Side chain assisted different types of molecular aggregation and comparison of aggregation dependent field effect mobility

• Side chains provide different aggregation behaviors in organic semiconductors.
• Electrical property of organic semiconductors is affected by molecular aggregation.
• H-aggregation gives better horizontal charge mobility than J-aggregation.
• Intermolecular π-orbital overlap depends on the types of molecular aggregation.
• The domain size of crystalline phase is affected by the types of aggregation.

Solution-processable conjugated materials having same molecular configuration of both an electron donating N-phenylindole and an electron accepting diketopyrrolopyrrole derivative were directly synthesized through the regio-selective modification of 1-phenyl-1H-indole. The aggregation behavior of obtained DPIO and DPIE was characterized by means of UV–visible spectroscopy and 2-dimensional grazing-incidence X-ray diffraction. Both materials showed strong aggregation tendency in film, but DPIO and DPIE produced different types of molecular aggregation mostly due to the different side chains. In order to compare the aggregation-type dependent electrical property, DPIO and DPIE were adopted as semiconducting layers in organic field effect transistor, and DPIE produced much higher charge carrier mobility than DPIO. The better electrical properties of DPIE than DPIO was directly correlated with both larger intermolecular π-orbital overlap and well-connected crystalline phases.