A series of syndiotatic P5CPn polymethylenes was prepared with 4-(trans-4-pentylcyclohexyl)phenoxy moieties linked to each backbone carbon atom via an alkyloxycarbonyl spacer and with even numbers of alkyl carbons n ranging from 2 to 14, and their thermotropic behaviors were investigated. The P5CPn, except P5CP2, formed smectic phases in which the rod-like polymethylene backbones were arranged in rectangular lattices, and the sidechain mesogens were aggregated into layers parallel to the shorter sides of the rectangular lattices. The packing of the mesogens changed with decreasing temperature from smectic C-like to smectic I-like (SmI-like) for n = 4−8 and from smectic Alike to SmI-like for n = 10−14. In the SmI-like phases, each mesogen along the main-chain axis was connected to every sixth backbone carbon atom, revealing a correlation between the packing of the mesogens and the main-chain conformation of a 3/2 helix. Conversely, P5CP2 formed a smectic phase with the main chains arranged in rows and with the mesogens barely aggregated into layers due to the short spacers.
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 1 H 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 cm 2 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.
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