Regioisomeric control of layered crystallinity in solution-processable organic semiconductors

Area of Science:

• Organic electronics
• Materials science
• Supramolecular chemistry

Background:

• 2D layered molecular packing is key for organic electronic materials.
• Controlling π-electron cores with functional substituents is essential.
• Benzothieno[3,2-b]naphtho[2,3-b]thiophene (BTNT) derivatives are promising semiconductors.

Purpose of the Study:

• Investigate regioisomeric structure-property relationships in mono-octyl-substituted BTNT (mono-C8-BTNT).
• Understand how peripheral octyl chain substitution affects molecular packing and electronic properties.
• Correlate crystal packing stability with thin-film transistor (TFT) performance.

Main Methods:

• Synthesized four positional isomers of mono-C8-BTNT.
• Analyzed molecular packing using X-ray crystallography.
• Calculated intermolecular interaction energies using dispersion-corrected DFT.
• Fabricated and characterized single-crystal TFT devices.

Main Results:

• Achieved isomorphous bilayer-type herringbone packing across all four mono-C8-BTNT isomers.
• Observed systematic variations in solubility and liquid-crystalline phase transitions with isomer substitution.
• Found higher crystal stability for 2- and 8-mono-C8-BTNT isomers due to ordered alkyl chain layers.
• Demonstrated high-performance TFT characteristics (mobility ~10 cm² V⁻¹ s⁻¹) for devices using 2- and 8-mono-C8-BTNT.

Conclusions:

• Peripheral substitution position significantly impacts crystal packing stability and electronic properties of mono-C8-BTNT.
• Optimized crystal packing, achieved through specific peripheral substitution, leads to high-performance organic semiconductors.
• This study provides a rational design strategy for developing advanced solution-processable organic electronic materials.