Synthesis and characterization of poly(benzodithiophene) derivative for organic thin film transistors

Poly{2,6-bis(3-dodecylthiophen-2-yl) benzo[1,2-b;4,5-b']dithiophene} (PTBT) was synthesized, via oxidative polymerization by oxidative agent (FeCl₃). The mole ratio of FeCl₃ and monomer (3.5:1), and keeping low temperature during the dropping of diluted catalyst were very important for the polymerization without crosslinking. The PTBT was confirmed by ¹H NMR, FTIR spectra, and elemental analysis. The PTBT has very good solubility in organic solvents such as chloroform, tetrahydrofuran, etc, and good thermal stability with Tg of 164 °C. The PTBT shows UV-optical absorption at 406 nm and photoluminescence (PL) spectroscopy at 504 nm in a film. The highest occupied molecular orbital (HOMO) energy of the polymer is -5.71 eV by measuring cyclic voltammetry (CV). A solution-processed polymer thin film transistor device shows a mobility of 3 x 10⁻⁵ - 8 x 10⁻⁵ cm² V⁻¹ s⁻¹, and an on/off current ratio of 10⁴. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5277-5284, 2007