Effect of Molecular Packing on Field-Effect Performance of Single Crystals of Thienyl-Substituted Pyrenes

A series of pyrene derivatives containing thienyl groups, 1−3, has been prepared using the Suzuki coupling reaction. Recrystallization from solution and physical vapor transport (PVT) method afforded different types of crystals of 1. From the mixture of isomers of 2, the 1,8-isomer preferably crystallized from solution, whereas the 1,6-isomer crystal was obtained by the PVT method. Fabricating single-crystal-based field-effect transistors of the above compounds we directly compared the field-effect performance between the devices of the two isoforms of 1 and those of the two isomers of 2. Though the overlap integrals were calculated to be only ∼10−3, the best hole mobility reached 0.02 cm2 V−1 s−1 for one of the single crystals of 1. Intriguingly, for both 1 and 2 only one type of the crystal shows the field-effect characteristics, indicating the significance of molecular packing even in the absence of band transport among the poorly coupled molecules. The estimated intermolecular overlap integrals for each compound also imply that the minimum overlap integral of ∼10−2 eV is required for detection of the field-effect characteristics.