Layered‐Herringbone Polymorphs and Alkyl‐Chain Ordering in Molecular Bilayer Organic Semiconductors

Abstract

Production and control of two-dimensionally self-organized layers of π-conjugated molecules is the fundamental issue in organic electronics devices. This study reports that an intralayer polymorphic transformation is apparently observed in a bilayer-type layered-herringbone packing of a series of 2mono-alkylated-benzothieno [3,2-b][1]benzothiophenes (mono-C n -BTBTs) with the change in the substituted alkyl-chain length, n. Slight variation in the intermolecular arrangement in the single-crystal films is investigated with reasonable sensitivity via polarized optical absorption spectroscopy through the excitonic interactions between neighboring π-electron cores. A clear polymorphic transition is observed based on the features of the in-plane optical anisotropy with the change in the chain length between n = 7 (or less) and 8 (or more). A unique phase separation of the polymorphs is also observed in the films produced using a mixed solution with molecules having different n: the respective polymorphic phases appear separately, either as single molecular bilayers or multi-bilayer-stacked films owing to geometrical frustration. The results indicate that the intralayer packing motif is predetermined by the competition and balance between the intermolecular core-core and chain-chain interactions. These findings pave the way for rational designing of organic molecules with considerably high layered crystallinity, and thus, of efficient carrier transport in organic thin-film transistors. (200 words)Received: ((will be filled in by the editorial staff))Revised: ((will be filled in by the editorial staff))

Synthetic Bilayers on Mica from Self-Assembly of Hydrogen-Bonded Triazines

“…In a related study, thin films of alkyl-substituted benzothiophenes were observed to undergo polymorphic transitions when the alkyl chains increase from C7 to C8, and distinct phases occurred in mixtures of these compounds due to geometric frustration. 12 Studies on solution-cast organic thin films are typically limited to specific compounds known to act as functional materials. However, these compounds usually provide limited opportunities to functionalize their molecular structure to optimize the resulting thin film.…”

“…The resulting geometrical frustration from the alkyl chains suppressed interlayer stacking. In a related study, thin films of alkyl-substituted benzothiophenes were observed to undergo polymorphic transitions when the alkyl chains increase from C7 to C8, and distinct phases occurred in mixtures of these compounds due to geometric frustration . Studies on solution-cast organic thin films are typically limited to specific compounds known to act as functional materials.…”

Graphene‐Quantum‐Dots‐Induced Centimeter‐Sized Growth of Monolayer Organic Crystals for High‐Performance Transistors

“…This indicates that the monolayer C 10 ‐BTBT crystal has a well‐aligned molecular orientation in a – b plane. [ 35 ] These above results collectively demonstrate that monolayer C 10 ‐BTBT crystals with high crystallinity are obtained by using the GQDs‐induced self‐assembly method.…”

Effects of Thiophene-Fused Isomer on High-Layered Crystallinity in π-Extended and Alkylated Organic Semiconductors

“…It is found that the π-core of synC6 is slightly bent and thus is not suitable for close and uniform antiparallel molecular arrangement in the hypothetical aai -HB lattice. Finally, we investigated the intermolecular C–H···π distance in the T -shaped arrangements (Figure and Table S4), as the fundamental unit for the HB packing. , We found that the H···π distances between the C–H terminals and the contacting π-electron plane are mostly shorter in the actual lattice than in the hypothetical lattice for both the isomers. These results corroborate that the actual lattices should be selectively formed by tighter HB packing.…”