Effect of Bending on the Electrical Characteristics of Flexible Organic Single Crystal-based Field-effect Transistors.

The charge transport in an organic semiconductor depends highly on the molecular packing in the crystal, which influences the electronic coupling immensely. However, in soft electronics, in which organic semiconductors play a critical role, the devices will be bent or folded repeatedly. The effect of bending on the crystal packing and thus the charge transport is crucial to the performance of the device. In this manuscript, we describe the protocol to bend a single crystal of 5,7,12,16-tetrachloro-6,13-diazapentacene (TCDAP) in the field-effect transistor configuration and to obtain reproducible I-V characteristics upon bending the crystal. The results show that bending a field-effect transistor prepared on a flexible substrate results in nearly reversible yet opposite trends in charge mobility, depending on the bending direction. The mobility increases when the device is bent toward the top gate/dielectric layer (upward, compressive state) and decreases when bent toward the crystal/substrate side (downward, tensile state). The effect of bending curvature was also observed, with greater mobility change resulting from higher bending curvature. It is suggested that the intermolecular π-π distance changes upon bending, thereby influencing the electronic coupling and the subsequent carrier transport ability.

Synthesis and Characterization of Polysubstituted Dibenzopyrenes as Charge-Transporting Materials.

A new class of benzopyrene-based semiconducting molecules is prepared and characterized. A four-step protocol involving Suzuki coupling and aromatic dehydrogenation reactions renders the new unsymmetrical framework. Introduction of various substituents at the dibenzopyrene framework modulates mainly the optoelectronic properties rather than the packing motif. Single-crystal field-effect transistors fabricated from these materials show a mobility ranging from 0.7 to 3.2 cm2/(V s). The highest mobility, 3.2 cm2/(V s), with an on/off ratio of 104-105 was achieved for 11-methoxy-8-(4-methoxyphenyl)dibenzo[a,e]pyrene.

Unsymmetrically Extended Polyfused Aromatics Embedding Coronene and Perylene Frameworks: Syntheses and Properties.

A series of polyfused aromatics containing coronene and perylene in their frameworks was successfully constructed by a modified Ramirez-Corey-Fuchs reaction as the key reaction. Typical six-membered annulation and atypical five-membered annulation through controlled reaction conditions led to a range of extensively conjugate aromatics as possible candidates for organic semiconductors. A significant p-type field-effect mobility of 0.42-0.64 cm(2)/V·s was obtained from one of the derivatives, dibenzo[a,d]coronene.