Thiophene-S,S-dioxidized indophenines as high performance n-type organic semiconductors for thin film transistors

Abstract

The synthesis of three new isomerically pure (E,E,E)-form thiophene-S,S-dioxidized indophenine (IDTO) compounds, (3Z,3′Z)-3,3′-((E)-1,1,1′,1′-tetraoxido-5H,5′H-[2,2′-bithiophenylidene]-5,5′-diylidene)bis(1-dodecyl-indolin-2-one) (4a-S1), (3Z,3′Z)-3,3′-((E)-1,1,1′,1′-tetraoxido-5H,5′H-[2,2′-bithiophenylidene]-5,5′-diylidene)bis(5-bromo-1-dodecyl-indolin-2-one) (4b-S1) and (3Z,3′Z)-3,3′-((E)-1,1,1′,1′-tetraoxido-5H,5′H-[2,2′-bithiophenyldene]-5,5′-diylidene)bis(6-bromo-1-dodecyl-indolin-2-one) (4c-S1), and their use as n-channel semiconductors for organic thin film transistors (OTFTs) are reported. Compared to the non-oxidized parent indophenine compound 3,3′-(5H,5′H-[2,2′-bithiophenylidene]-5,5′-diylidene)bis(1-dodecylindolin-2-one) (3a), 4a-S1 exhibited significantly lower HOMO and LUMO energy levels. Having bromine atoms at the 5,5′- (4b-S1) or 6,6′-positions (4c-S1), the HOMO and LUMO energy levels further decreased. In OTFT devices, these IDTO compounds exhibit unipolar n-type semiconductor behavior due to their significantly deeper LUMO and HOMO energy levels than those of 3a that shows ambipolar charge transport performance. The maximum electron mobilities of 4a-S1, 4b-S1 and 4c-S1 are in the order of 10⁻² to 10⁻¹ cm² V⁻¹ s⁻¹, which are much higher than that of 3a (∼10⁻³ cm² V⁻¹ s⁻¹), originating from the lower LUMO energy levels and the high isomeric purities of the former compounds. Among the three IDTO compounds, 4c-S1 shows the highest electron mobility of up to 0.11 cm² V⁻¹ s⁻¹, which is likely due to its most extended π-electron delocalization on the LUMO wavefunction.