Knitting up 2,7-disubstituted carbazole based oligomers through supramolecular interactions for their application in organic thin film transistors

Abstract

For the design and development of organic electronic devices, the main focus is particularly on the synthesis of new organic semiconductors and dielectric materials. Molecular engineering is another effective strategy, in this direction which has been explored successfully in this study through synthesis of a π-conjugated oligomer CbzTPAU2, with M_w = 2169. This bow shaped oligomer has its core unit made of 2,7-disubstituted carbazole which further has been connected to its end-terminal unit TPAU2 by 1,4-bis(decyloxy)-2,5-diethynylbenzene. The presence of a uracil moiety on end terminals of CbzTPAU2 has triggered the self-assembly of CbzTPAU2 molecules through knitting up of each of these single units through four Uracil–Uracil intermolecular hydrogen bonds (U⋯U) per CbzTPAU2 unit. An Atomic Force Microscope (AFM) study was employed to explore the directionality of hydrogen bonding. Further, the effect of solvent polarity on the stability of U⋯U bonding in CbzTPAU2 oligomers has also been reported here in this study. The potential of these self-assembled CbzTPAU2 oligomers when explored as charge transporting layers in OTFTs has shown p-type behaviour. The OTFT device bottom-gate, top-contact when fabricated on the heavily doped n-type Si wafer with SiO₂ as a gate dielectric (200 nm) has shown a good on/off ratio 3.43 × 10³ and with an average hole mobility of 0.167 cm² V⁻¹ s⁻¹.