Incorporation of pyrrole to oligothiophene-based quinoids endcapped with dicyanomethylene: a new class of solution processable n-channel organic semiconductors for air-stable organic field-effect transistors

Abstract

We report the synthesis and characterization of a novel series of pyrrole-containing quinoids endcapped with dicyanomethylene groups. The modification of the quinoidal core structure through incorporating pyrrole unit presents two main advantages: firstly, N-alkyl substituents of pyrrole can serve as solubilizing groups for the realization of solution-processability; secondly, the variation of N-alkyl substituents is easily achieved and thus greatly enriches the number of species in such a series of materials. Additionally, the retained quinoidal core structure as well as the electron-withdrawing endcapped group ensures a sufficiently low LUMO energy level (ca. 4.30–4.39 eV below the vacuum level), meeting the requirement for air-stable n-channel organic semiconductors. X-ray crystallographic data of 3b reveals that except for the branched alkyl substituent, the whole molecule shows high planarity by assuming a rarely observed syn conformation. Solution-processed OFETs based on such pyrrole-containing quinoids showed typical n-channel FET characteristics under ambient conditions, with a maximum electron mobility up to 0.014 cm² V⁻¹ s⁻¹ and I_on/I_off values of ca. 10⁴, indicating that this series of materials are promising candidates for solution processable n-channel semiconductors, and adopting a pyrrole moiety to the construct the quinoidal core structure provides an efficient approach to the development of novel n-channel organic semiconductors.