A π-Stacking Terthiophene-Based Quinodimethane Is an n-Channel Conductor in a Thin Film Transistor

Abstract

A terthiophene-based quinodimethane, 3',4'-dibutyl-5,5' '-bis(dicyanomethylene)-5,5' '-dihydro-2,2':5',2' '-terthiophene (1) was synthesized and crystallized. Compound 1 has a planar quinoid geometry that is stabilized by dicyanomethylene groups at each end of the molecule. In the crystal each molecule is part of a dimerized face-to-face pi-stack, with intermolecular spacings of 3.47 and 3.63 A, respectively. Cyclic voltammetry showed that 1 could be reversibly reduced and oxidized in methylene chloride solution. Thin film transistors (TFTs) were prepared by vacuum evaporation of 1 onto SiO2(300 nm)/Si substrates, followed by evaporation of Ag source and drain contacts. The doped Si substrate served as the gate electrode. X-ray diffraction and atomic force microscopy indicate the films are polycrystalline, with the long axes of the molecules approximately perpendicular to the substrate. The TFT measurements revealed n-channel conduction in films of 1, with room-temperature electron field effect mobilities as high as 0.005 cm2/Vs. The butyl side chains give 1 appreciable solubility in a range of common solvents, and preliminary TFT results on films cast from chlorobenzene show electron mobility as high as 0.002 cm2/Vs. These results indicate that pi-stacked quinoidal thiophene oligomers are a promising new class of soluble n-channel organic semiconductors.

Plastic electronic devices: From materials design to device applications

“…The improvement over earlier work was attributed to the particularly favorable polymer surface and was not related to the lengths of the oligomers [36]. Electron transport in FETs with mobility levels on the order of 0.1 cm 2 /Vs was demonstrated in two classes of oligothiophenes with electron withdrawing end groups [14,21,22,79].…”

High‐Performance n‐type Organic Semiconductors: Incorporating Specific Electron‐Withdrawing Motifs to Achieve Tight Molecular Stacking and Optimized Energy Levels

“…We demonstrated previously that -CN and -CF 3 units, if appropriately linked to the π-conjugated backbone, effectively promote highly crystalline condensed state structures, in particular, slip-stacked molecular arrangements with hierarchical organization and also reduce the LUMO levels [12] as was reported from other groups as well. [3][4][5][6][7] To explore the feasibility of using this class of materials as n-type semiconductors, 3'-(thiophene-2,5-diyl) bis(2-(3,5-bis(trifluoromethyl)phenyl)acrylonitrile (THIO-Y, see Figure 1a) bearing both CN-substituted stilbenic units and -CF 3 units was previously synthesized and investigated for its OFET characteristics. [12] THIO-Y exhibited a good n-type field-effect transistor performance with a maximum electron mobility of 0.16 cm 2 V −1 s −1 in single crystals.…”

“…[3] To increase the electron affinity (or decrease the lowest unoccupied molecular orbital (LUMO) level) of semiconductors, electron-withdrawing moieties, such as cyano (-CN), [4] fluorine (-F), [5] perfluoroalkyl (-CF 2 -), [6] and diimides [7] have been added to the π-conjugated building block molecules. Recently, our group has been actively involved in developing π-conjugated self-assembling molecules that form well-ordered organic nanostructures with controllable size and morphology for nano-optoelectronic device applications.…”

Stacking of oligo- and polythiophene cations in solution: Surface tension and dielectric saturation

“…Thiophene-derived oligomers and polymers represent today one of the most promising class of organic semiconductors, finding potential applications in a variety of electronic and electroactive devices. [16][17][18] Semiconducting properties arise with doping: therefore much of the basic research performed on these systems has addressed, in particular, the doped or oxidized species. Since the early 1990s electrochemical and spectroscopic evidences were gathered indicating that oxidized oligothiophenes reversibly associate in solution.…”