n-Channel Organic Semiconductors Derived from Air-Stable Four-Coordinate Boron Complexes of Substituted Thienylthiazoles

Three acceptor-pi-bridge-acceptor (A-pi-A) molecules derived from 2-(3-boryl-2-thienyl)thiazole have been synthesized and thoroughly characterized. Incorporation of a B-N unit into thienylthiazole and attachment of suitable acceptor moieties allowed to obtain ambient-stable A-pi-A molecules with low-lying LUMO levels. Their potential for applications in organic electronics was tested in vacuum-deposited organic thin film transistors (OTFT). The OTFT device based on boryl-thienylthiazole and 1,1-dicyanomethylene-3-indanone (DCIND) acceptor moieties showed an electron mobility of approximate to 1.4 x 10(-2) cm(2)V(-1)s(-1) in air, which is the highest electron mobility reported to date for organoboron small molecules. Conversely, the device employing the malononitrile (MAL) derivative as an active layer did not show any charge transport behavior. As suggested by single crystal X-ray analysis of indandione (IND) and MAL derivatives, the enhanced mobility of IND (and DCIND) in comparison to the MAL molecule can be attributed to the effective two-dimensional pi-stacking in the solid state imparted by the acceptor moieties with an extended pi-surface.