Swallow-Tailed Alkyl and Linear Alkoxy-Substituted
Dibenzocoronene Tetracarboxdiimide Derivatives: Synthesis, Photophysical
Properties, and Thermotropic Behaviors
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Abstract
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<sub>h</sub>) packing and readily self-assembled into
a homeotropic alignment toward the substrate