Halogen Substitution Effects on the Molecular Packing and Thin Film Transistor Performances of Carbazoledioxazine Derivatives

Solution-processable carbazoledioxazine derivatives with different halogen substituents (F, Cl, and Br) were newly synthesized by condensation and subsequent cyclization reactions. The chemical structures were confirmed by ¹H NMR and IR spectroscopies as well as MALDI-TOF mass spectrometry. All three carbazoledioxazines possessed a high thermal stability with decomposition temperatures exceeding 270 °C and exhibited thermal transitions upon heating. The phases were characterized by their wide-angle X-ray diffraction patterns at various temperatures. In addition, the energy levels of the carbazoledioxazines were estimated from the optical absorption spectra and electrochemical redox potentials of the thin films. All three derivatives displayed more or less the same energy levels: highest occupied molecular orbitals (HOMOs) of −5.3 eV and lowest unoccupied molecular orbitals (LUMOs) of −3.5 ∼ −3.6 eV. Despite this fact, the Br derivative showed higher hole mobilities with the maximum mobility of 4.9 × 10^–3 cm² V^–1 s^–1 in the thin film transistors as compared to those of the counter F and Cl derivatives. This was attributed to the bimodal carrier pathways formed through the monoclinic molecular orientation of the Br derivative, revealed by grazing-incidence X-ray diffraction (GIXRD) measurements.