Swallow-Tailed Alkyl and Linear Alkoxy-Substituted Dibenzocoronene Tetracarboxdiimide Derivatives: Synthesis, Photophysical Properties, and Thermotropic Behaviors

A series of dibenzocoronene tetracarboxdiimide derivatives decorated with alkyl swallow-tail and alkoxy moieties were synthesized, and their structures were characterized. 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as an effective oxidant was first used in the benzannulation of perylene diimides with the almost quantitative yield. The thermotropic behavior was investigated using differential scanning calorimetry (DSC) and polarization optical microscopy (POM). The introduction of alkyl swallow-tail and alkoxy substituents facilitates thermotropic liquid crystalline behavior. The branching site of alkyl swallow-tail units at the α position and the longer alkoxy chains played a similar role in lowering the mesophase transition as well as isotropization transition temperatures. The UV–vis absorption spectra of all compounds appeared as absorption in 425–600 nm region, and POM images of certain compounds exhibited characteristic columnar hexagonal (Col_h) packing and readily self-assembled into a homeotropic alignment toward the substrate

2D Organic Superlattice Promoted via Combined Action of π–π Stacking and Dipole–Dipole Interaction in Discotic Liquid Crystals

A series of discotic liquid crystals based on hexapentyloxytriphenylene (HAT5) have been investigated where one out of the six ether side chains of a triphenylene core was replaced by an ester side chain and named for <b><b>5a</b></b>–<b><b>5h</b></b>. During the process of studying these compounds, the characteristic straight line defect of ordered columnar structure was identified by polarizing optical microscopy (POM) and liquid crystal state over a wide temperature range was obtained by differential scanning calorimetry (DSC). Basic phase structure and molecular arrangement were assigned by one-dimensional wide-angle X-ray diffraction (1D WAXD), small-angle X-ray scattering (SAXS), two-dimensional wide-angle X-ray diffraction (2D WAXD), and transmission electron microscope (TEM). Combined with sharp and regular dots in 2D WAXD patterns and characteristic peaks at small angle in SAXS pattern which indicated the existence of superlattice, we proved that 2D superlattice formed from self-assembly of discotic molecules with a polar group via π–π stacking and dipole–dipole interaction. In order to verify the effect of orientation on charge carrier mobility, their electron and hole mobilities were measured by time-of-flight (TOF) device, among which the charge carrier mobility could achieve almost twice as that of HAT5. The formation of superlattice no doubt improved their electronic properties and made them more attractive in organic electronics