Highly planar cross-conjugated alternating polymers with multiple conformational locks: synthesis, characterization and their field-effect properties

It is meaningful to explore new design principles for organic semiconductors. Herein, we have developed two cross-conjugated alternating polymers based on 1,2-di(thiophen-2-yl)ethane-1,2-dione (DTO), namely PDTO-C1 and PDTO-C3, and investigated their charge transport properties by fabricating field-effect transistors devices. Single crystal X-ray crystallography shows that non-covalent S center dot center dot center dot O and C-H center dot center dot center dot 0 interactions exist inside the DTO units. These non-covalent interactions in combination with the C-H center dot center dot center dot 0 interactions of the thiophene-flanked dithienothiophene units, acting as conformational locks, are beneficial for acquiring the planar backbone conformation. PDTO-C1 and PDTO-C3 possess broad absorption spectra and HOMO and LUMO energy levels of ca. -5.50 and-3.6 eV, respectively. The highest mobility of 0.54 cm(2) V-1 s(-1) was achieved in the PDTO-C3-based transistor devices, whereas PDTO-C1 affords a mobility of 0.22 cm(2) V-1 s(-1). Further thin film microstructure investigations indicate that both polymers can form highly-ordered lamellar packing with small pi-pi stacking distances down to 3.50 angstrom. These results demonstrate that the incorporation of cross-conjugation may be used as an additional design tactic for organic semiconductors to alter their optoelectronic properties.