Small molecules based on strongly electron-deficient aza-isatinylidene malononitrile for solution-processed n-type field-effect transistors

Abstract

In this paper, three donor–acceptor (D/A) small molecules (M1, M2, and M3) based on aza-isatinylidene malononitrile (AIMN) and diketopyrrolopyrrole (DPP) containing different N-alkyl chains in AIMN unit were synthesized and characterized for application in solution-processable organic field-effect transistors (OFETs). The D/A small molecules with strongly electron-withdrawing AIMN and DPP units exhibited broad absorption spectra, low bandgaps, and deep lowest unoccupied molecular orbital energy levels (< – 4.0 eV). Consequently, OFET devices displayed unipolar electron transport characteristics with the highest electron mobilities of 0.26, 0.22, and 0.0079 cm2V–1s–1 for M1, M2, and M3, respectively. The small molecules with linear side chains showed much higher field-effect performances than that of branched side chains- based small molecule, due to the strong π–π stacking and appropriate morphology. This work indicated that the strongly electron-deficient AIMN should be a potential unit for constructing the n-type solution-processable small molecular semiconductors.