Effects of alkyl chain on the liquid crystalline properties of [1]benzothieno [3,2-b][1]benzothiophene-based organic semiconductors

초록

New [1]benzothieno[3,2-b] [1]benzothiophene (BTBT)-based small molecules with different substituents were synthesized and employed as solution-processable organic semiconductors for organic thin-film transistors (OTFTs). Two types of alkyl side chains (octyl/ethylhexyl) were selected for the solubility enhancement and analysis of material phase transition. Thermal, optical, and electrical properties of new compounds were analyzed and characterized. Synthesized BTBT derivatives exhibited completely different phase transition features depending on the attached side chains; linearly alkylated 2-octyl-7-(5-octylthiophen-2-yl)benzo[b]benzo [4,5]thieno[2,3-d]thiophene (compound 1) showed decent carrier mobility up to 0.26 cm2/Vs at highly ordered smectic X phase, while 2-(5-(2-ethylhexyl)thiophen-2-yl)-7-octylbenzo[b]benzo [4,5]thieno[2,3-d]thiophene (compound 2) with branched alkyl chain showed poor electrical performance. Thin film morphology and microstructure were investigated using atomic force microscopy and X-ray diffraction to reveal the dramatic property difference between the two dialkylated BTBT derivatives.

키워드