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Abstract 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 (F6TNAP) 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 F6TNAP. 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 PY‐based 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 cm2V−1s1being estimated from SCLC measurements for BTBT:F6TNAP and CBZ:F6TNAP cocrystals.
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This content will become publicly available on November 20, 2026
Charge Transport in Ternary Charge‐Transfer Solid Solution Single Crystals
Abstract The electronic effects of structural defects introduced through chemical doping are challenging to characterize in organic semiconductors, especially when measured in thin film devices where the performance is sensitive to structural heterogeneity. Here, a simple approach is presented to probe the roles of indirect and direct electronic coupling on charge transport in a series of compositionally varied charge‐transfer single crystals. In this system, carbazole (CBZ) is controllably substituted withN‐methylcarbazole (NMCBZ) in the cocrystal formed between CBZ and 1,3,4,5,7,8‐hexafluoro‐11,11,12,12‐tetracyano‐2,6‐naphthoquinodimethane (F6TNAP), producing a series of single crystals with compositions that range between 0 – 50% CBZ replacement and preserve the structure type of the parent cocrystal. Gas‐phase electronic structure calculations predict that substitutional replacement of CBZ with NMCBZ introduces two competing effects: (i) strengthening of indirect coupling by increasing the average degree of charge transfer and (ii) weakening of direct exchange by increasing the distance between adjacent charge‐transfer π‐stacks. Charge transport measurements reveal an initial decrease in the mobility upon substitution of CBZ with NMCBZ, rationalized by a combination of hole‐trapping and weakened direct coupling with increasing NMCBZ content. Critically, these results demonstrate the potential for solid solutions to offer insight into charge transport mechanisms and their chemical tunability in molecular electronic materials.
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- PAR ID:
- 10660181
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Advanced Functional Materials
- ISSN:
- 1616-301X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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