Self-assembled monolayers made of 6-(5-((6-((5-hexylthiophen-2-yl)ethynyl)- 9,10-bis(phenylethynyl)anthracen-2-yl)ethynyl)thiophen-2-yl)hexyl 3-(triethoxysilyl)propylcarbamate for ultrathin film transistors

A new functionalized triethoxysilane bearing an X-shaped, anthracene-based semiconducting molecule on one arm was designed and synthesized as a precursor for the preparation of a self-assembled monolayer (SAM) on a SiO₂ substrate. 3-Isocyanatopropyl triethoxysilane was reacted with a monohydroxyl-terminated X-shaped, anthracene-based semiconducting molecule in the presence of tin catalyst. The 6-(5-((6-((5-hexylthiophen-2-yl)ethynyl)-9,10- bis(phenylethynyl)anthracen-2-yl)ethynyl)thiophen-2-yl)hexyl 3-(triethoxysilyl)propylcarbamate (BATHT-TEOS) was found to be stable and sufficiently reactive to form organic monolayers on hydroxylated SiO₂ surfaces. The structures and properties of these SAMs were investigated using X-ray photoelectron spectroscopy, UV-vis absorption spectroscopy, photoluminescence (PL) spectroscopy, laser scanning confocal microscopy-PL spectrometry, and spectroscopic ellipsometry. In this work, BATHT-SAM was employed as an interfacial layer on SiO₂ to fabricate ultrathin film transistors (UTFTs, active layer thickness ∼ 16.09 nm). The device UTFT-I, made of 0.06 wt % 5,5'-(9,10-bis(phenylethynyl)anthracene-2,6-diyl)bis(ethyne-2, 1-diyl)bis(2-hexylthiophene) (BATHT) solution on an n-octyltrichlorosilane-SAM/ SiO₂ layer, showed no gate effect for the carrier transport behavior; however, the device UTFT-II, fabricated on BATHT-SAM/SiO₂, exhibited field effect mobilities of 0.04 cm² V^-1 s^-1 (I_on/off ∼ 6.3*- 10³ to 1.0*- 10 ⁴). This can be attributed to the effect of BATHT-SAM inducing uniform coverage and ordering of BATHT molecules as an upper layer.