased cocrystals are also predicted to have large valence bandwidths and low effective masses for holes. Charge-carrier mobility values are obtained from space-charge limited current (SCLC) measurements and field-effect transistor measurements, with values exceeding 1 cm 2 V −1 s −1 being estimated from SCLC measurements for BTBT:F 6 TNAP and CBZ:F 6 TNAP cocrystals. exhibit properties distinct from those of their individual components. In chargetransfer (CT) cocrystals, one component acts as an π-electron donor (D) and another component acts as a π-electron acceptor (A), and both are typically planar molecules in order to facilitate CT interactions in the solid state. Two major types of molecular stacking motifs are found in CT crystals with 1:1 stoichiometry: mixed stacks, in which D and A molecules alternate along the stacking direction, -D-A-D-A, and segregated stacks, in which donor and acceptor molecules form separate stacks, -D-D-D-and -A-A-A. [1][2][3] When free of disorder, metallic conductivities can be obtained along the stacking direction of CT cocrystals that form segregated stacks and that exhibit extents of CT approximately midway (ρ = ca. 0.5) between the completely neutral (ρ = 0) and fully ionic (ρ = 1) limits. [1][2][3][4] On the other hand, CT cocrystals that consist of mixed stacks generally behave as semiconductors or insulators. [3,5] Recently there has been increasing interest in the semiconducting [6][7][8][9][10][11][12][13][14][15][16][17][18] and photoconductive [19][20][21] properties of mixed-stack cocrystals. Large charge-carrier mobility values, µ, have been reported for several examples using space-charge limited current (SCLC) or field-effect transistor (FET) measurements, includingThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.
