Atropisomeric conjugated diimides: a class of thermally responsive organic semiconductors

Atropisomerism has been studied in many research fields; however, it is rarely studied in organic semiconductors. In this work, we report a series of room-temperature-stable atropisomeric conjugated diimides, Syn-NDI and Anti-NDI based on 1,4,5,8-naphthalenetetracarboxylic diimides (NDIs) as well as Syn-PDI and Anti-PDI based on 3,4:9,10-perylenetetracarboxylic diimides (PDIs). For these two pairs of atropisomers, the Syn and Anti conformers can be interconverted when they are in heated solution, whereas in the solid state, only the Syn conformers can converted to Anti conformers when thermally annealed. This feature can be applied to realize thermally responsive organic field-effect transistors (OFETs). Remarkably, when thermally annealed at a certain temperature, the Syn atropisomers can be fast converted to their respective Anti ones, and OFETs originally based on the Syn semiconductors show a dramatic improvement in electron mobility. For OFETs originally based on Syn-NDI, a 100-fold improvement in electron mobility is recorded when Syn-NDI was converted to Anti-NDI, while for OFETs originally based on Syn-PDI, a 5000-fold improvement in electron mobility is recorded when Syn-PDI was converted to Anti-PDI. In contrast, thermal annealing is found to have a negligible effect for OFETs based on Anti semiconductors, with the electron mobility on the same order of magnitude for all Anti semiconductor devices. This is the first time that the atropisomerism has been exploited in organic semiconductors, demonstrating great potential for stimuli-responsive devices.