Thienoisoindigo (TII)-Based Quinoidal Small Molecules for High-Performance n-Type Organic Field Effect Transistors

A novel quinoidal thienoisoindigo (TII)-containing small molecule family with dicyanomethylene end-capping units and various alkyl chains is synthesized as n-type organic small molecules for solution-processable organic field effect transistors (OFETs). The molecular structure of the 2-hexyldecyl substituted derivative, TIIQ-b16, is determined via single-crystal X-ray diffraction and shows that the TIIQ core is planar and exhibits molecular layers stacked in a face-to-face arrangement with short core intermolecular distances of 3.28 angstrom. The very planar core structure, shortest intermolecular N center dot center dot center dot H distance (2.52 angstrom), existence of an intramolecular non-bonded contact between sulfur and oxygen atom (S center dot center dot center dot O) of 2.80 angstrom, and a very low-lying LUMO energy level of -4.16 eV suggest that TIIQ molecules should be electron transporting semiconductors. The physical, thermal, and electrochemical properties as well as OFET performance and thin film morphologies of these new TIIQs are systematically studied. Thus, air-processed TIIQ-b16 OFETs exhibit an electron mobility up to 2.54 cm(2) V-1 s(-1) with a current ON/OFF ratio of 10(5)-10(6), which is the first demonstration of TII-based small molecules exhibiting unipolar electron transport characteristics and enhanced ambient stability. These results indicate that construction of quinoidal molecule from TII moiety is a successful approach to enhance n-type charge transport characteristics.

Automated summary

A novel family of quinoidal thienoisoindigo (TII)-containing small molecules with dicyanomethylene end-capping units and different alkyl chains were synthesized for n-type organic small molecules in solution-processable organic field effect transistors (OFETs). The detailed molecular structure, properties, and performance of the 2-hexyldecyl substituted derivative, TIIQ-b16, were systematically studied, revealing its potential as electron transporting semiconductors with enhanced ambient stability. The results suggest that constructing quinoidal molecules from TII moiety is an effective approach to improve n-type charge transport characteristics.