Cyanostyrylthiophene-Based Ambipolar Conjugated Polymers: Synthesis, Properties, and Analyses of Backbone Fluorination Effect

Herein,
we report the synthesis and characterization of a series
of ambipolar cyanostyryl­thiophene (CST)-based conjugated polymers
without or with fluorine substituents, namely PD-CST, PD-3F-CST, PD-23F-CST, and PD-25F-CST. With the change of the number or incorporating position of fluorine
substitutes on the novel CST unit, the electron mobilities
of field-effect transistors based on these polymers dramatically increased
from 0.0015 cm2 V–1 s–1 for PD-CST, 0.13 cm2 V–1 s–1 for PD-3F-CST, and 0.25 cm2 V–1 s–1 for PD-23F-CST to 0.53 cm2 V–1 s–1 for PD-25F-CST. AFM and GIXRD investigation
indicated that the annealed PD-25F-CST thin film possesses
stronger crystallization tendency and highly ordered lamellar packing
than those of the other polymers. Further theoretical calculations
and single-crystal X-ray diffraction analysis deeply revealed the
remarkable influences of the number and incorporating position of
fluorine substitutes on the frontier orbital energy levels, backbone
conformation, and charge transport properties of polymer semiconductors.